Large magnetoresistance in a manganite spin tunnel junction usingLaMnO3as the insulating barrier

Abstract

A spin-tunnel-junction based on manganites, with La1 xSrxMnO3 (LSMO) as ferromagnetic metallic electrodes and the undoped parent compound LaMnO3 (LMO) as insulating barrier, is here theoretically discussed using double exchange model Hamiltonians and numerical techniques. For an even number of LMO layers, the ground state is shown to have anti-parallel LSMO magnetic moments. This highly resistive, but fragile, state is easily destabilized by small magnetic fields, which orient the LSMO moments in the direction of the field. The magnetoresistance associated with this transition is very large, according to Monte Carlo and Density Matrix Renormalization Group studies. The influence of temperature, the case of an odd number of LMO layers, and the differences between LMO and SrTiO3 as barriers are also addressed. General trends are discussed. The study of strongly correlated electronic systems (SCES) continues attracting the attention of the Condensed Matter community. These materials present complex phase diagrams that illustrates the competition which exists among phases with very different physical properties, such as d-wave superconductivity, antiferroand ferro-magnetic order, charge- and orbital-order, multiferroic behavior, and several others. Moreover, this complexity and phase competition lead to self-organized nano-scale inhomogeneities which are believed to generate giant responses, as in the famous colossal magnetoresistance (CMR) effect of the Mn-oxides known as manganites. 1