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The alloys based on Ti-Zr are considered an excellent candidate for hydrogen storage applications. In this communication, we report the results of Fe substitution for Ni in the well-known Ti45Zr38Ni17 compound. The parent and related... more
The alloys based on Ti-Zr are considered an excellent candidate for hydrogen storage applications. In this communication, we report the results of Fe substitution for Ni in the well-known Ti45Zr38Ni17 compound. The parent and related compounds can be obtained as amorphous powders, transforming into the quasicrystalline phase (i-phase) after annealing. The amorphous Ti45Zr38Fe17 phase is transformed into the icosahedral quasicrystalline state, and it is a quasi-continuous process. The i-phase is well-developed close to 500 °C. At higher temperatures, the quasicrystal structure transforms into the other phase: the w-phase (an approximant to the crystalline phase) and another crystal phase with a small addition of the FeZr3 and the Fe2(ZrTi)3. The amorphous Ti45Zr38Fe17 phases can be hydrogenated while maintaining the amorphous nature, which constitutes another very fascinating research field for our group. The investigated alloy shows a good capacity for gaseous H2 at level 2.54 wt.% ...
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In this paper, we report on a successful synthesis of dysprosium iron garnet Dy3Fe5O12 (DyIG) by a reactive synthesis method involving dysprosium iron perovskite and hematite. Phase formation was traced using dilatometry, and XRD... more
In this paper, we report on a successful synthesis of dysprosium iron garnet Dy3Fe5O12 (DyIG) by a reactive synthesis method involving dysprosium iron perovskite and hematite. Phase formation was traced using dilatometry, and XRD measurements attested to the formation of the desired structure. Samples with relative density close to 97% were fabricated. The samples were characterized using vibrating sample magnetometry, dielectric spectroscopy, and UV-Vis-NIR spectroscopy. Magnetic properties were probed in temperatures between 80 and 700 K with a maximum applied field of 1 kOe. The measurements revealed several effects: the compensation of magnetic moments at a certain temperature, the inversion of the magnetocaloric effect, and the ability to measure the Curie temperature of the material. Activation energy was determined from UV-Vis-NIR and dielectric spectroscopy measurements. Characteristic magnetic temperatures and activation energy values of the samples were similar to bulk DyI...
Research Interests: Engineering, Materials Science, Sintering, Spectroscopy, Magnetic Materials, and 15 moreMagnetic refrigeration, Materials, Medicine, Magnetic field, Garnets, DIELECTRIC, Magnetic Properties, Activation Energy, CHEMICAL SCIENCES, Hematite, Curie temperature, Arrhenius Kinetic, Magnetism and Magnetic Materials, Solid State Reaction, and Dysprosium
Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal... more
Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal phases (i-phases), studies on their hydrogen storage properties have been extensively conducted for not only their industrial applications as hydrogen storage media, but also scientific interest in their local structures, using a proton as a probe. The Ti/ Zr-based i-phase has been mainly produced either by rapid-quenching or annealing the amorphous phase obtained by mechanical alloying (MA). We have systematically studied hydrogenation of the Ti/Zr-based amorphous and i-phase powders synthesized by MA and subsequent annealing respectively. In this chapter, we have reviewed the recent progress in the studies on hydrogenation of the Ti-Zr-Ni alloys and summarize our recent research results on both gaseous and electrochemical hydrogenation properties of the amorphous and the i-phase powders. The effects of the substitution or addition of some chemical elements on the microstructures and the hydrogenation properties have been investigated. Additionally, a comparison between the amorphous and the i-phases on the hydrogen properties as well as the results reported for the samples prepared by rapid-quenching will be made.
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Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES,... more
Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES, Mössbauer Spectroscopy, XPS, XAFS). Magnetic studies proved the paramagnetic response of stoichiometric ZnFe2O4 (ZF) nanoparticles, while superparamagnetic behavior was observed in as-synthesized, non-stoichiometric ZnxFe3−xO (NZF) nanoparticles. Upon annealing up to 1400 °C in an inert atmosphere, a significant change in the saturation magnetization of NZF nanoparticles was observed, which rose from approximately 50 up to 140 emu/g. We attribute this effect to the redistribution of cations in the spinel lattice and reduction of Fe3+ to Fe2+ during high-temperature treatment. Iron reduction is observed in both ZF and NZF nanoparticles, and it is related to the decomposition of zinc ferrite and associated sublimation of zinc oxide.
Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Synthesis of nanoparticles, Magnetic Materials, and 12 moreNanoparticle, Nanoparticles, Magnetic field, Magnetic Properties, Spinel, Superparamagnetism, Magnetism and Magnetic Materials, Stoichiometry, Magnetic Properties of Zinc Ferrite Nanoparticles, X Ray Photoelectron Spectroscopy, Zinc Ferrite, and Ferrite Nanoparticles
Research Interests: Condensed Matter Physics, Materials Science, Magnetic Materials, Dilute Magnetic Semiconductors, Nanowire, and 11 moreElectrodeposition, Medicine, Multidisciplinary, Doping, Crystallinity, Curie temperature, Magnetism and Magnetic Materials, Ferromagnetism, Antiferromagnetism, InSb Nanowire, and Paramagnetism
SUMMARY Magnetite is an abundant magnetic mineral that commonly records the ancient magnetic field in a wide variety of rock types. When cooled below ≈124 K, magnetite undergoes a phase transition, called the Verwey transition, whose... more
SUMMARY Magnetite is an abundant magnetic mineral that commonly records the ancient magnetic field in a wide variety of rock types. When cooled below ≈124 K, magnetite undergoes a phase transition, called the Verwey transition, whose characteristics are highly sensitive to grain size and stoichiometry. Studying the Verwey transition thus yields information on the formation conditions and compositions of rocks. The transition is also stress sensitive, thereby opening an avenue to understanding a rock’s strain history; however, the reason for the stress sensitivity is poorly understood. In particular, the temperature of the transition decreases when measured under pressure, yet mostly increases upon pressure release. Moreover, the stress sensitivity of the transition as a function of dopant concentration, especially after pressure cycling, was never systematically tested. We addressed these issues in order to further develop magnetite as a pressure gauge. Multidomain magnetite samples...
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When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its... more
When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5 nm, 10 nm, 15 nm), greater than the spin diffusion length. Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20 K to 300 K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface ...
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We present the spontaneous growth of self-assembled epitaxial nanostructures of BiFeO 3 (BFO) obtained by Pulsed Laser Deposition. The BFO phase architectures of squares, stripes and pyramids were grown on (0 0 1), (1 1 0) and (1 1 1)... more
We present the spontaneous growth of self-assembled epitaxial nanostructures of BiFeO 3 (BFO) obtained by Pulsed Laser Deposition. The BFO phase architectures of squares, stripes and pyramids were grown on (0 0 1), (1 1 0) and (1 1 1) SrTiO 3 (STO) substrates, respectively. The morphology of the BFO nanostructures was determined by Scanning Electron Microscopy and Atomic Force Microscopy revealing their vertical alignment and self-assembled feature on the surface of the entire substrate. Structural analysis was made along in-plane and outof-plane directions employing X-ray Diffraction. We determined the growth routes of BFO nanostructures and established a relationship between their morphology and structural properties. Such self-ordered crystalline nanostructures could be used as a tailored platform for the deposition of the ferromagnetic phase, thus providing an alternative method for the fabrication of BFO-based multiferroic vertically aligned nanocomposites.
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Changes in stoichiometry, temperature, strain and other parameters dramatically alter properties of LSMO perovskite. Thus, the sensitivity of LSMO may enable control of the magnetic properties of the film. This work demonstrates the... more
Changes in stoichiometry, temperature, strain and other parameters dramatically alter properties of LSMO perovskite. Thus, the sensitivity of LSMO may enable control of the magnetic properties of the film. This work demonstrates the capabilities of interface engineering to achieve the desired effects. Three methods of preparing STO substrates were conducted, i.e., using acid, buffer solution, and deionized water. The occurrence of terraces and their morphology depend on the preparation treatment. Terraces propagate on deposited layers and influence LSMO properties. The measurements show that anisotropy depends on the roughness of the substrate, the method of preparing the substrate, and oxygen treatment. The collected results suggest that the dipolar mechanism may be the source of LSMO anisotropy.
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We present the spontaneous growth of self-assembled epitaxial nanostructures of BiFeO 3 (BFO) obtained by Pulsed Laser Deposition. The BFO phase architectures of squares, stripes and pyramids were grown on (0 0 1), (1 1 0) and (1 1 1)... more
We present the spontaneous growth of self-assembled epitaxial nanostructures of BiFeO 3 (BFO) obtained by Pulsed Laser Deposition. The BFO phase architectures of squares, stripes and pyramids were grown on (0 0 1), (1 1 0) and (1 1 1) SrTiO 3 (STO) substrates, respectively. The morphology of the BFO nanostructures was determined by Scanning Electron Microscopy and Atomic Force Microscopy revealing their vertical alignment and self-assembled feature on the surface of the entire substrate. Structural analysis was made along in-plane and outof-plane directions employing X-ray Diffraction. We determined the growth routes of BFO nanostructures and established a relationship between their morphology and structural properties. Such self-ordered crystalline nanostructures could be used as a tailored platform for the deposition of the ferromagnetic phase, thus providing an alternative method for the fabrication of BFO-based multiferroic vertically aligned nanocomposites.
Research Interests:
In this paper, we report on a successful synthesis of dysprosium iron garnet Dy3Fe5O12 (DyIG) by a reactive synthesis method involving dysprosium iron perovskite and hematite. Phase formation was traced using dilatometry, and XRD... more
In this paper, we report on a successful synthesis of dysprosium iron garnet Dy3Fe5O12 (DyIG) by a reactive synthesis method involving dysprosium iron perovskite and hematite. Phase formation was traced using dilatometry, and XRD measurements attested to the formation of the desired structure. Samples with relative density close to 97% were fabricated. The samples were characterized using vibrating sample magnetometry, dielectric spectroscopy, and UV-Vis-NIR spectroscopy. Magnetic properties were probed in temperatures between 80 and 700 K with a maximum applied field of 1 kOe. The measurements revealed several effects: the compensation of magnetic moments at a certain temperature, the inversion of the magnetocaloric effect, and the ability to
measure the Curie temperature of the material. Activation energy was determined from UV-Vis-NIR and dielectric spectroscopy measurements. Characteristic magnetic temperatures and activation energy values of the samples were similar to bulk DyIG obtained using other methods.
measure the Curie temperature of the material. Activation energy was determined from UV-Vis-NIR and dielectric spectroscopy measurements. Characteristic magnetic temperatures and activation energy values of the samples were similar to bulk DyIG obtained using other methods.
