Tunneling spectroscopy of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>n</mml:mi></mml:math>-type ferromagnetic semiconductor (In,Fe)Sb using single-barrier heterostructures

We study tunneling anisotropic magnetoresistance in single-barrier tunnel junctions consisting of an $n$-type ferromagnetic semiconductor (In,Fe)Sb electrode, an (In,Al)Sb tunnel barrier, and an $n$-type InSb electrode. We measured the current-voltage ($I\text{\ensuremath{-}}V$) characteristics in the junctions and plotted the change in tunnel resistance $R$ or $\mathrm{d}I\text{/}\mathrm{d}V$ values when an external magnetic field $\mathbit{H}$ was rotated between out-of-plane and in-plane directions with respect to the crystalline axes of the (In,Fe)Sb thin films. We observe a sizeable decrease in the junction resistance when $\mathbit{H}$ is rotated from the perpendicular $[001]$ direction to the in-plane $[110]$ direction, whose origin is explained by considering $\mathbit{H}$ direction dependent $s\text{\ensuremath{-}}d$ scatterings and the $s$,p-d hybridized band picture of (In,Fe)Sb. Meanwhile, when $\mathbit{H}$ is rotated in the film plane, we observe a twofold anisotropic change in the $\mathrm{d}I\text{/}\mathrm{d}V$ with a maximum and a minimum when $\mathbit{H}$ is along the $[\overline{1}10]$ and $[110]$ crystal axes, respectively. This result reflects in-plane twofold anisotropy in the density of states of the impurity band of (In,Fe)Sb, whose origin is attributed to a possible preferential distribution of Fe atoms along the $[\overline{1}10]$ direction.