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ABSTRACT The cylindrical cathode vacuum arc deposition method is used to produce pure Cr films on SiO2/Si(100) substrates. Deposition and implantation of Fe into the films were performed to study the influence of these processes on the... more
ABSTRACT The cylindrical cathode vacuum arc deposition method is used to produce pure Cr films on SiO2/Si(100) substrates. Deposition and implantation of Fe into the films were performed to study the influence of these processes on the structure of Cr. X-ray diffraction and cross-sectional transmission electron microscopy analyses are performed to establish the effects of spinodal decomposition in these materials.
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Magnetic properties of NiMn2−xCoxO4 spinel oxides have been investigated. The paramagnetic moment shows a direct correlation with the nominal cation concentration. A first transition, from paramagnetism to ferrimagnetism, occurs at high... more
Magnetic properties of NiMn2−xCoxO4 spinel oxides have been investigated. The paramagnetic moment shows a direct correlation with the nominal cation concentration. A first transition, from paramagnetism to ferrimagnetism, occurs at high temperature, going from Tc=125K (NiMn1.8Co0.2O4) up to 210K. A second transition is observed at lower temperature. It takes place at about 60K and increases with Co content up to
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We present a simple criterion to evaluate the portion of the magnetoresistance (in both multilayers and granular magnetic materials) that arises from antiferromagnetic coupling. This criterion is applied to Co/Ag samples that undergo a... more
We present a simple criterion to evaluate the portion of the magnetoresistance (in both multilayers and granular magnetic materials) that arises from antiferromagnetic coupling. This criterion is applied to Co/Ag samples that undergo a transformation between the multilayer and ...
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ABSTRACT Granular ribbons of composition Co10Cu90 show giant magnetoresistance (GMR) when heat treated. In order to understand the kinetics of the transformation of the original ribbons into the aggregate with a Co cluster distribution,... more
ABSTRACT Granular ribbons of composition Co10Cu90 show giant magnetoresistance (GMR) when heat treated. In order to understand the kinetics of the transformation of the original ribbons into the aggregate with a Co cluster distribution, we have measured the resistivity of these materials during anneals at different heating rates. These anneals show a clear two step process, associated to transformations related to the Co (or Co-rich) grains. The hysteresis curves and magnetoresistance for these samples, measured at room temperature, show a clear change in size for the magnetic grains considering superparamagnetic interactions. The dependence of the magnetoresistence on the magnetization is investigated using a a model developed by taking explicitly into consideration the magnetic moment distribution and the spin-dependent scattering at the interfaces and within the grains. Fits to a pure superparamagnetic model show that the expected dependence of the GMR with the square of the magnetization is not followed. We have also measured, at low temperatures, the thermopower, and resistivity of these alloys at different stages of the annealing process. The low temperature resistivity shows a distinct minimum around 20 K for the “as-made sample, which disappears upon annealing at even the lowest stages.
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We have studied the electrical resistivity and giant magnetoresistance (GMR) of (Co(15 As )/Ag(45 As )) 20 /Ag(45 As ) multilayers treated at di!erent annealing temperatures. A simulation based on a formal solution of the Boltzmann... more
We have studied the electrical resistivity and giant magnetoresistance (GMR) of (Co(15 As )/Ag(45 As )) 20 /Ag(45 As ) multilayers treated at di!erent annealing temperatures. A simulation based on a formal solution of the Boltzmann equation for the electrical resistivity was performed, and the results compared to the experimental results from 4.2 to 300 K. The simulation shows that
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Bol. Soc. Esp. Ceram. Vidrio, 2008, 47, 178-182
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ABSTRACTWe recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices grown by MBE. The magnetoresistance is found to be very large for thin Cr layers. We ascribe this magnetoresistance to a... more
ABSTRACTWe recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices grown by MBE. The magnetoresistance is found to be very large for thin Cr layers. We ascribe this magnetoresistance to a magnetic gate effect.We recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices with thin Cr layers [1]. A large magnetoresitance has also been observed in Fe/Cr/Fe sandwhiches [2]. In both cases, for Cr layers thinner than about 30 Å an antiparallel coupling of the magnetization of neighbor Fe layers is indicated by magnetic, magneto-optic and light scattering measurements [1–3]. It thus turns out that the large magnetoresistance os associated with the change to parallel alignment in an applied field. In this paper, we present new data on the magnetic and transport properties of Fe/Cr superlattics and we concentrate on the discussion of the microscopic origin of the magnetoresistance
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ABSTRACT The authors have built an inexpensive AC synchronous detector for measuring conductances between 5 mu S and 1 S. This allows the measurement and control of low temperatures using carbon glass, Ge or similar resistors with... more
ABSTRACT The authors have built an inexpensive AC synchronous detector for measuring conductances between 5 mu S and 1 S. This allows the measurement and control of low temperatures using carbon glass, Ge or similar resistors with precision to within the standard temperature calibration resolution (+or-0.1%). Simple modifications that improve stability and response time are presented, which enable the instrument to be used to measure changes in the conductivity of metallic films during deposition and of polymers under ion bombardment.