Research Interests:
In this study, we report the synthesis of nanosized Al-substituted lithium-iron ferrites Li 0.5 Al x Fe 2.5-x O 4 (0 ≤ x ≤ 1) by sol-gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were... more
In this study, we report the synthesis of nanosized Al-substituted lithium-iron ferrites Li 0.5 Al x Fe 2.5-x O 4 (0 ≤ x ≤ 1) by sol-gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were studied using X-ray diffraction and impedance spectroscopy. The samples obtained by chemical methods have a higher homogeneity of the distribution of elements by volume, good repeatability of the result, high crystallinity, small crystallite size and perfect stoichiometry. Based on Koop's theory, the basic regularities of the behavior of the dielectric constant and the loss tangent are explained. The jump mechanism of conductivity has been realized by the transition of an electron between iron ions in different valence states. Samples synthesized by the sol-gel auto-combustion show technological characteristics, compared with systems obtained by solid-phase method.
Research Interests:
The alloys based on Ti-Zr are considered an excellent candidate for hydrogen storage applications. In this communication, we report the results of Fe substitution for Ni in the well-known Ti45Zr38Ni17 compound. The parent and related... more
The alloys based on Ti-Zr are considered an excellent candidate for hydrogen storage applications. In this communication, we report the results of Fe substitution for Ni in the well-known Ti45Zr38Ni17 compound. The parent and related compounds can be obtained as amorphous powders, transforming into the quasicrystalline phase (i-phase) after annealing. The amorphous Ti45Zr38Fe17 phase is transformed into the icosahedral quasicrystalline state, and it is a quasi-continuous process. The i-phase is well-developed close to 500 ◦C. At higher temperatures, the quasicrystal structure transforms into the other phase: the w-phase (an approximant to the crystalline phase) and another
crystal phase with a small addition of the FeZr3 and the Fe2(ZrTi)3
. The amorphous Ti45Zr38Fe17 phases can be hydrogenated while maintaining the amorphous nature, which constitutes another very fascinating research field for our group. The investigated alloy shows a good capacity for gaseous H2 at level 2.54 wt.% at elevated temperatures. The ferromagnetic signal of the amorphous TiZrFe comes from magnetic nanocrystallites in the amorphous matrix. After heating, the magnetic
signal significantly decreases due to the lack of long-range magnetic ordering in the i-phase of the Ti45Zr38Fe17 alloy.
crystal phase with a small addition of the FeZr3 and the Fe2(ZrTi)3
. The amorphous Ti45Zr38Fe17 phases can be hydrogenated while maintaining the amorphous nature, which constitutes another very fascinating research field for our group. The investigated alloy shows a good capacity for gaseous H2 at level 2.54 wt.% at elevated temperatures. The ferromagnetic signal of the amorphous TiZrFe comes from magnetic nanocrystallites in the amorphous matrix. After heating, the magnetic
signal significantly decreases due to the lack of long-range magnetic ordering in the i-phase of the Ti45Zr38Fe17 alloy.
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This article shows how initial composition and thermal treatment of nonstoichiometric zinc ferrite nanoparticles (nZFN) can be chosen to adjust the structure and cation distribution and enhance magnetism in the resulting nanoscale... more
This article shows how initial composition and thermal treatment of nonstoichiometric zinc ferrite nanoparticles (nZFN) can be chosen to adjust the structure and cation distribution and enhance magnetism in the resulting nanoscale material. It also provides insight into new prospects regarding the production and design of nanoscale materials. Investigations were conducted before and after heating of nZFN in an inert atmosphere and a vacuum up to temperature of 1170°C. Annealing leads to partial reduction of Fe ions, enhanced magnetism, and an increase in the size of the particles independent of the atmosphere. Use of the inert atmosphere delivers a solid solution of magnetite and zinc ferrite with a reduced Zn content in the structure as a result of sublimation of newly formed ZnO and reduction of Fe, and it favors crystallization. A preference for normal-spinel phase and enhancement of magnetic saturation from 20 Am 2 /kg up to 101 Am 2 /kg was observed. Vacuum annealing with high probability produces ZnO, Fe 3 O 4 , and Fe 2 O 3 multiphase system with signs of amorphization, mainly on the surface. A large fraction of Fe ions is reduced and the volume ratio of Fe 3 O 4 to Fe 2 O 3 increases with heating time. The final solid product from a complete decomposition of ZFN is magnetite.
