Structural, electronic, magnetic and spin dependent transport properties of Fe/CaS/Fe (001) heterostructures

Abstract

Structural, electronic, and magnetic properties of Fe/CaS (001) interfaces and Fe/CaS/Fe (001) heterostructures have been studied by means of a self-consistent Green's function technique for surface and interfaces implemented within the tight-binding linear muffin-tin orbital formalism. Spin dependent transport properties of the Fe/CaS/Fe (001) tunnel junctions with thin and intermediate barriers, in the current-perpendicular-to-plane geometry, have been determined by means of Kubo-Landauer approach implemented within the tight-binding linear muffin-tin orbital formalism. A small charge rearrangement is evidenced at the Fe/CaS (001) interfaces. The iron interfacial magnetic moments are enhanced over the bulk value. A small exchange coupling with the sign depending on the Fe/CaS (001) interface geometric structure and the strength decaying exponentially with the barrier is evidenced. Interfacial charge transfer, interface iron magnetic moments, and tunneling currents are sensitive to the interfacial structure. Interface resonant states have a decisive role in the tunneling process and the main contribution to the current in the ferromagnetic state of the junction is given by the minority-spin electrons.

Oscillatory exchange coupling and strong direct tunnelling with AgCl based heterojunctions

“…Therefore IC 2 interfacial geometry appears to be favoured. This result is in contrast with the behaviour observed for either Fe/ NaCl (0 0 1) [16] or Fe/CaS (0 0 1) [17] heterointerfaces but agree with the interfacial geometry predicted for Cu/LiCl (0 0 1) heterointerfaces [55]. Additionally, the energy differences between Fe/ AgCl/Fe (0 0 1) heterostructures with IC 1 and IC 2 interfacial geometries are greater than those determined for Fe/NaCl/Fe (0 0 1) and Fe/CaS/Fe (0 0 1) systems.…”

“…Their contributions to the majority-spin conductance depend on the interfacial structure, D 1 states being rather decoupled for the interfacial configuration with Fe atoms located above the hollow sites between Ca and S atoms. IRSs were found to play a major role on the spin-polarized transport for both NaCl and CaS based tunnel junctions and depending on Fe/NaCl(CaS) (0 0 1) interfacial geometry, extremely large TMR values have been predicted [16,17]. D 1 band symmetry selection of NaCl barrier and the possibility to obtain large TMR values by combining the direct and resonant tunnelling have been confirmed by the recent study of FePt/NaCl/FePt tunnel junctions [36].…”

“…Additionally, the energy differences between Fe/ AgCl/Fe (0 0 1) heterostructures with IC 1 and IC 2 interfacial geometries are greater than those determined for Fe/NaCl/Fe (0 0 1) and Fe/CaS/Fe (0 0 1) systems. Hence we expect to have rather stronger interactions at Fe/AgCl (0 0 1) heterointerfaces than those at Fe/ NaCl (0 0 1) [16] and Fe/CaS (0 0 1) [17] ones. A similar behaviour was observed for Ag-AgCl cluster composites where the silver clusters shown strong interactions with AgCl surface [56].…”

“…In addition, the majority-spin FM conductance is sensitive to the interfacial geometry. In contrast with the direct band gap MgO and NaCl based junctions, Fe/CaS/Fe (0 0 1) heterostructures [17] have an interlayer with indirect C-X band gap. The main contribution to the majority-spin FM conductances results from D 1 and D 5 states in agreement with the complex band structure of CaS barrier.…”

“…First-principles studies performed for Fe/ZnSe/Fe heterostructures have shown that the exchange coupling between Fe electrodes across ZnSe barriers is interface termination sensitive and oscillate between FM and AFM states when increasing the barrier thickness [14]. Recent first-principles investigations of Fe/NaCl/Fe (0 0 1) [15,16] and Fe/ CaS/Fe (0 0 1) [17] heterostructures have revealed the presence of small exchange couplings with exponential decays as function of the barriers thickness, in qualitative agreement with the spin-current model of Slonczewski [18] and quantum-interference model of Bruno [19]. Although the strength and the sign of the couplings relate rather with the properties of the electrode/barrier electronic http://dx.doi.org/10.1016/j.jallcom.2015.01.023 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.…”