# Time-of-flight elastic and inelastic neutron scattering studies on the localized $4d$ electron layered perovskite La$_5$Mo$_4$O$_{16}$

## TL;DR

This study investigates the magnetic structure and excitations of La$_5$Mo$_4$O$_{16}$ using neutron scattering, revealing ferrimagnetic order, magnetic anisotropy, and explaining magnetic properties with a detailed Hamiltonian.

## Contribution

The paper provides the first detailed neutron scattering analysis of La$_5$Mo$_4$O$_{16}$'s magnetic structure and excitations, highlighting the role of spin-orbit interaction and anisotropy.

## Key findings

- Ferrimagnetic magnetic structure with antiferromagnetic stacking along c-axis.
- Strong easy-axis magnetic anisotropy due to spin-orbit interaction.
- Model Hamiltonian explains neutron scattering data and magnetic properties.

## Abstract

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2)\mu_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and $1.07(3)\mu_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.