Interlayer exchange coupling and giant magnetoresistance (original) (raw)

Competing Exchange Interactions in Magnetic Multilayers

Physical Review Letters, 2006

We have studied alloying of the nonmagnetic spacer layer with a magnetic material as a method of tuning the interlayer coupling in magnetic multilayers. We have specifically studied the Fe=V100 system by alloying the spacer V with various amounts of Fe. For some Fe concentrations in the spacer, it is possible to create a competition between antiferromagnetic Ruderman-Kittel-Kasuya-Yoshida exchange and direct ferromagnetic exchange coupling. The exchange coupling and transport properties for a large span of systems with different spacer concentrations and thicknesses were calculated and measured experimentally and good agreement between observations and theory was observed. A reduction in magnetoresistance of about 50% was observed close to the switchover from antiferromagnetic to ferromagnetic coupling.

Dependence of the interlayer exchange coupling on the constitution of the magnetic layers

Journal of Applied Physics, 1996

We describe the consequences on the interlayer exchange coupling by the addition of a small amount of Ag impurities within the Co layers of high crystalline quality Co/Cu/Co͑Ag͒ and Cu/ Ru/Co͑Ag͒ trilayers, while maintaining the integrity of the spacer layers. We discuss the consequent changes in the amplitude, period, and phase of the coupling in terms of the modification of interfacial spin-dependent potentials.

Elucidation of the strong effect of an interfacial monolayer on magnetoresistance in giant magnetoresistive devices with current perpendicular to the plane

Physical Review B

Electronic band matching at the interface between ferromagnetic (FM) and nonmagnetic (NM) metals has been considered a key factor that affects the spin-dependent transport properties such as giant magnetoresistance (GMR) effect. However, to date, there has not been an experimental explanation on the effect of a few monolayer atomic structures at the FM/NM interface on the band matching with a direct observation of the atomic-and element-resolved interfacial microstructure. In this study, we fabricated fully epitaxial current-perpendicular-to-plane GMR pseudo-spin-valve (PSV) films of half-metallic Co 2 FeGa 0.5 Ge 0.5 (CFGG)/ Ag spacer/CFGG structure with very thin (0 to 1 nm thick) Ni insertion layers at the CFGG/Ag interfaces. The MR ratio was significantly enhanced (from 23.1% for the PSV without Ni to 32.5% for that) with 0.21 nm-thick Ni insertion. Through an aberration-corrected scanning transmission electron microscopy (STEM), the state-of-the-art atomic-scale microstructure analysis revealed that the Co atoms in a second termination layer from the Ag interface are replaced with Ni monolayer via insertion of 0.21-nm-thick Ni. Our first-principles calculations of ballistic transmittance for the stacking structures modeled by the STEM images indicated that substituting the Co termination layer with Ni improved electronic band matching of majority spin electrons. This study proves that even a monolayer near the interface critically affects the interfacial band matching and MR properties.

Exchange Coupling in Magnetic Semiconductor Multilayers and Superlattices

Acta Physica Polonica A, 2012

The study of ferromagnetic semiconductors continues to be of great interest because of their potential for spintronic devices. While there has been much progress in our understanding of ferromagnetic semiconductor materials particularly of the canonical IIIV system Ga1−xMnxAs many issues still remain unresolved. One of these is the nature of interlayer exchange coupling in GaMnAs-based multilayers, an issue that is important from the point of view of possible spintronic applications. In this connection, it is important to establish under what conditions the interlayer exchange coupling between successive GaMnAs layers is antiferromagnetic or ferromagnetic, since manipulation of such interlayer exchange coupling can then be directly applied to achieve giant magnetoresistance and other devices based on this material. In this review we will describe magneto-transport, magnetization, and neutron reectometry experiments applied to two types of GaMnAs-based multilayer structures superlattices and tri-layers consisting of GaMnAs layers separated by non-magnetic GaAs spacers. These measurements serve to identify conditions under which AFM coupling will occur in such GaMnAs/GaAs multilayer systems, thus providing us the information which can be used for manipulating magnetization (and thus also giant magnetoresistance) in structures based on the ferromagnetic semiconductor GaMnAs.

Calculations of giant magnetoresistance in Fe/Cr trilayers using layer potentials determined from ab initio methods

Journal of Physics: Condensed Matter, 2007

The ab initio full-potential linearized augmented plane-wave method explicitly designed for the slab geometry was employed to elucidate the physical origin of the layer potentials for the trilayers nFe/3Cr/nFe(001), where n is the number of Fe monolayers. The thickness of the transition-metal ferromagnet has been ranged from n = 1 up to n = 8 while the spacer thickness was fixed to 3 monolayers. The calculated potentials were inserted in the Fuchs-Sondheimer formalism in order to calculate the giant magnetoresistance (GMR) ratio. The predicted GMR ratio was compared with the experiment and the oscillatory behavior of the GMR as a function of the ferromagnetic layer thickness was discussed in the context of the layer potentials. The reported results confirm that the interface monolayers play a dominant role in the intrinsic GMR.

First-Principles Calculations of Magnetic Interfaces and Multilayers

Magnetic Multilayers, 1994

We present a method to calculate the effective exchange interaction parameters based on the realistic electronic structure of correlated magnetic crystals in local approach with the frequency dependent self-energy. The analog of ''local force theorem'' in the density-functional theory is proven for highly correlated systems. The expressions for effective exchange parameters, Dzialoshinskii-Moriya interaction, and magnetic anisotropy are derived. The first-principles calculations of magnetic excitation spectrum for ferromagnetic iron, with the local correlation effects from the numerically exact QMC scheme, are presented.

General Green’s-function formalism for transport calculations withspdHamiltonians and giant magnetoresistance in Co- and Ni-based magnetic multilayers

Physical Review B

A novel, general Green's function technique for elastic spin-dependent transport calculations is presented, which (i) scales linearly with system size and (ii) allows straightforward application to general tight-binding Hamiltonians (spd in the present work). The method is applied to studies of conductance and giant magnetoresistance (GMR) of magnetic multilayers in CPP (current perpendicular to planes) geometry in the limit of large coherence length. The magnetic materials considered are Co and Ni, with various non-magnetic materials from the 3d, 4d, and 5d transition metal series. Realistic tight-binding models for them have been constructed with the use of density functional calculations. We have identified three qualitatively different cases which depend on whether or not the bands (densities of states) of a non-magnetic metal (i) form an almost perfect match with one of spin sub-bands of the magnetic metal (as in Cu/Co spin valves); (ii) have almost pure sp character at the

Calculation of Giant Magnetoresistance in Laterally Confined Multilayers

1997

We have studied the Giant Magnetoresistance (GMR) for laterally confined multilayers, e.g., layers of wires, using the classical Boltzmann equation in the current-in-plane (CIP) geometry. For spin-independent specularity factors at the sides of the wires we find that the GMR due to bulk and surface scattering decreases with lateral confinement. The length scale at which this occurs is of order the film thickness and the mean free paths. The precise prefactor depends on the relative importance of surface and bulk scattering anisotropies. For spin-dependent specularity factors at the sides of the wires the GMR can increase in some cases with decreasing width. The origin of the change in the GMR in both cases can be understood in terms of lateral confinement changing the e#ective mean free paths within the layers. PACS numbers: 75.70.-i, 75.70.Cn, 75.70.Pa, 72.15.Gd, 73.50.-h Typeset using REVT E X I. INTRODUCTION Electrical transport properties of magnetic multilayers, which are thin ...