Microscopic Phase Diagram Of Lafeaso Single Crystals Under Pressure

We investigated a LaFeAsO single crystal by means of synchrotron Mossbauer spectroscopy under pressure 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 similar to 7.5 GPa, which is in contrast to the behavior in polycrystalline samples where the magnetic order vanishes at similar to 20 GPa. The different behaviors 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 the magnetic phase-transition temperature as well as the low-temperature magnetic hyperfine field decrease with increasing unit-cell volume.