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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Calculation of the magnetorefractive effect in giant magnetoresistive granular films

V. G. Kravets, D. Bozec, J. A. D. Matthew, and S. M. Thompson

J. Appl. Phys. 91, 8587 (2002); http://dx.doi.org/10.1063/1.1447299 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2002

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Calculations of the magnetorefractive (MRE) effect in giant magnetoresistive CoxAg1−x (GMR) granular films have been performed and compared with experimental data. At long wavelengths (λ>20 μm), there is a linear relationship between the GMR and MRE. As the wavelength is reduced (10<λ<20 μm), the value of ωτ↑(↓) becomes increasingly important requiring fitting of the spin dependent relaxation times. For λ<10 μm, optical constants such as εr become significant and the MRE curve becomes more complex. Spin dependence was introduced by modeling the optical conductivity using the model of Zhang and Levy. Both the calculation and experiment reveal that the MRE effect is an order of magnitude larger for s-polarized light than for p-polarized light at high angles of incidence. © 2002 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
75.47.De Giant magnetoresistance
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
78.20.Ls Magneto-optical effects

High-field magnetoresistance, giant magnetoresistance, and superparamagnetism in Co/Cu multilayers

D. Elefant, D. Tietjen, R. Schaefer, D. Eckert, R. Kaltofen, M. Mertig, and C. M. Schneider

J. Appl. Phys. 91, 8590 (2002); http://dx.doi.org/10.1063/1.1451890 (3 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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High-field magnetoresistance (HMR) in fields up to μ0H=16 T was measured on dc magnetron sputtered Co/Cu multilayers (MLs) with tCu=0.6–1.1 nm and tCo=0.3–4 nm, in the temperature range T=4.2–300 K. With decreasing single layer thickness the HMR at 300 K exceeds 10% and it is far from saturation up to μ0H=16 T. Independent of the HMR in the low field region μ0H⩽3 T a strongly Cu layer dependent GMR=0–60% is observed. Decreasing the temperature below 150 K down to 4.2 K the HMR changes into a GMR type field dependence with pronounced saturation. The superparamagnetic-like HMR dependence on H and T for high temperatures does not scale with H/T. Kerr microscopy on MLs, showing both HMR and GMR, reveals ferromagnetically and antiferromagnetically coupled domains, whereas in MLs showing HMR but not GMR only large ferromagnetic domains are visible. The results, including magnetization and roughness measurements, suggest the existence of very small Co clusters (almost in the atomic scale) with canted magnetic moments, causing the HMR to be independent of the antiferromagnetic and ferromagnetic coupling of the Co layers, respectively. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
78.66.Bz Metals and metallic alloys

Observation of magnetoresistance in core–shell Fe–Fe oxide systems

L. Savini, E. Bonetti, L. Del Bianco, L. Pasquini, S. Signoretti, P. Allia, M. Coisson, J. Moya, V. Selvaggini, P. Tiberto, and F. Vinai

J. Appl. Phys. 91, 8593 (2002); http://dx.doi.org/10.1063/1.1447300 (3 pages) | Cited 12 times

Online Publication Date: 13 May 2002

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A negative magnetoresistance was measured between 15 and 300 K under a maximum field H=70 kOe on two granular systems obtained by compacting Fe nanoparticles surrounded by an oxide shell ∼2 nm thick. The effect depended on the Fe core average size D that was of 8 and 18 nm in the two samples, as by x-ray diffraction. The maximum relative resistance change, about 5%, was observed at 50 K in the sample with smaller D. The results have been interpreted considering intraparticle and interparticle magnetic correlations and microscopic mechanisms similar to those responsible for the magnetoresistance in other granular systems. © 2002 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Correlation among the structural and magnetic properties of CoCu granular alloys

A. García Prieto, M. L. Fdez-Gubieda, C. Meneghini, and A. García-Arribas

J. Appl. Phys. 91, 8596 (2002); http://dx.doi.org/10.1063/1.1451891 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2002

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We have analyzed the magnetic and structural properties of CoCu melt-spun granular alloys annealed at increasing temperatures by means of their room-temperature hysteresis loops and high resolution x-ray diffraction (XRD) experiments. The magnetic analysis has been performed taking into account two contributions to the total magnetization: one from superparamagnetic nanometer Co clusters responsible also of the giant magnetoresistance (GMR) and another ferromagnetic; originated by a Co-rich phase observed by XRD. We have also detected a percentage of Co that remains diluted into the Cu matrix at high annealing temperatures (Tann⩾500 °C) due to the mixcibility of Co and Cu at those temperatures, and this is in the origin of the drop of the GMR. © 2002 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing
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