Low moment ferrimagnetism in Mn$_3$Al as probed by Polarized Neutron Reflectometry

For future spintronic devices, it is paramount to limit stray magnetic interactions which can negatively impact spin injection. A new class of materials called half-metallic antiferromagnets or compensated ferrimagnets have been proposed to remedy this problem. In this work, Mn$_3$Al thin films have shown promising room temperature low-moment ferrimagnetic magnetic properties. Epitaxial Mn$_3$Al thin films (50 nm) were grown on desorbed GaAs(001) substrates via MBE at 200 $^o$C and annealed further to temperatures between 250 - 350 $^o$C. The D0$_3$ Heusler-type phase was determined by X-ray diffraction with texturing in the [311] direction. Density functional theory, performed using VASP, indicated that the crystallographic structure of Mn$_3$Al is able to form energetically with a low magnetic moment (0.017 $\mu_B$/f.u.) despite some epitaxial distortion. SQUID magnetometry confirmed the low magnetic moment and high Curie temperature (610 K) of the structure. Polarized Neutron Reflectometry was used to determine the effect of epitaxy on the magnetic moment of Mn$_3$Al, and analysis confirms a low magnetic moment (0.11 $\mu_B$/f.u.) for the samples annealed at temperatures between 200-300 $^o$C. This analysis further suggests that the relaxation of the Mn$_3$Al at the interface.