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This article describes the static, dynamic, and temperature dependent magneto-transport properties of the Fe/BTO/LSMO mutliferroic tunnel junction (MFTJ). The multilayer structure is grown on a high quality crystalline STO substrate by... more
This article describes the static, dynamic, and temperature dependent
magneto-transport properties of the Fe/BTO/LSMO mutliferroic tunnel junction (MFTJ). The multilayer structure is grown on a high quality crystalline STO substrate by means of pulsed laser deposition, which enables epitaxial layer-by-layer growth. The MFTJ is patterned into micrometer-size devices by means of the ion-etching-free lithography process ensuring that the properties of the oxide layers are preserved after the device fabrication. The measured static properties indicate that the MFTJ has multiferroic properties at room temperature with the tunneling electroresistance (TER) and tunneling magnetoresistance (TMR) reaching 270% and 0.4%, respectively. The temperature measurements indicate the exponentially decreasing dependence of TMR with increasing temperature, whereas TER is temperature independent. The electric ferromagnetic resonance measurements based on the spin-diode
effect shows the existence of two resonance peaks, from both ferromagentic electrodes, one identified as LSMO-derived and characterized by low magnetization damping of α = 0.002 and the other from the Fe.
magneto-transport properties of the Fe/BTO/LSMO mutliferroic tunnel junction (MFTJ). The multilayer structure is grown on a high quality crystalline STO substrate by means of pulsed laser deposition, which enables epitaxial layer-by-layer growth. The MFTJ is patterned into micrometer-size devices by means of the ion-etching-free lithography process ensuring that the properties of the oxide layers are preserved after the device fabrication. The measured static properties indicate that the MFTJ has multiferroic properties at room temperature with the tunneling electroresistance (TER) and tunneling magnetoresistance (TMR) reaching 270% and 0.4%, respectively. The temperature measurements indicate the exponentially decreasing dependence of TMR with increasing temperature, whereas TER is temperature independent. The electric ferromagnetic resonance measurements based on the spin-diode
effect shows the existence of two resonance peaks, from both ferromagentic electrodes, one identified as LSMO-derived and characterized by low magnetization damping of α = 0.002 and the other from the Fe.
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Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES,... more
Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES, Mo¨ssbauer Spectroscopy, XPS, XAFS). Magnetic studies proved the paramagnetic response of stoichiometric ZnFe 2 O 4 (ZF) nanoparticles, while superparamagnetic behavior was observed in as-synthesized, non-stoichiometric Zn x Fe 3Àx O (NZF) nanoparticles. Upon annealing up to 1400°C in an inert atmosphere, a significant change in the saturation magnetization of NZF nanoparticles was observed, which rose from approximately 50 up to 140 emu/g. We attribute this effect to the redistribution of cations in the spinel lattice and reduction of Fe 3+ to Fe 2+ during high-temperature treatment. Iron reduction is observed in both ZF and NZF nanoparticles, and it is related to the decomposition of zinc ferrite and associated sublimation of zinc oxide.
Research Interests:
In this study, we report the synthesis of nanosized Al-substituted lithium-iron ferrites Li 0.5 Al x Fe 2.5-x O 4 (0 ≤ x ≤ 1) by sol-gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were... more
In this study, we report the synthesis of nanosized Al-substituted lithium-iron ferrites Li 0.5 Al x Fe 2.5-x O 4 (0 ≤ x ≤ 1) by sol-gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were studied using X-ray diffraction and impedance spectroscopy. The samples obtained by chemical methods have a higher homogeneity of the distribution of elements by volume, good repeatability of the result, high crystallinity, small crystallite size and perfect stoichiometry. Based on Koop's theory, the basic regularities of the behavior of the dielectric constant and the loss tangent are explained. The jump mechanism of conductivity has been realized by the transition of an electron between iron ions in different valence states. Samples synthesized by the sol-gel auto-combustion show technological characteristics, compared with systems obtained by solid-phase method.
Research Interests:
Changes in stoichiometry, temperature, strain and other parameters dramatically alter properties of LSMO perovskite. Thus, the sensitivity of LSMO may enable control of the magnetic properties of the film. This work demonstrates the... more
Changes in stoichiometry, temperature, strain and other parameters dramatically alter properties of LSMO perovskite. Thus, the sensitivity of LSMO may enable control of the magnetic properties of the film. This work demonstrates the capabilities of interface engineering to achieve the desired effects. Three methods of preparing STO substrates were conducted, i.e., using acid, buffer solution, and deionized water. The occurrence of terraces and their morphology depend on the preparation treatment. Terraces propagate on deposited layers and influence LSMO properties. The measurements show that anisotropy depends on the roughness of the substrate, the method of preparing the substrate, and oxygen treatment. The collected results suggest that the dipolar mechanism may be the source of LSMO anisotropy.