... The discrepancies in r,, seen between the isothermal method and Kissinger's method may be attributed to the contribution of an incubation time (t,J which is not taken into account in the traditional Johnson-Mehl-Avrami... more
... The discrepancies in r,, seen between the isothermal method and Kissinger's method may be attributed to the contribution of an incubation time (t,J which is not taken into account in the traditional Johnson-Mehl-Avrami expression. Page 8. Crystallisation of metallic glusses ... Anul. ...
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The relation between giant magnetoresistance (GMR) and phase separated nanostructures in Cu90Co10 is studied using magnetotransport measurements together with transmission electron microscopy and x-ray microanalysis. The samples were... more
The relation between giant magnetoresistance (GMR) and phase separated nanostructures in Cu90Co10 is studied using magnetotransport measurements together with transmission electron microscopy and x-ray microanalysis. The samples were melt-spun ribbons isochronally annealed up to 873 K, and all show in their grains a homogeneous spinodal decomposition characterized by long parallel Co-excess stripes. These stripes have 40-nm modulation periods and develop
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© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ... Structural and physical properties of spinel-type NiMn2xCoxO4 oxides ... O. Peña*, 1, Yanwei Ma1, M. Bahout1, P. Durán2, C. Moure2, MN Baibich3, and G. Martinez3 1 LCSIM, UMR... more
© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ... Structural and physical properties of spinel-type NiMn2xCoxO4 oxides ... O. Peña*, 1, Yanwei Ma1, M. Bahout1, P. Durán2, C. Moure2, MN Baibich3, and G. Martinez3 1 LCSIM, UMR 6511, CNRS - Université de ...
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... Phys. Rev. B, 60 (1999), p. 7006. [9] JM De Teresa, C. Ritter, MR Ibarra, PA Algarabel, JL Garcia-Mu??oz, J. Blasco, J. Garcia and C. Marquina. Phys. Rev. B, 56 (1997), p. 3317. Corresponding Author Contact Information Corresponding... more
... Phys. Rev. B, 60 (1999), p. 7006. [9] JM De Teresa, C. Ritter, MR Ibarra, PA Algarabel, JL Garcia-Mu??oz, J. Blasco, J. Garcia and C. Marquina. Phys. Rev. B, 56 (1997), p. 3317. Corresponding Author Contact Information Corresponding author. ...
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ABSTRACT The exchange-bias effect was investigated through the analyses of the magnetic hysteresis loops and anisotropic magnetoresistance measurements of NiFe/FeMn bilayers. The angular variations of the exchange-bias field and... more
ABSTRACT The exchange-bias effect was investigated through the analyses of the magnetic hysteresis loops and anisotropic magnetoresistance measurements of NiFe/FeMn bilayers. The angular variations of the exchange-bias field and coercivity were fitted in the framework of a domain-wall formation model which assumes formation of a planar domain wall at the antiferromagnetic side of the interface. The anisotropy parameters of both layers were extracted from the fits and were also used to obtain the orientation of the NiFe magnetization for different magnetic field in-plane directions. The angular dependence of the anisotropic magnetoresistance was then calculated and a comparison with the experimental measurements was made. The agreement between these curves was good for magnetic field much higher than the exchange-bias field and only reasonable for magnetic field of the order of or lower than the exchange-bias field.
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We studied the microstructural transformations of Co10Cu90 ribbons by analyzing the in situ resistivity versus temperature, the giant magnetoresistance (GMR) and Transmission Electron Microscopy (TEM) images for isochronous treatments... more
We studied the microstructural transformations of Co10Cu90 ribbons by analyzing the in situ resistivity versus temperature, the giant magnetoresistance (GMR) and Transmission Electron Microscopy (TEM) images for isochronous treatments interrupted at different temperatures Tf=494–873K. Resistivity results indicate that several processes take place during the annealing and they should relate to the changes in GMR. The largest GMR (25% at 4.2K)