Magnetic two-dimensional electron liquid at the surface of Heusler semiconductors

Conducting and magnetic properties of a material often change in some confined geometries. However, a situation where a nonmagnetic semiconductor becomes both metallic and magnetic at the surface is quite rare, or maybe even unique. In this Rapid Communication, we employ first-principles electronic structure theory to predict that such a peculiar magnetic state emerges in a family of quaternary Heusler compounds. We investigate magnetic and electronic properties of CoCrTiP, FeMnTiP, and CoMnVAl. For the latter material, we also analyze the structural stability of various surface terminations. For the ideal CoMn termination we calculate the magnetic exchange interactions and use them for parametrizing an effective spin Hamiltonian. According to our results, magnetism in this material should persist at temperatures at least as high as 160 K.