Lattice collapse and quenching of magnetism in CaFe2As2 under pressure: A single crystal neutron and x-ray diffraction investigation

TL;DR

This study uses neutron and x-ray diffraction to map phase transitions in CaFe2As2 under pressure, revealing structural changes and the suppression of magnetism without additional phases or magnetic order in the collapsed tetragonal phase.

Contribution

It provides detailed experimental phase diagrams and insights into the magnetic and structural behavior of CaFe2As2 under pressure, including the absence of magnetic order in the cT phase.

Findings

Identification of phase boundaries between T, O, and cT phases.

No magnetic order detected in the cT phase.

Band calculations show reduced Fe 3d states at Fermi level.

Abstract

Single crystal neutron and high-energy x-ray diffraction have identified the phase lines corresponding to transitions between the ambient-pressure tetragonal (T), the antiferromagnetic orthorhombic (O) and the non-magnetic collapsed tetragonal (cT) phases of CaFe2As2. We find no evidence of additional structures for pressures up to 2.5 GPa (at 300 K). Both the T-cT and O-cT transitions exhibit significant hysteresis effects and we demonstrate that coexistence of the O and cT phases can occur if a non-hydrostatic component of pressure is present. Measurements of the magnetic diffraction peaks show no change in the magnetic structure or ordered moment as a function of pressure in the O phase and we find no evidence of magnetic ordering in the cT phase. Band structure calculations show that the transition results in a strong decrease of the iron 3d density of states at the Fermi energy, consistent with a loss of the magnetic moment.