Magnetic structure and magnon dispersion in LaSrFeO$_4$

TL;DR

This study uses neutron scattering to analyze the magnetic structure and magnon dispersion in LaSrFeO$_4$, confirming known magnetic arrangements and providing detailed insights into exchange interactions and anisotropy gaps.

Contribution

The paper provides new neutron scattering data clarifying the magnetic structure and magnon dispersion in LaSrFeO$_4$, with precise measurements of exchange parameters and anisotropy gaps.

Findings

Magnetic moments lie in the tetragonal basal plane.

Magnon dispersion is explained by linear spin-wave theory with specific exchange parameters.

The dispersion exhibits a gapped out-of-plane anisotropy at 5.26 meV.

Abstract

We present elastic and inelastic neutron scattering data on LaSrFeO$_4$. We confirm the known magnetic structure with the magnetic moments lying in the tetragonal basal plane, but contrarily to previous reports our macroscopic and neutron diffraction data do not reveal any additional magnetic phase transition connected to a spin reorientation or to a redistribution of two irreducible presentations. Our inelastic neutron scattering data reveals the magnon dispersion along the main-symmetry directions [0 $\xi$ 0] and [$\xi$ -$\xi$ 0]. The dispersion can be explained within linear spin-wave theory yielding an antiferromagnetic nearest-neighbour interaction parameter $J_{1}=7.4(1)$ meV and a next-nearest neighbour interaction parameter $J_{2}=0.4(1)$ meV. The dispersion is gapped with the out-of-plane anisotropy gap found at $\Delta_{out}=5.26(2)$ meV, while evidence is present that the in-plane anisotropy gap lies at lower energies, where it cannot be determined due to limited instrument resolution.