Study on electronic structure and magnetic properties of Ni 3 Fe ferromagnetic layer adjacent to Cu
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The effect of a Cu layer on the electronic structure and magnetic properties of Ni3Fe was studied by employing the discrete-variational method in the framework of density-functional theory. Three models were established for Ni3Fe(6), Ni3Fe(3)/Cu(3)/Ni3Fe(3), and Ni3Fe(3)/Cu(3). The charge transfer, magnetic moment, and spin exchange split at the Fermi level were obtained for Fe and Ni atoms in a Ni3Fe layer. The related characterizations of Ni3Fe were estimated from those of Fe and Ni atoms. It was discovered that the magnetic properties of the Ni3Fe layer improved when adjacent to Cu layer due to the improvement of the corresponding properties of the Fe atoms in the Ni3Fe. However, the magnetic moment and the spin exchange split of the Ni atoms in the Ni3Fe decreased when the Ni3Fe was adjacent to a Cu layer.
I. INTRODUCTION
Research on spin valves with Co or NiFe as ferromagnetic layers, because of their good low switching properties and high sensitivities, have attracted a great deal of interest both for their fundamental significance and for practical applications as elements of magnetic recording head and sensors, etc.1–3 The system that has been most extensively investigated is one of (NiFe or Co)/NM/NiFe trilayers produced by direct current (dc) sputtering.4–7 Here NM stands for nonmagnetic layers. The differential switching for the two ferromagnetic layers in this simple configuration can be realized by their different coercive fields because the coercivity is dependent on magnetic materials and on layer thicknesses. Experimental results show that the nonmagnetic layers play a significant role in obtaining a magnetoresistance effect in the trilayer systems. It is reported that the largest magnetoresistance effect has been observed in Co/Cu superlattice.8,9 In contrast to this, Ta and Ru layers, for instance, are known to be unfavorable for obtaining the GMR when compared to Cu.10,11 From the theoretical point of view, many studies have been performed on the microscopic origin of the influence of nonmagnetic layers on Co ferromagnetic layer. For instance, Kai et al.12 have found that MR ratio of Co/X superlattices (X ⳱ Cu, Ru, Rh, and Pd) varies to a large extent with different nonmagnetic layers due to their influence on the electronic structure of the Co layer.
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II. CALCULATION METHOD AND MODELS A. Calculation method
The discrete-variational method (DVM) of densityfunctional theory in the framework of the local spindensity approximation14–18 has been used to study the
DOI: 10.1557/JMR.2005.0025 36
However, the influence of Cu on the NiFe alloy ferromagnetic layer has not been systematically studied from microscopic perspectives. It is well known that the NiFe layer is of essence in obtaining a spin valve with high sensitivity due to its soft magnetic properties, as mentioned above. Therefore, study on the effect of Cu layer on the electronic structure and magnetic properties of NiFe layer can provide a theoretical insight into microscopic origin related to the GMR effect i
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