Research Interests:
In this study, we report the influence of Co 2+ on structure and magnetic properties of nano-sized Li 0.5−x/2 Fe 2.5−x/2 Co x O 4 (where x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) synthesized using sol-gel auto-combustion method. The X-ray... more
In this study, we report the influence of Co 2+ on structure and magnetic properties of nano-sized Li 0.5−x/2 Fe 2.5−x/2 Co x O 4 (where x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) synthesized using sol-gel auto-combustion method. The X-ray diffractometric analysis of samples confirmed the formation of pure Li 0.5−x 2Fe 2.5−x 2Co x O 4 nanoparticles ranges crystallite size from 36 to 43 nm with co-doping. There is a structural transformation from ordered P4 3 32 to random Fd3m observed, which is caused by the localization of cobalt ions. RT-Mössbauer the showed presence of 57Fe in both sublattices. Position identification was performed based on the distribution of the over exchange fields and isomeric shift data. Magnetic measurements showed that the saturation magnetization increases to x ≤ 0.8 and then decreases with Co-content due to the change in cationic distribution. The cobalt substitution turns Li-Co ferrite from soft-magnet to hard-magnet.
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Single-phase multicomponent perovskite-type cobalt oxide containing five cations in equiatomic amounts on the Asite, namely, (Gd 0.2 Nd 0.2 La 0.2 Sm 0.2 Y 0.2)CoO 3 , has been synthesized via the modified coprecipitation hydrothermal... more
Single-phase multicomponent perovskite-type cobalt oxide containing five cations in equiatomic amounts on the Asite, namely, (Gd 0.2 Nd 0.2 La 0.2 Sm 0.2 Y 0.2)CoO 3 , has been synthesized via the modified coprecipitation hydrothermal method. Using an original approach for heat treatment, which comprises quenching utilizing liquid nitrogen as a cooling medium, a single-phase ceramic with high configuration entropy, crystallizing in an orthorhombic distorted structure was obtained. It reveals the anomalous temperature dependence of the lattice expansion with two weak transitions at approx. 80 and 240 K that are assigned to gradual crossover from the low-via intermediate-to high-spin state of Co 3+. The compound exhibits weak ferromagnetism at T ≤ 10 K and signatures of antiferromagnetic correlations in the paramagnetic phase. Ab initio calculations predict a band gap Δ = 1.18 eV in the ground-state electronic structure with the dominant contribution of O_p and Co_d orbitals in the valence and conduction bands, respectively. Electronic transport measurements confirm the negative temperature coefficient of resistivity characteristic to a semiconducting material and reveal a sudden drop in activation energy at T ∼ 240 K from E a ∼ 1 eV in the low-temperature phase to E a ∼ 0.3 eV at room temperature. The possibility of fine tuning of the semiconducting band gap via a subtle change in A-site stoichiometry is discussed.
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This paper presents electron magnetic resonance (EMR) and vibrating sample magnetometry (VSM) study of Heusler alloy Ni Mn In 50 35.5 14.5 ribbons prepared by melt spinning. The temperature dependency of the EMR spectra and magnetization... more
This paper presents electron magnetic resonance (EMR) and vibrating sample magnetometry (VSM) study of Heusler alloy Ni Mn In 50 35.5 14.5 ribbons prepared by melt spinning. The temperature dependency of the EMR spectra and magnetization was measured during the cooling and heating process in the 180-330 K and 100-450 K temperature ranges, respectively. Both methods reveal thermal hysteresis (structural phase transition) and metamagnetic character of this material. The morphology and composition were investigated by scanning electron microscopy (SEM) with an energy-dispersive spectrometer (EDS).
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The successful synthesis of one-dimensional nanostructures of a narrow band gap semiconductor, exhibiting a ferromagnetic response at room temperature, is reported. High-quality nanowires of InSb-Mn have been produced by templateassisted... more
The successful synthesis of one-dimensional nanostructures of a narrow band gap semiconductor, exhibiting a ferromagnetic response at room temperature, is reported. High-quality nanowires of InSb-Mn have been produced by templateassisted pulse electrodeposition. Detailed structural and spectroscopic characterizations revealed good crystallinity, a narrow size distribution of the nanostructures, and the ability to control the Mn doping level. The dominating magnetic response at a cryogenic temperature evolves with an increasing Mn concentration from paramagnetic through antiferromagnetic to ferromagnetic. A robust ferromagnetic response of InSb nanowires doped with 2.5% at. of Mn is retained up to a Curie temperature of nearly 500 K.
