Giant Magnetoresistance Calculated From First Principles
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Giant Magnetoresistance Calculated From First Principles W. H. Butler* , James M. MacLaren ** and X.-G.Zhangt *Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6114 -5Department of Physics, Tulane University, New Orleans, Louisiana 70118 tCenter for Computational Sciences, University of Kentucky, Lexington, Kentucky 40506-
0045 ABSTRACT The Layer Korringa Kohn Rostoker-Coherent Potential Approximation technique was used to calculate the low temperature Giant Magnetoresistance from first principles for ColCu and permalloylCu superlattices. Our calculations predict large giant magnetoresistance ratios for ColCu and extremely large ratios for permalloyjCu for current perpendicular to the layers. Mechanisms such as spin-orbit coupling which mix spin channels are expected to greatly reduce the GMR effect for permalloyfCu.
Introduction An unexpectedly large effect of an applied magnetic field on the electrical resistance has been observed in a number of multilayer systems involving transition metals. The effect consists of a dramatic decrease in the electrical resistance in the presence of an applied magnetic field and has been observed in Fe-Cr multi-layers[l, 2, 3, 4, 5, 6], in Co-Cu multilayers[3, 4, 7], in Co-Ru multilayers[3], and in bi-layers of Ni.8Fe.2 separated by a thin layer of Cu[7, 8]. The effect is seen in systems in which alternate layers of magnetic atoms are aligned anti-parallel with one another in the absence of the applied field. Application of the magnetic field brings the layers into alignment and causes a decrease in the electrical resistivity both parallel to the layers and perpendicular to them. The resistances of bcc (100)Fel(100)Cr[1] and fcc (11l)Coj(1ll)Cu[4] have been observed to decrease by almost a factor of two when an applied magnetic field brings the magnetic moments on the layers into alignment. In this paper we present calculations of this giant magnetoresistance effect directly from first principles.
Previous Theory Baibich et. al.[1] who first reported the effect based on their observations on Fe-Cr multi-layer systems observed that dilute Cr impurities in bulk Fe scatter majority spin electrons much more strongly than minority spin electrons. They proposed that the Cr atoms in the spacer layers might act the same way leading to a low resistance for the down spin electrons when the layers are aligned in parallel. The anti-parallel alignment would, in this picture, lead to a higher resistance by mixing the spin channels. Binasch et. al.[2] described the effect in terms of the necessity for electrons to undergo spin-flip scattering when traveling from one Fe layer into an adjacent one when the layers were aligned anti-parallel. Camely and Barnag and Barna.4 et. al.19, 10] generalized the semi-classical Boltzmann theory approach of Fuchs[ll] and Sondheimer[12] to treat layered systems with different scattering properties in the two spin channels. Levy et. al.[13] and Zhang and Levy[14] developed a quantum mechanical treatment for spin dependent scatte
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