In this study thin film samples of Ga1‐xMnxN were grown by pulsed laser deposition on Al2O3 (0001... more In this study thin film samples of Ga1‐xMnxN were grown by pulsed laser deposition on Al2O3 (0001) substrates. X‐ray diffraction measurements have confirmed these thin films exhibit hexagonal wurtzite structure. SQUID measurements show room temperature ferromagnetism of these dilute magnetic semiconductors (DMS). The techniques of X‐ray absorption and soft X‐ray emission spectroscopy at the N K‐edge were used to study the changes in the unoccupied and occupied N 2p partial density of states respectively as a function of dopant concentration. These element and site specific spectroscopies allow us to characterise the electronic structure of these doped materials and reveal the influence of the Mn doping on the valence band as measured through the N 2p partial density of states. X‐ray absorption measurements at the Mn L‐edge confirm significant substitutional doping of Mn into Ga‐sites. Finally, measurements of heavily Mn‐doped films using both soft X‐ray absorption and resonant soft ...
Amorphous melt-spun Pr2(Fe1−xCox)14B has been prepared to test the concept of magnetic-field-indu... more Amorphous melt-spun Pr2(Fe1−xCox)14B has been prepared to test the concept of magnetic-field-induced crystallite alignment. Crystallization temperatures (Tx) of alloys with x=0.5, 0.6, and 1.0 were determined to be 622, 646, and 507 °C, respectively. These temperatures are all lower than the Curie temperatures (Tc) of the crystallized 2:14:1 phase. The glasses were then heat treated at a temperature Tt(Tx<Tt<Tc), either in no field or in a magnetic field of 0.3 T applied parallel to the long edge of the ribbon. The degree of alignment was investigated by means of x-ray diffraction and magnetization measurements. A texture was found where the c axes tend to lie in the ribbon plane in zero field, which is slightly modified when a magnetic field is applied during the heat treatment.
A method for the controlled fabrication of a nickel perpendicular nanocontact with diameters less... more A method for the controlled fabrication of a nickel perpendicular nanocontact with diameters less than 5 nm is reported. The method involves milling pores through the 100 nm thick silicon nitride membrane using a focused ion beam, and depositing thin Ni film on the both side of the silicon nitride membrane. The shape of the resulting pore and nanocontact size is determined by the initial hole size and redeposition of the sputtered material onto the sidewalls of the holes. A sub-5 nm Ni nanocontact was prepared and the I-V and R-H characteristics measured.
Solutions to the main problems in operating a spin-polarized scanning tunneling microscope are di... more Solutions to the main problems in operating a spin-polarized scanning tunneling microscope are discussed. Preliminary experimental results obtained in the course of implementing these solutions are reported. Atomic resolution on Si(111) and Si(100) is achieved with a scanning tunneling microscope (STM) using chromium and iron tips. Fabrication of antiferromagnetic tips of Cr, MnNi, and MnPt is described. A technique of preparation of clean (100) surfaces of Fe3O4 (magnetite) is given. Low-energy electron diffraction patterns were obtained on Fe3O4 for the first time. The first STM experimental results obtained on magnetite in air and in ultrahigh vacuum are reported. Atomic resolution is obtained on Fe3O4 (100) with an ultrahigh vacuum scanning tunneling microscope using iron and tungsten tips. This is the first successful observation of atomic resolution on a ferromagnetic sample using a ferromagnetic tip.
Amorphous Sm(Fe11Ti) ribbons were prepared by melt spinning. After heat treatment, very fine grai... more Amorphous Sm(Fe11Ti) ribbons were prepared by melt spinning. After heat treatment, very fine grains (≊50 nm) of the ThMn12-structure phase were obtained with no signs of a separate intergranular phase. Each grain appears to be a single domain. The maximum room-temperature coercivity is 0.56 T, rising to 1.20 T at 11 K. A model is proposed for the coercivity which is based on an analogy with the random anisotropy model of amorphous magnetism. It gives the correct magnitude of the coercivity, and suggests it should vary as the reciprocal of the crystallite size.
