Influence ofs−dinterfacial scattering on the magnetoresistance of magnetic tunnel junctions

Abstract

We propose the two-band s-d model to describe theoretically a diffuse regime of the spin-dependent electron transport in magnetic tunnel junctions (MTJ's) of the form F/O/F where F's are 3d transition metal ferromagnetic layers and O is the insulating spacer. We aim to explain the strong interface sensitivity of the tunneling properties of MTJ's and investigate the influence of electron scattering at the nonideal interfaces on the degradation of the TMR magnitude. The generalized Kubo formalism and the Green's functions method were used to calculate the conductance of the system. The vertex corrections to the conductivity were found with the use of "ladder" approximation combined with the coherent-potential approximation (CPA) that allowed to consider the case of strong electron scattering. It is shown that the Ward identity is satisfied in the framework of this approximation that provides the necessary condition for a conservation of a tunneling current. Based on the known results of ab-initio calculations of the TMR for ballistic junctions, we assume that exchange split quasi-free s-like electrons with the density of states being greater for the majority spin sub-band give the main contribution to the TMR effect. We show that, due to interfacial inter-band scattering, the TMR can be substantially reduced even down to zero value. This is related to the fact that delocalized quasi-free electrons can scatter into the strongly localized d sub-band with the density of states at the Fermi energy being larger for minority spins compared to majority spins. It is also shown that spin-flip electron scattering on the surface magnons within the interface leads to a further decrease of the TMR at finite temperature.

Temperature and bias-voltage dependent transport in magnetic tunnel junctions with low energy Ar-ion irradiated barriers

“…For example, the influence of the barrier termination on the atomic and electronic structure in Co/Al 2 O 3 /Co junctions is pointed out by Oleinik et al 14 The spin polarization can also be effected by the actual profile of the potential barrier, 15,16 the disorder in the barrier, 17 and the mechanism of bonding at the interface between the barrier and the electrode. 18 The degrading influence of nonideal interfaces on the TMR is discussed recently by Bagrets et al 19 If the TMR at 4.2 K and 300 K is compared for different scattering parameters ␥ ͑see Fig. 8 in Ref.…”

Optical and magneto-optical properties and magnetorefractive effect in metal-insulator CoFe–Al2O3 granular films

“…But recently Bagrets et al 18 calculated the tunneling magnetoresistance as a function of a scattering parameter ␥ in the case of elastic scattering on the interfaces only. It is evident from Eq.…”

Barrier thickness dependence of the magnetoresistance in TaOx magnetic tunnel junctions

“…This relative hot-electron efficiency decrease can be attributed to the structural changes near the barrier interfaces with increasing Ta thickness, for example caused by s-d interfacial scattering. 13 Similarly, these structural changes may cause the observed decrease of the MR ratio with increasing Ta thickness.…”

“…11 Alternatively it might be of extrinsic origin, related to a lower structural quality of the tunnel barrier, e.g., caused by defects or impurities. 12,13 It is difficult to extract information on the tunneling spin polarization itself in these heavy metal oxide barriers, as shown by Kant et al 14 Instead, we will focus on the structural origin of the electron transport characteristics. In this paper we present results from a systematic study of the dependence of the MR ratio on the thickness of TaO x barrier layers.…”