Magnetotransport and Structural Properties of Mn$_{2}$CoAl Thin Film Spin Gapless Semiconductor

Spin gapless semiconductors (SGS) are predicted to have a density of states displaying both half-metallic and zero-gap semiconducting properties. They are being investigated for spintronic devices due to their unique magnetic and electrical properties. Calculations predict several SGS compounds\footnote{S. Skaftouros, K. Ozdogan, E. Sasioglu, and I. Galanakis, App. Phys. Lett. 102, 022402 (2013).}$^,$\footnote{S. Ouardi, G. Fecher, and C. Felser, and J. Kubler, Phys. Rev. Lett. 110, 100401 (2013).} including Mn$_{2}$CoAl, Ti$_{2}$CoSi, V$_{3}$Al, and Ti$_{2}$MnAl. Mn$_{2}$CoAl thin films were grown by MBE on GaAs (100) substrates at 200 $^{\circ}$C.\footnote{M.E. Jamer, B.A. Assaf, T. Devakul and D. Heiman, Appl. Phys. Lett. 103, 142403 (2013).} The as-grown thin films were epitaxial with the substrate, which resulted in a tetragonal distortion. Annealing studies showed that the films lose their epitaxial registration and approach an aligned cubic structure for 325 $^{\circ}$C with a$=$c$=$5.80 {\AA}. The resistivity shows a thermally-activated semiconducting-like negative slope at higher temperatures. The Hall resistivity scales with $\rho _{xx}^{2}$ for all temperatures and magnetic fields, expected for a topological intrinsic anomalous Hall effect computed from the Berry phase curvature. The connection of electrical and spin-gapless properties is discussed.