Efficient Spin Injector Scheme Based on Heusler Materials

We present a rational design scheme intended to provide stable high spin polarization at the interfaces of the magnetoresistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principles calculations verify that the interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediately between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations.

Figure 1

(a) Crystal structures of the typical candidate materials: the half-metallic ferromagnet ${\mathrm{Co}}_2\mathrm{MnAl}$ and the nonmagnetic semiconductor CoMnVAl. (b) Their calculated bulk band structures. In case of ${\mathrm{Co}}_2\mathrm{MnAl}$ the bands of the gapped minority-spin channel are made thicker. The Fermi level is marked by the dashed line. (c) Structure of the supercell. Subsections marked as HM or SC represent the complete Heusler blocks, each containing four atomic layers.

Figure 2

Spin-resolved DOS (positive values correspond to majority-spin negative–to minority-spin channel) of the HM/SC supercells ($\mathrm{HM}={\mathrm{Co}}_2\mathrm{MnAl}$, $\mathrm{SC}=\mathrm{CoMnVAl}$) with $\mathrm{Co}\mathrm{\text{−}}\mathrm{Co}/\mathrm{V}\mathrm{\text{−}}\mathrm{Al}$, $\mathrm{Mn}\mathrm{\text{−}}\mathrm{Al}/\mathrm{Co}\mathrm{\text{−}}\mathrm{Mn}$ (a) and $\mathrm{Co}\mathrm{\text{−}}\mathrm{Co}/\mathrm{Mn}\mathrm{\text{−}}\mathrm{Co}$, $\mathrm{Mn}\mathrm{\text{−}}\mathrm{Al}/\mathrm{Al}\mathrm{\text{−}}\mathrm{V}$ (b) interface pairs. The gray shaded area corresponds to the minimal size of the supercell $(\mathrm{HM}{)}_1/(\mathrm{SC}{)}_1$ (scaled up by factor 4), and the thick blue curve corresponds to the largest $(\mathrm{HM}{)}_4/(\mathrm{SC}{)}_4$ supercell.

Figure 3

The black solid line represents the layer-resolved DOS at the Fermi energy with positive values referring to the majority-spin, negative–to the minority-spin channels (a, b, e, f) and the magnetic moments (c, d, g, h) calculated for HM/SC supercells ($\mathrm{HM}={\mathrm{Co}}_2\mathrm{MnAl}$, $\mathrm{SC}=\mathrm{CoMnVAl}$). Pale gray bars show the corresponding values calculated for the bulk HM and SC materials. Darker (colored) bars mark the atom-projected contributions within the first nearest and next-nearest interface layers (each layer contains two atoms). Vertical red dashed lines mark the interface borders.