We investigated LaFeAsO single crystals by means of synchrotron M\"ossbauer spectroscopy under pressures up to 7.5 GPa and down to 13 K and provide a microscopic phase diagram. We found a continuous suppression of the magnetic hyperfine field with increasing pressure and it completely vanishes at ∼ 7.5 GPa which is in contrast to the behavior in polycrystalline samples where the magnetic order vanishes at ∼ 20 GPa. The different behavior of the polycrystalline samples might be due to As-vacancies. Our results are in qualitative agreement with density functional theory calculations where a reduction of the magnetic moment with increasing pressure was found. We found that among different samples at ambient pressure the magnetic phase transition temperature as well as the low-temperature magnetic hyperfine field decrease with increasing unit cell volume.
@article{arxiv.1808.06654,
title = {Microscopic phase diagram of LaFeAsO single crystals under pressure},
author = {Philipp Materne and Wenli Bi and Jiyong Zhao and Michael Y. Hu and Rhea Kappenberger and Sabine Wurmehl and Saicharan Aswartham and Bernd Büchner and E. Ercan Alp},
journal= {arXiv preprint arXiv:1808.06654},
year = {2018}
}