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Magnetite is an abundant magnetic mineral that commonly records the ancient magnetic field in a wide variety of rock types. When cooled below ≈124 K, magnetite undergoes a phase transition, called the Verwey transition, whose... more
Magnetite is an abundant magnetic mineral that commonly records the ancient magnetic field in a wide variety of rock types. When cooled below ≈124 K, magnetite undergoes a phase transition, called the Verwey transition, whose characteristics are highly sensitive to grain size and stoichiometry. Studying the Verwey transition thus yields information on the formation conditions and compositions of rocks. The transition is also stress sensitive, thereby opening an avenue to understanding a rock's strain history; however, the reason for the stress sensitivity is poorly understood. In particular, the temperature of the transition decreases when measured under pressure, yet mostly increases upon pressure release. Moreover, the stress sensitivity of the transition as a function of dopant concentration, especially after pressure cycling, was never systematically tested. We addressed these issues in order to further develop magnetite as a pressure gauge. Multidomain magnetite samples were pressure cycled up to maximum pressures of ∼5 GPa at room temperature to measure the influence of strain on the Verwey transition temperature as a function of dopant concentration after full decompression. The transition temperature measured via changes in magnetic remanence (T M V) systematically increased with respect to pressure (P) in more doped samples, where domain wall pinning from impurities dominates dT M V /dP. In less doped samples, no to only moderate pressure cycling dependence on T M V was observed. Bulk coercive force (B c) and magnetic remanence after saturation (M rs) measured above or below the transition also increased with respect to pressure, but here effects related to permanent strain of the lattice structure prevail, and B c versus P is steeper for less doped samples. B c versus P increases in all cases, with a difference in slope dictated by dopant concentrations segregating the first to second-order nature of the transition. Thus, strain developed during pressure cycling controls T M V and coercivity by a mechanism based on pinning of magnetic domains by both interstitial cations and structural lattice distortions. The combined observables, T M V and B c −M rs , reflect both the dopant level and strain state of magnetite, which can quantify the pressure multidomain magnetite has experienced, especially in the range between 1 and 5 GPa. Based on these new results, we present a model that distinguishes between electronic versus defect-driven processes explaining the strain-related influences on the transition. Magnetite's use as a geobarometer is thus a measure of its defect state, which is expressed through two somewhat independent mechanisms when sensed by magnetic observations.
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Magnetic properties and exchange bias of Ni 45 Co 5 Mn 35.5 In 14.5 ribbons were investigated by vibrating sample magnetometry (VSM) and electron magnetic resonance (EMR). Curie temperatures determined by using VSM and EMR methods are... more
Magnetic properties and exchange bias of Ni 45 Co 5 Mn 35.5 In 14.5 ribbons were investigated by vibrating sample magnetometry (VSM) and electron magnetic resonance (EMR). Curie temperatures determined by using VSM and EMR methods are equal to 374 K and 377 K, respectively. Additionally, the EMR measurements revealed the existence of a weak ferromagnetic resonance (FMR) line in the paramagnetic region. The upward deviation of the integral intensity from Curie-Weis low below temperature T * and above T C confirms the existence of ferromagnetic phase in this temperature region. Below T C , the integral intensity does not saturate, which can suggest the coexistence of different magnetic phases at low temperature range. Additional confirmation on the coexistence of magnetic phases in the sample are asymmetric hysteresis loops associated with the spontaneous exchange bias effect. The dependence of EMR signal on cyclic repetition of measurement is also discussed.
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The effect of Cu substitution for Ni on the structural and magnetocaloric properties in Ni 44Àx Cu x Co 6 Mn 39 Sn 11 (x ¼ 0-4 at.%) bulk Heusler alloys is studied. It is reported that Cu addition stabilizes austenite phase. Generally,... more
The effect of Cu substitution for Ni on the structural and magnetocaloric properties in Ni 44Àx Cu x Co 6 Mn 39 Sn 11 (x ¼ 0-4 at.%) bulk Heusler alloys is studied. It is reported that Cu addition stabilizes austenite phase. Generally, martensitic transformation temperature decreases with an increase of Cu concentration up to 4 at.%. The addition of 1 and 2 at.% of Cu allows to shift the temperature of martensitic transformation close to room temperature, while the strong inverse magnetocaloric effect is observed in alloys containing 0-3 at.% of Cu. The value of magnetic entropy at low magnetic field of 15 kOe evolves from 6.3 J kg À1 K À1 for Cu0 to 9.7 J kg À1 K À1 for Cu1, 7.1 J kg À1 K À1 for Cu2, 8.6 J kg À1 K À1 for Cu3, and 4.1 J kg À1 K À1 for Cu4 alloys. The estimated value of the effective refrigerant capacity, including hysteresis loss, is equal to 74.
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When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its... more
When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5nm, 10nm, 15nm), greater than the spin diffusion length. Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20K to 300K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost temperature-independent spin Hall angle of θ ≈ −0 2. SHN in Ta and a strongly temperature-dependent θSHN for the intermixed Ta/CoFeB interface.
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When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its... more
When a current is passed through a non-magnetic metal with strong spin-orbit coupling, an orthogonal spin current is generated. This spin current can be used to switch the magnetization of an adjacent ferromagnetic layer or drive its magnetization into continuous precession. The interface, which is not necessarily sharp, and the crystallographic structure of the nonmagnetic metal can both affect the strength of current-induced spin-orbit torques. Here, we investigate the effects of interface intermixing
and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5nm, 10nm, 15nm), greater than the spin diffusion length.
Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20K to 300K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost
temperature-independent spin Hall angle of θ ≈ −0 2. SHN in Ta and a strongly temperature-dependent θSHN for the intermixed Ta/CoFeB interface.
and film microstructure on spin-orbit torques in perpendicularly magnetized Ta/Co40Fe40B20/MgO trilayers with different Ta layer thickness (5nm, 10nm, 15nm), greater than the spin diffusion length.