A systematic procedure for producing ZnO nanoparticles by heating ethanol and salt under pressure... more A systematic procedure for producing ZnO nanoparticles by heating ethanol and salt under pressure has been used to make pure ZnO and ZnO doped with cations of all 3d metals from Sc to Cu. When the ZnO is uniformly doped with the 3d cations, the nanoparticles show no ferromagnetism down to 4.2K. However, when the precursors are imperfectly dissolved in ethanol, ferromagnetism is found for Fe, Co, and Ni doping only.
Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions ... more Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions (MTJs) with a tunneling magnetoresistance ratio of up to 330% at room temperature. The lowest normalized noise parameter α of the tunnel barrier reaches 2.5 × 10−12–2.1 × 10−11 μm2, which is comparable to that found in MTJs with the MgO barrier grown by MBE or electron–beam evaporation. This normalized barrier noise is almost bias independent in the voltage range of up to ±1.2 V. The low noise level and high voltage stability may reflect the high quality of the sputtered MgO with a uniform distribution of defects in the MgO layer.
Magnetic properties of thin films of three in-plane alloy systems, namely, Co40Ni40−xCrxB20, Co40... more Magnetic properties of thin films of three in-plane alloy systems, namely, Co40Ni40−xCrxB20, Co40Fe40−xNixB20, and Co40Fe40−xCrxB20 are investigated with a view to reducing the critical current density (jc) for spin transfer torque switching in MgO barrier magnetic tunnel junction nanopillars. In all three systems, the saturation magnetisation, Ms, decreases with increasing Cr or Ni substitution. The Co40Fe40−xCrxB20 alloy system is found to be the best in terms of reducing Ms, while maintaining a high tunnel magnetoresistance ratio. Ferromagnetic resonance experiments revealed that the damping coefficient of CoFeCrB alloy remains unchanged with increasing Cr content, but jc is reduced by a factor of four to 4.9 × 105 A/cm2 by using a Co40Fe32.7Cr7.3B20 free layer while maintaining a magnetoresistance of around 60 %.
In this study thin film samples of Ga1‐xMnxN were grown by pulsed laser deposition on Al2O3 (0001... more In this study thin film samples of Ga1‐xMnxN were grown by pulsed laser deposition on Al2O3 (0001) substrates. X‐ray diffraction measurements have confirmed these thin films exhibit hexagonal wurtzite structure. SQUID measurements show room temperature ferromagnetism of these dilute magnetic semiconductors (DMS). The techniques of X‐ray absorption and soft X‐ray emission spectroscopy at the N K‐edge were used to study the changes in the unoccupied and occupied N 2p partial density of states respectively as a function of dopant concentration. These element and site specific spectroscopies allow us to characterise the electronic structure of these doped materials and reveal the influence of the Mn doping on the valence band as measured through the N 2p partial density of states. X‐ray absorption measurements at the Mn L‐edge confirm significant substitutional doping of Mn into Ga‐sites. Finally, measurements of heavily Mn‐doped films using both soft X‐ray absorption and resonant soft ...
Amorphous melt-spun Pr2(Fe1−xCox)14B has been prepared to test the concept of magnetic-field-indu... more Amorphous melt-spun Pr2(Fe1−xCox)14B has been prepared to test the concept of magnetic-field-induced crystallite alignment. Crystallization temperatures (Tx) of alloys with x=0.5, 0.6, and 1.0 were determined to be 622, 646, and 507 °C, respectively. These temperatures are all lower than the Curie temperatures (Tc) of the crystallized 2:14:1 phase. The glasses were then heat treated at a temperature Tt(Tx<Tt<Tc), either in no field or in a magnetic field of 0.3 T applied parallel to the long edge of the ribbon. The degree of alignment was investigated by means of x-ray diffraction and magnetization measurements. A texture was found where the c axes tend to lie in the ribbon plane in zero field, which is slightly modified when a magnetic field is applied during the heat treatment.
