Interfacial Resonance State Probed by Spin-Polarized Tunneling in EpitaxialFe/MgO/FeTunnel Junctions

Abstract

The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe/MgO/Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe/MgO interface. The voltage variation of the conductance points out the signature of an interfacial resonance state located in the minority band of Fe(001). When coupled to a metallic bulk state, this spin-polarized interfacial state enhances the band matching at the interface and therefore increases strongly the conductivity in the antiparallel magnetization configuration. Consequently, the tunnel magnetoresistance is found to be positive below 0.2 V and negative above. On the other hand, when the interfacial state is either destroyed by roughness-related disorder or not coupled to the bulk, the magnetoresistance is almost independent on the bias voltage.

Enhanced magnetoresistance by monoatomic roughness in epitaxial Fe/MgO/Fe tunnel junctions

“…4(f), three peaks are observed: Two symmetric ones are located at ±0.037 V attributed to magnon excitations [18]; the stronger one located only at −0.14 V reveals the asymmetry of the interfacial electronic structure. It has been previously attributed to the interfacial resonance state surviving in MTJ stacks with a high-quality bottom interface [31]. Previous studies have shown that it can be tuned by interface quality [21] or chemical doping [18].…”

High inverted tunneling magnetoresistance in MgO-based magnetic tunnel junctions

“…7 Moreover, an interfacial resonance state located in the minority band of Fe ͑001͒, which has been probed by spin-polarized tunneling in epitaxial Fe/ MgO / Fe MTJs, causes the TMR to change sign from positive to negative above a critical voltage. 8 Here we report the observation of a high inverted magnetoresistance when the free layer in MgO-based MTJs switches at zero bias. A switch in the sign of the resistance change near zero applied field occurs as a function of the thickness of the pinned CoFeB layer next to the MgO barrier in an MTJ stack with a synthetic antiferromagnet.…”

Voltage-controlled inversion of tunnel magnetoresistance in epitaxial nickel/graphene/MgO/cobalt junctions

“…Inversions of TMR with varying bias voltage have already been reported for epitaxial spinvalves [12,13,14]. They most often occur due to the voltage-induced opening/closing of conduction channels associated with spin-polarized electronic bands or surface states close to the Fermi level.…”

“…Assuming implicitly that Ni was (111)-oriented, the authors related the negative TMR to the theoretical prediction made by Karpan et al [6,7] of a negative tunneling spin polarization at the K point of the GPFE Brillouin zone. However, the voltage bias dependence of the TMR, which is critically important to understand the interfacial effects [12,13,14], has not been studied. Such bias dependence investigation is of primary importance in view of the recent first principle non-equilibrium transport calculations, which predict a non-trivial dependence of the spin polarization with varying applied voltage at Gr|Co(111) and Gr|Ni(111) interfaces [15].…”