Spin-polarized tunneling spectroscopy of fully epitaxial magnetic tunnel junctions usingCo2FeAl0.5Si0.5Heusler alloy electrodes

Abstract

Spin-dependent tunneling spectroscopy has been studied in fully epitaxial magnetic tunnel junctions with full-Heusler ${\text{Co}}_{2}{\text{FeAl}}_{0.5}{\text{Si}}_{0.5}$ (CFAS) alloys. We fabricated CFAS/MgO/CFAS structures with $L{2}_{1}$- and $B2$-ordered CFAS layers and measured the bias voltage dependence of differential conductance $G$. We found for $L{2}_{1}\text{-CFAS}/\text{MgO}/L{2}_{1}\text{-CFAS}$ structure symmetrical conductance curves with respect to polarity of the bias voltage for parallel (P) and antiparallel (AP) magnetization configurations and two characteristic crossovers in $G$ between P and AP accompanied with a flat feature within $\ifmmode\pm\else\textpm\fi{}0.6\text{ }\text{V}$ in $G$ (P). On the other hand, only one crossover was observed at a negative-bias voltage for $L{2}_{1}\text{-CFAS}/\text{MgO}/B2\text{-CFAS}$ structure. The direct tunneling that reflects the specific spin-dependent density of states of the half-metallic $L{2}_{1}\text{-CFAS}$ is proposed as a possible transport mechanism leading to the notable crossovers.