Giant magnetoresistance in ultra-thin layers

Abstract

We consider the transport properties in magnetic ultra-thin multilayers for electronic current in the plane of the surfaces. In the case of ultra-thin films, the conduction electron transport behavior is influenced by the shape and the thickness of a sample. The boundary conditions at the surface and interfaces lead to the electric charge density distribution across a film. We discuss the influence of sample thickness on some electronic properties like the Fermi energy, distribution of electrons and their spin polarisation. We justify some parameters introduced to the model potential whose values for spacer and ferromagnetic metals depend on the layer thickness. In this aspect the present approach constitutes improvement of Hood-Falicov model for the case of very thin layers.The discovery of giant magnetoresistance effects in Fe/Cr multilayers [1, 2] has triggered a large number of studies on the transport properties of magnetic multilayers. In spite of many experimental and theoretical investigations the description of the phenomenon is not completed and makes a challenge for many researchers [e.g. 3, 4]. In our paper [5] we have considered the transport properties in magnetic multilayers for electronic current in the layers parallel to the surfaces. This model is based on the effective s-band construction for the multilayer consisted of the spacer metallic and ferromagnetic, including s-d coupling, layers. In that model we have taken into account the spectrum energy of electrons in a trilayer and we have made the calculations of the Fermi level which is common for the effective s band electrons in tim whole sample [5]. The standard approach is determined by treating all of the valence electrons as being in a single free-electron like band with an isotropic effective mass, in each layer, i.e. spacer and ferromagnetic layer separately. In this paper we assume that a considered sample has a structure of three thin films which are characterised by means of the effective potentials reflecting the multilayered structure. Each of layers has got a crystal structure and the electronic density distribution is connected with the electric potential in a crystal assumed as a superposition of one-electronic potentials produced at the lattice sites. These sites are labeled by the two-dimensional vector j determined in the v-th layer parallel to the crystallographic plane and to the fihn surfaces. Each of n planes (v E (1, n)) *) Presented at ll

Role of Spin Mixing at Interface

“…We analysed also the variation of MDP in heterostructure bilayer systems [21]. Below, we show the contribution of the variation of MDP across the magnetic-nonmagnetic D218 Role of spin mixing at interface trilayer structure and the interface spin-mixing influence on GMR effects obtained by the Boltzmann equation in the frame of the extended Hood-Falicov theory presented in [22,23]. The variation of the potential in trilayer structure is presented in Fig.…”

“…The dots represent the value of potential in plane ν (the solid curve is for visualisation). Taking into account the potential distribution in thin layers we should introduce the summation over discrete spectrum of layers ν instead of the integration with respect to z inside the thickness interval [22]. The local magnetoresistance can be then calculated in the following way: M R = ν (σ ↑↑ (ν) − σ ↑↓ (ν))/ ν σ ↑↑ (ν), where σ ↑↓ (ν) and σ ↑↑ (ν) stand for the conductivity in the case of antiparallel and parallel magnetization of the cover layers, respectively.…”

“…Similarly, the usual integration over z for calculating MR we take into account the summation over ν. In the case of ultra-thin films they are given by the sum of the conductivities of two channels of the electrons with two spin orientation [22]. For the sake of simplicity we supposed that the values of the electronic density n i (for i = 1, 2, 3) and the effective mass m iσ (for i = 1, 2, 3 and σ =↑ (↓)) are constant inside the sample.…”

Giant magnetoresistance of thin multilayers

“…Within the Boltzmann approach the value of this potential is usually taken as a constant, however, for very thin films the value of this potential depends on the thickness of the sample as it was reported in Ref. [3]. In the case of ultrathin films, the conduction electron transport behavior is influenced by the thickness of a sample (not only the thickness of spacer but also the thickness of ferromagnetic layer).…”

“…In Ref. [3] we discuss the influence of the sample thickness on some electronic properties like the Fermi energy, distribution of electrons and their spin polarisation. We justify some parameters introduced to the model potential whose values for spacer and ferromagnetic metals depend on the layer thickness.…”