Realization of the Axial Next-Nearest-Neighbor Ising model in U3Al2Ge3

Abstract

Here we report small-angle neutron scattering (SANS) measurements and theoretical modeling of U3Al2Ge3. Analysis of the SANS data reveals a phase transition to sinusoidally modulated magnetic order, at TN = 63 K to be second order, and a Lifshitz phase transition to ferromagnetic order at Tc = 48 K. Within the sinusoidally modulated magnetic phase (Tc < T < TN), we uncover a dramatic change in the ordering wave-vector as a function of temperature. These observations all indicate that U3Al2Ge3 is a close realization of the threedimensional Axial Next-Nearest-Neighbor Ising model, a prototypical framework for describing commensurate to incommensurate phase transitions in frustrated magnets.