Microscopic phase diagram of LaFeAsO single crystals under pressure

TL;DR

This study maps the microscopic magnetic phase diagram of LaFeAsO single crystals under pressure, revealing a continuous suppression of magnetic order up to 7.5 GPa, contrasting with polycrystalline behavior, and aligning with theoretical predictions.

Contribution

It provides the first detailed microscopic phase diagram of LaFeAsO single crystals under pressure, highlighting differences from polycrystalline samples and confirming theoretical models.

Findings

Magnetic hyperfine field vanishes at ~7.5 GPa in single crystals.

Magnetic order persists up to higher pressures in polycrystals (~20 GPa).

Magnetic transition temperature decreases with increasing unit cell volume.

Abstract

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 $\sim$ 7.5 GPa which is in contrast to the behavior in polycrystalline samples where the magnetic order vanishes at $\sim$ 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.