Stability of half-metallic antiferromagnet La2VMnO6, first-principles calculation study

The double perovskite La2VMnO6 with a Fm3¯m structure was predicted by Pickett et al. as a half-metal (HM) antiferromagnet (AFM) based on first principle calculations, while Androulakis et al.'s experimental result showed that La2VMnO6 also exhibits the same structure as a ferrimagnetic (FiM) state. For thoroughly understanding what happens in the double perovskite La2VMnO6 with a Fm3¯m structure, we first calculated the fixed cubic Fm3¯m structure before recalculating the structure through an optimization process. Our results show that La2VMnO6 is a FiM state when found in the fixed and volume-relaxed cubic Fm3¯m structure. However, after full relaxation, it becomes a HM-AFM and remains the same state even on-site Coulomb interactions (+U) are taken into consideration. This recalculation illustrates that the magnetic state of the Mn ion is sensitive to the crystal field of MnO6 octahedron, and is the main reason behind the transformation of the magnetic state of La2VMnO6 from a FiM to a AFM state after full relaxation. Because the difference of total energy ΔEFiM−AFM is small (merely about 57.1 meV/f.u.) and shows up as nearly the same space group in both FiM and AFM states La2VMnO6, we conclude that in which state it is mainly determined by the crystal field of the MnO6 octahedron, i.e. the distortion magnitude of the MnO6 octahedron, which is related to the process of synthesis. Although Androulakis et al.'s experimental result show that this is a Fm3¯m/FiM state, we think that it is still possible for a I4/mmm/AFM state to exists, i.e. a HM-AFM La2VMnO6.