Spin-polarized tunneling through randomly transparent magnetic junctions: Reentrant magnetoresistance approaching the Jullière limit

Abstract

Electron conductance in planar magnetic tunnel junctions with long-range barrier disorder is studied within Glauber-eikonal approximation enabling exact disorder ensemble averaging by means of the HoltsmarkMarkov method. This allows us to address a hitherto unexplored regime of the tunneling magnetoresistance effect characterized by the crossover from k ʈ conserving to random tunneling ͑k ʈ is the in-plane wave vector͒ as a function of the defect concentration. We demonstrate that such a crossover results in a reentrant magnetoresistance: It goes through a pronounced minimum before reaching disorder-and geometry-independent Jullière's value at high defect concentrations.

Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions

“…At the same time, the Curie temperature of the ferromagnets corresponds to the voltage of order of 100 mV . The relation (36) between the spin-polarization of the current and the peak intensities for the parallel and antiparalell configurations is also consistent with experimental data [9,10].…”

“…Among various studies of the TMR effect a large body of work has aimed at developing theoretical approaches to spin-dependent tunneling in the single-particle approximation [15,16,17,18,19,20], including many-body spindependent phenomena [21,22,23,24,25,26,27,28,29,30,31] and effects of disorder [32,33,34,35,36].…”

Tunneling magnetoresistance in ferromagnetic planar hetero-nanojunctions

“…Our quasiclassical theory of TMR in planar junctions gives rise to high TMR $\simeq 250\%$ (in some cases $\simeq 500\%$ ) at small applied voltages, utilizing typical parameters (usually cited in the literature) such as spin polarizations of conduction bands, $\delta _{\rm L} = 0.38$ , $\delta _{\rm R} = 0.47$ , and MgO barrier height $V_{\rm B} \simeq 2.9$ eV. Comparable magnitudes of TMR could be obtained with a little bit higher conduction band polarizations in combination with the disorder effect at metal/insulator interfaces 24 or within the barrier material as well 25.…”