Effective spin-orbit torques are determined from harmonic Hall voltage measurements performed at temperatures ranging from 20K to 300K. We account for the temperature dependence of damping-like and field-like torques by including an additional contribution from the Ta/CoFeB interface in the spin diffusion model. Using this approach, the temperature variations of the spin Hall angle in the Ta underlayer and at the Ta/CoFeB interface are determined separately. Our results indicate an almost
temperature-independent spin Hall angle of θ ≈ −0 2. SHN in Ta and a strongly temperature-dependent θSHN for the intermixed Ta/CoFeB interface.
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Heusler alloy Ni 48 Mn 39.5 Sn 12.5Àx Al x (x ¼ 0, 1, 2,3) ribbons were prepared by melt spinning. The cross section of ribbons reveals a typical heterogeneous microstructure consisting of small equi-axed and columnar grains. The top and... more
Heusler alloy Ni 48 Mn 39.5 Sn 12.5Àx Al x (x ¼ 0, 1, 2,3) ribbons were prepared by melt spinning. The cross section of ribbons reveals a typical heterogeneous microstructure consisting of small equi-axed and columnar grains. The top and bottom ribbons sides are homogenous in composition but they differ in terms of surface structure. The wheel ribbon side appears smoother and shows some degree of macroscopic organization. On the other hand the free ribbon surface regardless of composition shows a more complex morphology consisting of small equi-axed grains, larger grains forming clusters and conical sub crystal structures. A characteristic twinned plate like microstructure confirming the presence of an increased amount of martensite has been observed for the Ni 48 Mn 39.5 Sn 9.5 Al 3 ribbon. The martensitic plates are 70e100 nm in size. The phase shift of 0.5 was detected, while scanning the latter ribbon sample in magnetic force microscope mode, indicating the existence of a magnetic multi-domain structure in this sample.
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The effect of substitution of Co for Ni on hydrogen storage characteristics of Ti-Zr-Ni/Co powders (Ti 45-Zr 38 Ni 17Àx Co x (x = 4, 8)) produced by mechanical alloying (MA) was investigated. The final product after MA was amorphous for... more
The effect of substitution of Co for Ni on hydrogen storage characteristics of Ti-Zr-Ni/Co powders (Ti 45-Zr 38 Ni 17Àx Co x (x = 4, 8)) produced by mechanical alloying (MA) was investigated. The final product after MA was amorphous for all the powders, but subsequent annealing caused the formation of the icosahedral quasicrystal (i) phase with a Ti 2 Ni type crystal and a C14 like Laves phases. The amount of i-phase decreased, and reversely those of Ti 2 Ni and the Laves phases increased with increasing the amount of Co. After hydrogenation at 573 K and at an initial hydrogen pressure of 3.8 MPa, the maximum hydrogen concentration for the annealed powders reached was about 58 at%, and all the phases in the powders transformed to metallic hydrides ((Zr,Ti)H 2 , Ni(Zr,Ti)H 3 and Co(Zr,Ti)H 3). Because of the formation of several hydrides, accelerated hydrogen desorption occurred at several temperatures. The activation energies for hydrogen desorption varied from about 70 kJ/mol to 180 kJ/mol.
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BACKGROUND Size and shape of material can greatly influence its electronic structure and thus material’s functional properties relevant for applications. Lowering the dimension of magnetic materials and introducing structural damage to... more
BACKGROUND Size and shape of material can greatly influence its electronic structure and thus material’s functional properties relevant for applications. Lowering the dimension of magnetic materials and introducing structural damage to outer layers during nanostructurization not only enhances the impact of surface states but it may also change the volume properties, e.g. magnetic anisotropy. Understanding those processes and how they influence the properties known from bulk samples, cannot be achieved without the knowledge on structural defects, especially of those related to nanostructurization.
In this study, we report the synthesis of nanosized Al-substituted lithium–iron ferrites Li 0.5 Al x Fe 2.5- x O 4 (0 ≤ x ≤ 1) by sol–gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were... more
In this study, we report the synthesis of nanosized Al-substituted lithium–iron ferrites Li 0.5 Al x Fe 2.5- x O 4 (0 ≤ x ≤ 1) by sol–gel auto-combustion method and by ceramic method with double sintering. Synthesized materials were studied using X-ray diffraction and impedance spectroscopy. The samples obtained by chemical methods have a higher homogeneity of the distribution of elements by volume, good repeatability of the result, high crystallinity, small crystallite size and perfect stoichiometry. Based on Koop's theory, the basic regularities of the behavior of the dielectric constant and the loss tangent are explained. The jump mechanism of conductivity has been realized by the transition of an electron between iron ions in different valence states. Samples synthesized by the sol–gel auto-combustion show technological characteristics, compared with systems obtained by solid-phase method.
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Abstract An influence of the Cu doping on structural, magnetic and thermoelastic properties of the Heusler Ni44-xCuxCo6Mn39Sn11 (x = 1–4 at%) ribbons has been investigated. It is found that the addition of Cu stabilizes austenite phase.... more
Abstract An influence of the Cu doping on structural, magnetic and thermoelastic properties of the Heusler Ni44-xCuxCo6Mn39Sn11 (x = 1–4 at%) ribbons has been investigated. It is found that the addition of Cu stabilizes austenite phase. Martensite transformation (MT) temperatures generally decrease when Cu concentration increases, which is attributed to the atom size effect. The inverse magnetocaloric and elastocaloric effects in the vicinity of MT under moderate magnetic fields and stresses have been evaluated. Small Cu addition enhances both effects as compared to quaternary Ni–Co–Mn–Sn alloy. The magnetic entropy change under low magnetic field of 15 kOe increases from 2.9 J kg−1K−1 for Cu0 to 6.3 J kg−1K−1 for Cu2.
