Spin-orbit coupling effect by minority interface resonance states in single-crystal magnetic tunnel junctions

Abstract

Spin-orbit coupling (SOC) related to the minority interface resonance states (IRSs) of Fe(001) has been evidenced in full-epitaxial Fe(001)/MgO/Fe magnetic tunnel junctions (MTJs) from magnetotransport experiments correlated to theoretical ab initio calculations. We show that the SOC effect strongly depends on the symmetry composition of the IRS, which has been skillfully engineered via the interfacial chemical structure in the Fe(001)/MgO stack. The SOC scattering is enhanced between the majority 1 and minority 5 band near the Fermi level when presenting a 5 symmetry dominant IRS at the Fe/MgO interface. Our results validate the interplay between SOC and IRSs, which gives further understanding of the mechanisms responsible for the tunneling anisotropic magnetoresistance and the large perpendicular magnetic anisotropy at the Fe/MgO interface.

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

“…From a theoretical point of view, the difficulty is then to quantify the effect of these * christine.bellouard@univ-lorraine.fr † coriolan.tiusan@phys.utcluj.ro defects on the electronic band structure. In the case of carbon contamination at the interface, good agreements have been observed between experimental features and ab initio calculation [18]. Historically, carbon contamination of bottom Fe(001)/MgO interface in MTJs allowed the observation of the signature of the Fe surface state in magnetotransport measurements with MTJs in the asymptotic regime [17].…”

“…In Fig. 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].…”

“…4(a)] measured for the reference junctions (flat Fe buffer) are about 100%. This TMR value is well below the 180% usually obtained at room temperature in single-crystalline Fe/MgO/Fe MTJs [18]. Indeed, we recall that the hard electrode of the MTJ has not been annealed (as for high TMR ratio junctions) to avoid any structural rearrangements at the bottom interface.…”

“…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]. It is located in the minority band and arrives in the¯ point just above the Fermi level.…”

“…It has been shown that volume defects in the barrier as misfit dislocations are detrimental for TMR [13][14][15][16]. Surprisingly, controlled contamination of the interface with carbon [17,18], or oxygen has been found to have small impact on TMR values (at zero voltage) [19,20]. From a theoretical point of view, the difficulty is then to quantify the effect of these * christine.bellouard@univ-lorraine.fr † coriolan.tiusan@phys.utcluj.ro defects on the electronic band structure.…”