Interface resistance of disordered magnetic multilayers

Abstract

We study the effect of interface disorder on the spin-dependent interface resistances of Co/Cu, Fe/Cr, and Au/Ag multilayers using a newly developed method for calculating transmission matrices from first-principles. The efficient implementation using tight-binding linear-muffin-tin orbitals allows us to model interface disorder using large lateral supercells whereby specular and diffuse scattering are treated on an equal footing. Without introducing any free parameters, quantitative agreement with experiment is obtained. We predict that disorder reduces the majority-spin interface resistance of Fe/Cr͑100͒ multilayers by a factor 3. When two layers of magnetic material are separated by a non-magnetic spacer layer, the electrical resistance of the system depends strongly on whether the magnetization directions are aligned parallel or antiparallel. This effect is known as giant magnetoresistance ͑GMR͒. 1 The huge interest 2-4 in the physics of GMR is largely driven by the wide application potential of the effect, which has already been realized in magnetic recording heads.GMR can be observed in a number of different measuring configurations. The current-in-plane ͑CIP͒ configuration is experimentally the simplest and is what is used at present in applications. However, for gaining a better understanding of the underlying physics, the current-perpendicular-to-theplane ͑CPP͒ configuration 3,5-9 is preferred because of its higher symmetry, which should make it easier to understand, and because of higher MR ratios.The factors usually considered in theoretical treatments of GMR are the potential steps encountered by electrons passing from one material to another, impurity scattering in the bulk of the layers, and defect scattering at the interfaces. [2][3][4] There has been a great deal of discussion about the relative importance of these ingredients and their spin dependence, which cannot be resolved solely on the basis of model calculations which include these effects in parametrized form. Once the question has been suitably posed, however, detailed electronic structure calculations can be used to resolve the issue quantitatively. For example, the effect of potential steps and their microscopic origin could be established in this way. 10,11 In this paper we wish to address the relative role of specular and diffuse interface scattering. This has been studied by a large number of authors but so far only using simple models which do not allow for detailed quantitative analysis of specific materials. 12,13 We focus on the interface resistance of the resistor model which describes the observed thickness and layer dependence of CPP-GMR remarkably well. 3 Because it turns out to be strongly spin dependent and dominates the magnetoresistance for layer thicknesses which are not too large, the key to understanding CPP magnetoresistance lies in understanding the origin of the interface resistance. The methodology which we have developed allows us to include specular and diffuse scattering on an equal footing without introducing ...

Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids

“…The theory is valid under two conditions: ͑i͒ the system should be diffuse, i.e., the elastic mean free path ᐉ ͑including scattering at interfaces͒ should be smaller than typical sample scales and ͑ii͒ the ferromagnetic elements should have an exchange splitting ⌬, which is large enough that the magnetic coherence length ᐉ c ϭប/ͱ2m⌬ Ͻmin(ᐉd F ), where d F is the thickness of the ferromagnetic layer. These conditions are usually fulfilled in transitionmetal systems: Deviations from diffuse behavior, such as quantum-size effects and breakdown of the series resistor model, are small or controversial, 20,24 whereas the magnetic coherence length is of the same order as the lattice constant in high-T c transition-metal ferromagnets. 10,25 We obtain identical results by two methods: The first one is a combination of the Boltzmann-like method of Schep et al 18 for collinear systems and the random-matrix theory of Waintal et al 14 The second one is an extension of magnetoelectronic circuit theory 6 to arbitrary resistors.…”

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

“…Moreover, according to Xia et al 37 g ↑↓ / A Ӎ 5·10 14 ⍀ −1 m −2 . For a quantitative assessment of the relations ͑5͒ and ͑9͒ we assume Ϸ 5°͑sin 2 = 0.01͒ and =10 11 s −1 ͑ប =65 eV͒.…”

Enhanced Gilbert Damping in Thin Ferromagnetic Films

“…The spin polarization of electrons emitted by Py has been measured to be p ഠ 0.4 in point contacts [19], the magnetization per atom is f ഠ 1.2, and the Landé factor is g L ഠ 2.1 [12]. The interface conductance of metallic interfaces with Fe or Co is of the order of 10 15 V 21 m 22 , with significant but not drastic dependences on interface morphology or material combination [20]. This corresponds to roughly one conducting channel per interface atom.…”

“…His expression for the damping coefficient [Eq. (20) in Ref. [9] ] scales like ours as a function of layer thickness, but differs as a function of material parameters.…”