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Abstract Korea has developed an advanced reduced-activation alloy (ARAA) as a structural material for helium-cooled ceramic reflector test blanket module (HCCR-TBM) applications. The present paper describes the history of alloy... more
Abstract Korea has developed an advanced reduced-activation alloy (ARAA) as a structural material for helium-cooled ceramic reflector test blanket module (HCCR-TBM) applications. The present paper describes the history of alloy development and the properties of ARAA, which has been produced at a 5 t scale using vacuum induction melting and electro-slag re-melting methods. ARAA is a 9Cr–1.2W based ferritic–martensitic steel with 0.01 wt.% Zr. The mechanical properties, thermal properties and physical and magnetic properties of ARAA show similar temperature dependencies to those observed for Eurofer 97. However, ARAA exhibits a much longer creep–rupture time than conventional RAFM steel, which suggests a positive effect on Zr addition. The enhanced creep strength of ARAA by the addition of Zr is attributed to the reduced temperature-dependence of the yield strength.
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Abstract The effect of ball milling and subsequently annealing of melt spun ribbons on magneto-structural transformations in Ni50Mn37.5Sn12.5−xInx (x=0, 2, 4, 6) ribbons is presented. Short time vibration milling allows to obtain... more
Abstract The effect of ball milling and subsequently annealing of melt spun ribbons on magneto-structural transformations in Ni50Mn37.5Sn12.5−xInx (x=0, 2, 4, 6) ribbons is presented. Short time vibration milling allows to obtain chemically homogenous powders of angular particle shapes and size within 10–50 μm. Milling does not change the characteristic temperatures of martensitic transformation in comparison to the melt spun ribbons. The effect of In substitution for Sn on martensitic transformation has a complex mechanism, associated with electron density change. Substitution of Sn by In in both milled and annealed powders leads to decrease of Curie temperature of austenite and increase of martensitic transformation temperature, stabilizing martensitic phase. The coexistence of magnetic transformation of austenite and martensitic transformation at low magnetic field was observed. The intermartensitic transformation of 4O martensite to L10 martensite was observed during cooling at low magnetic field and this was confirmed by TEM microstructure observations. The annealing process of as-milled powders leads to the change of their martensitic structure due to relaxation of internal stresses associated with anisotropic columnar grain microstructure formed during melt spinning process. The level of stresses introduced during milling of ribbons has no significant influence on martensitic transformation. The annealing process of as milled powders leads to enhancement of their magnetic properties, decrease of Curie temperature of austenite, and marginal change of temperature of martenisitic transformation.
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Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal... more
Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal phases (i-phases), studies on their hydrogen storage properties have been extensively conducted for not only their industrial applications as hydrogen storage media, but also scientific interest in their local structures, using a proton as a probe. The Ti/ Zr-based i-phase has been mainly produced either by rapid-quenching or annealing the amorphous phase obtained by mechanical alloying (MA). We have systematically studied hydrogenation of the Ti/Zr-based amorphous and i-phase powders synthesized by MA and subsequent annealing respectively. In this chapter, we have reviewed the recent progress in the studies on hydrogenation of the Ti-Zr-Ni alloys and summarize our recent research results on both gaseous and electrochemical hydrogenation properties of the amorphous and the i-phase powders. The effects of the substitution or addition of some chemical elements on the microstructures and the hydrogenation properties have been investigated. Additionally, a comparison between the amorphous and the i-phases on the hydrogen properties as well as the results reported for the samples prepared by rapid-quenching will be made.
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Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal... more
Icosahedral (i) quasicrystals, which have a new type of translational long-range order and display a non-crystallographic rotational symmetry, were first observed in the Al-Mn alloy. Since the discovery of the Ti-Zr-Ni i quasicrystal phases (i-phases), studies on their hydrogen storage properties have been extensively conducted for not only their industrial applications as hydrogen storage media, but also scientific interest in their local structures, using a proton as a probe. The Ti/ Zr-based i-phase has been mainly produced either by rapid-quenching or annealing the amorphous phase obtained by mechanical alloying (MA). We have systematically studied hydrogenation of the Ti/Zr-based amorphous and i-phase powders synthesized by MA and subsequent annealing respectively. In this chapter, we have reviewed the recent progress in the studies on hydrogenation of the Ti-Zr-Ni alloys and summarize our recent research results on both gaseous and electrochemical hydrogenation properties of the amorphous and the i-phase powders. The effects of the substitution or addition of some chemical elements on the microstructures and the hydrogenation properties have been investigated. Additionally, a comparison between the amorphous and the i-phases on the hydrogen properties as well as the results reported for the samples prepared by rapid-quenching will be made.