Crystal structure and high-field magnetism of La2CuO4

TL;DR

This study reveals a subtle monoclinic distortion in La2CuO4, details its magnetic spin reorientation under high magnetic fields, and confirms a spin-flop transition with new quantitative insights.

Contribution

The paper uncovers a previously unreported monoclinic distortion in La2CuO4 and demonstrates magnetic spin reorientation driven by in-plane magnetic fields.

Findings

Detection of monoclinic distortion in La2CuO4

Continuous reorientation of copper spins under magnetic field

Observation of a spin-flop transition at 11.5 T

Abstract

Neutron diffraction was used to determine the crystal structure and magnetic ordering pattern of a La2CuO4 single crystal, with and without applied magnetic field. A previously unreported, subtle monoclinic distortion of the crystal structure away from the orthorhombic space group Bmab was detected. The distortion is also present in lightly Sr-doped crystals. A refinement of the crystal structure shows that the deviation from orthorhombic symmetry is predominantly determined by displacements of the apical oxygen atoms. An in-plane magnetic field is observed to drive a continuous reorientation of the copper spins from the orthorhombic b-axis to the c-axis, directly confirming predictions based on prior magnetoresistance and Raman scattering experiments. A spin-flop transition induced by a c-axis oriented field previously reported for non-stoichiometric La2CuO4 is also observed, but the transition field (11.5 T) is significantly larger than that in the previous work.