Quantitative investigation of FeMn-based spin-valves by rotating field magnetoresistance measurements (original) (raw)
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Rotating-field magnetoresistance of exchange-biased spin valves
Journal of Applied Physics, 2005
We investigate the magnetoresistance (MR) of spin valves by (i) varying the strength of the field applied in a fixed direction and (ii) rotating the field with fixed strength. The latter data reflect in general a mixture of giant and anisotropic magnetoresistance (GMR and AMR). We present an experimental procedure to suppress the AMR contributions of all ferromagnetic layers in the spin valve without disturbing the GMR response. The resulting angular MR curves are fitted with a single-domain model to determine with high precision the exchange bias field, the uniaxial anisotropies, the GMR ratio, and the interlayer coupling field. The application of the method to differently prepared Ta͑5.0 nm͒ / NiFe͑3.0 nm͒ / FeMn͑15.5 nm͒ / NiFe͑3.0 nm͒ /Co͑2.0 nm͒ / Cu͑3.5 nm͒ /Co͑2.0 nm͒ / NiFe͑7.0 nm͒ spin valves with GMR ratios of 1.8% and 4% demonstrates the sensitivity and reveals differences of the order of a few percents of the exchange bias field for the uniaxial anisotropy fields of the free and pinned layer as well as for the interlayer coupling field.
Magnetoresistance values exceeding 21% in symmetric spin valves
Journal of Applied Physics, 1995
We report values of the giant magnetoresistance (GMR) effect exceeding 21% in symmetric spin valves, the highest values ever reported for such structures. The key elements in this achievement are the use of a Co/CuKo/Cu/Co multilayer in which the center Co layer is substantially thicker than the outer Co layers and the use of the antiferromagnetic insulator NiO at the top and bottom to pin the adjacent Co layers magnetically. The relative Co layer thicknesses suggest that some specular scattering of conduction electrons may occur at the metal/insulator interfaces and may enhance the GMR. 0 1995 American Institute of Physics.
IEEE Transactions on Magnetics, 2008
Switching characteristics and magnetoresistance of spin valves with perpendicular anisotropy based on Co-Fe/Pd multilayers deposited by ultrahigh vacuum (UHV) sputtering have been studied. In unpatterned thin films without exchange bias, high current-in-plane giant magnetoresistance (CIP-GMR) of 9.7% and 15.2% in single-spin valves (SSVs) and dual-spin valves (DSVs) was measured, a significant improvement over previous work. We describe the effects of a Ta seed layer and postdeposition annealing on the perpendicular anisotropy and magnetoresistance of Co-Fe/Pd spin valves, which can be attributed to improvements in the fcc (111) orientation of Pd and the formation of Co-Pd alloys at the Co-Fe/Pd interfaces, respectively. We also show that the coercivity of the layers can be tuned by varying the Co-Fe alloy composition in the multilayers, and describe the minor loops of perpendicular DSVs that exhibit four distinct resistance states, which is a potential structure for multistate storage devices.
Inverse spin-valve-type magnetoresistance in spin engineered multilayered structures
Physical Review Letters, 1994
The resistivity of magnetic multilayers is generally smaller when the magnetizations of successive layers are parallel, which is the so-called giant magnetoresistance or spin-valve effect. %'e have been able to reverse this eA'ect and to obtain a smaller resistivity for an antiparallel arrangement by intercalating thin Cr layers within half of the Fe layers in Fe/Cu multilayers. This inverse spin-valve elfect is due to the inverse spin asymmetries of the electron scattering in successive Fe layers with and without Cr. This is a confirmation of the fundamental mechanism of the giant magnetoresistance.
Negative magnetoresistance in Fe 3 O 4∕ Au∕ Fe spin valves
The structural, electrical, and magnetic properties of Fe 3 O 4 / Au/ Fe spin valves on MgO͑001͒ are presented. In contrast to more conventional spin valve structures, the current-in-plane resistance of the Fe 3 O 4 / Au/ Fe spin valves is found to be smallest for an antiparallel alignment of the magnetization of the Fe 3 O 4 and Fe layer. Since the electrical current is transported through the low resistance Au and Fe layers, the negative magnetoresistance effect is attributed to an inverse electron spin scattering asymmetry at the Fe 3 O 4 / Au interface.
Exchange-biased spin valves with perpendicular magnetic anisotropy based on (Co/Pt) multilayers
Journal of Applied Physics, 2003
We have prepared spin valves exhibiting perpendicular magnetic anisotropy ͓perpendicular spin valves ͑PSVs͔͒ by sputtering. These PSVs associate a ''free'' ͑Co/Pt͒ multilayer with a ''pinned'' ͑Co/Pt͒/FeMn multilayer separated by various spacer materials ͑Pt, Cu, Al 2 O 3 ). We carried out a comprehensive study of the magnetic and magnetotransport properties of the biased multilayers and of the complete spin valves. When the number of repeats in the ͑Co/Pt͒ exchange-biased multilayer is larger than 3, the samples present 100% remnant magnetization in the perpendicular configuration. The major hysteresis cycles exhibit two well-separated loops associated with the free and the exchange-biased ͑Pt/Co͒ multilayers. When optimized, the exchange-bias field can be larger than the coercivity of the pinned layer. Metallic PSVs with Cu spacers exhibit giant magnetoresistance but the amplitude is only of the order of 1% due to significant current shunting. In contrast, perpendicularly magnetized tunnel junctions are very promising.
Journal of Applied Physics, 2010
NiMn is an interesting material for achieving a high exchange bias in spin valve systems. We investigated the influence of a nano-oxide layer ͑NOL͒ inserted in the pinned Co layer on the magnetotransport properties of NiMn/Co/Cu/Co spin valve sensors. The samples were annealed at 350°C for 10 min to achieve the antiferromagnetic L1 0 ordered structure of NiMn. The NOL has been characterized by small angle x-ray reflectivity, transmission electron microscopy ͑TEM͒, and energy filtered TEM. The inclusion of the NOL leads to an increase in the giant magnetoresistance ͑GMR͒ by 20 % indicating a high degree of specular reflection at the NOL. For NOL positions close to the NiMn/Co interface, a decrease in the exchange bias field ͑H ex ͒ is observed. The best combination of high GMR value and large H ex was found when the NOL was inserted in the center of the pinned Co layer.
Temperature dependence of giant magnetoresistance properties of NiMn pinned spin valves
Journal of applied physics, 1998
The giant magnetoresistance response of NiMn pinned spin valves was studied at elevated temperature. Top spin valve films were made by ion beam sputtering and thermally treated to induce the strong unidirectional pinning field in the pinned layer. Both δR and δR/R decrease linearly with temperature. The sheet resistance of the spin valves also increases linearly with temperature. The exchange coupling between pinned layer and free layer decreases slightly and the coercivity of the free layer increases slightly. The temperature dependence of the exchange pinning field is unique in NiMn spin valves. The pinning field has a weakly increasing temperature dependence up to 200 °C, then decreases to zero at the blocking temperature of 380 °C. Samples with different thickness NiMn layers show different temperature dependencies. However, the blocking temperature is unchanged. The pinning fields of NiMn, FeMn, IrMn, and NiO spin valves were also measured up to 200 °C NiMn pinned spin valves show the least dependence of pinning field at elevated temperatures.