A method for the controlled fabrication of a nickel perpendicular nanocontact with diameters less... more A method for the controlled fabrication of a nickel perpendicular nanocontact with diameters less than 5 nm is reported. The method involves milling pores through the 100 nm thick silicon nitride membrane using a focused ion beam, and depositing thin Ni film on the both side of the silicon nitride membrane. The shape of the resulting pore and nanocontact size is determined by the initial hole size and redeposition of the sputtered material onto the sidewalls of the holes. A sub-5 nm Ni nanocontact was prepared and the I-V and R-H characteristics measured.
Solutions to the main problems in operating a spin-polarized scanning tunneling microscope are di... more Solutions to the main problems in operating a spin-polarized scanning tunneling microscope are discussed. Preliminary experimental results obtained in the course of implementing these solutions are reported. Atomic resolution on Si(111) and Si(100) is achieved with a scanning tunneling microscope (STM) using chromium and iron tips. Fabrication of antiferromagnetic tips of Cr, MnNi, and MnPt is described. A technique of preparation of clean (100) surfaces of Fe3O4 (magnetite) is given. Low-energy electron diffraction patterns were obtained on Fe3O4 for the first time. The first STM experimental results obtained on magnetite in air and in ultrahigh vacuum are reported. Atomic resolution is obtained on Fe3O4 (100) with an ultrahigh vacuum scanning tunneling microscope using iron and tungsten tips. This is the first successful observation of atomic resolution on a ferromagnetic sample using a ferromagnetic tip.
Amorphous Sm(Fe11Ti) ribbons were prepared by melt spinning. After heat treatment, very fine grai... more Amorphous Sm(Fe11Ti) ribbons were prepared by melt spinning. After heat treatment, very fine grains (≊50 nm) of the ThMn12-structure phase were obtained with no signs of a separate intergranular phase. Each grain appears to be a single domain. The maximum room-temperature coercivity is 0.56 T, rising to 1.20 T at 11 K. A model is proposed for the coercivity which is based on an analogy with the random anisotropy model of amorphous magnetism. It gives the correct magnitude of the coercivity, and suggests it should vary as the reciprocal of the crystallite size.
A systematic procedure for producing ZnO nanoparticles by heating ethanol and salt under pressure... more A systematic procedure for producing ZnO nanoparticles by heating ethanol and salt under pressure has been used to make pure ZnO and ZnO doped with cations of all 3d metals from Sc to Cu. When the ZnO is uniformly doped with the 3d cations, the nanoparticles show no ferromagnetism down to 4.2K. However, when the precursors are imperfectly dissolved in ethanol, ferromagnetism is found for Fe, Co, and Ni doping only.
Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions ... more Low frequency 1/f barrier noise has been investigated in sputtered MgO magnetic tunnel junctions (MTJs) with a tunneling magnetoresistance ratio of up to 330% at room temperature. The lowest normalized noise parameter α of the tunnel barrier reaches 2.5 × 10−12–2.1 × 10−11 μm2, which is comparable to that found in MTJs with the MgO barrier grown by MBE or electron–beam evaporation. This normalized barrier noise is almost bias independent in the voltage range of up to ±1.2 V. The low noise level and high voltage stability may reflect the high quality of the sputtered MgO with a uniform distribution of defects in the MgO layer.
Magnetic properties of thin films of three in-plane alloy systems, namely, Co40Ni40−xCrxB20, Co40... more Magnetic properties of thin films of three in-plane alloy systems, namely, Co40Ni40−xCrxB20, Co40Fe40−xNixB20, and Co40Fe40−xCrxB20 are investigated with a view to reducing the critical current density (jc) for spin transfer torque switching in MgO barrier magnetic tunnel junction nanopillars. In all three systems, the saturation magnetisation, Ms, decreases with increasing Cr or Ni substitution. The Co40Fe40−xCrxB20 alloy system is found to be the best in terms of reducing Ms, while maintaining a high tunnel magnetoresistance ratio. Ferromagnetic resonance experiments revealed that the damping coefficient of CoFeCrB alloy remains unchanged with increasing Cr content, but jc is reduced by a factor of four to 4.9 × 105 A/cm2 by using a Co40Fe32.7Cr7.3B20 free layer while maintaining a magnetoresistance of around 60 %.
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