First-Principles study of vibrational and non-collinear magnetic properties of the perovskite to post-perovskite pressure transition of NaMnF3

摘要

We performed a first-principles study of the structural, vibrational,electronic and magnetic properties of NaMnF3 under applied isotropic pressure.We found that NaMnF3 undergoes a reconstructive phase transition at 8 GPa fromthe Pnma distorted perovskite structure toward the Cmcm post-perovskitestructure. This is confirmed by a sudden change of the Mn-F-Mn bondings wherethe crystal goes from corner shared octahedra in the Pnma phase to edge sharedoctahedra in the Cmcm phase. The magnetic ordering also changes from a G-typeantiferromagnetic ordering in the Pnma phase to a C-type antiferromagneticordering in the Cmcm phase. Interestingly, we found that the high-spind-orbital filling is kept at the phase transition which has never been observedin the known magnetic post-perovskite structures. We also found a highlynon-collinear magnetic ordering in the Cmcm post-perovskite phase that drives alarge ferromagnetic canting of the spins. We discuss the validity of theseresults with respect to the U and J parameter of the GGA+U exchange correlationfunctional used in our study and conclude that large spin canting is apromising property of the post-perovskite fluoride compounds.