# Realization of the Axial Next-Nearest-Neighbor Ising model in U$_3$Al$_2$Ge$_3$

## TL;DR

This study combines neutron scattering and theoretical modeling to demonstrate that U$_3$Al$_2$Ge$_3$ exhibits phase transitions consistent with the three-dimensional Axial Next-Nearest-Neighbor Ising model, highlighting its role in frustrated magnetism.

## Contribution

It provides experimental evidence and theoretical analysis showing U$_3$Al$_2$Ge$_3$ as a realization of the Axial Next-Nearest-Neighbor Ising model.

## Key findings

- Observation of a second-order phase transition at 63 K.
- Detection of a first-order transition at 48 K.
- Significant change in the magnetic ordering wave-vector with temperature.

## Abstract

Here we report small-angle neutron scattering (SANS) measurements and theoretical modeling of U$_3$Al$_2$Ge$_3$. Analysis of the SANS data reveals a phase transition to sinusoidally modulated magnetic order, at $T_{\mathrm{N}}=63$~K to be second order, and a first order phase transition to ferromagnetic order at $T_{\mathrm{c}}=48$~K. Within the sinusoidally modulated magnetic phase ($T_{\mathrm{c}} < T < T_{\mathrm{N}}$), we uncover a dramatic change, by a factor of three, in the ordering wave-vector as a function of temperature. These observations all indicate that U$_3$Al$_2$Ge$_3$ is a close realization of the three-dimensional Axial Next-Nearest-Neighbor Ising model, a prototypical framework for describing commensurate to incommensurate phase transitions in frustrated magnets.