Electronic and Magnetic Properties of TMPO$_{\mathrm{4}}$ (TM$=$Fe, Mn, Cr)

Advances in experiment and theory continue to increase our understanding of macroscopic and atomistic structure/property relationships in materials. However, solving the property to structure problem, and hence rational materials design remains challenging at present. Here we report on the use of a few simple rules to design a structural template for a new class of half-metals. In the proposed structure tetrahedral TMO$_{\mathrm{4}}$ (TM$=$Fe, Mn, Cr) groups share corners with intermittent PO$_{\mathrm{4}}$ groups to form a 3d periodic bond topology. All computations are based on spin-polarized Density-Functional-Theory (DFT) computations at the GGA-PBE level using all-electron like PAW interaction potentials. FePO$_{\mathrm{4}}$ is antiferromagnetic consistent with experimental observations. In contrast, the DFT results for TM$=$ Mn and Cr predict half-metallicity: a spin-gap in the minority spin channel and integer magnetic moments of 3 $\mu_{\mathrm{B}}$/fu and 4 $\mu _{\mathrm{B}}$/fu for the Cr and Mn compound, respectively. Furthermore, in both compounds the half-metallic state is energetically more favorable as compared to the competing antiferromagnetic state. We will also discuss our DFT$+$U results that allow assessing the reliability of the DFT predictions that MnPO$_{\mathrm{4}}$ and CrPO$_{\mathrm{4}}$ are half-metals.