First-principles prediction of spin-density-reflection symmetry driven magnetic transition of CsCl-type FeSe

Based on results of density functional theory (DFT) calculations with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), we propose a new magnetic material, CsCl-type FeSe. The calculations reveal the existence of ferromagnetic (FM) and antiferromagnetic (AFM) states over a wide range of lattice constants. At 3.12 in the GGA, the equilibrium state is found to be AFM with a local Fe magnetic moment of ±2.69μB. A metastable FM state with Fe and Se local magnetic moments of 2.00 and -0.032μB, respectively, lies 171.7 meV above the AFM state. Its equilibrium lattice constant is ∼2% smaller than that of the AFM state, implying that when the system undergoes a phase transition from the AFM state to the FM one, the transition is accompanied by volume contraction. Such an AFMFM transition is attributed to spin-density z-reflection symmetry; the symmetry driven AFMFM transition is not altered by spinorbit coupling. The relative stability of different magnetic phases is discussed in terms of the local density of states. We find that CsCl-type FeSe is mechanically stable, but the magnetic states are expected to be brittle.