Incommensurate Magnetic Ordered Phase with Enhanced Low-Temperature Magnetic Specific Heat in SmAu$_3$Al$_7$

TL;DR

This study investigates the magnetic ordering in SmAu$_3$Al$_7$, revealing an incommensurate long-range magnetic order below 2.8 K and its relation to enhanced low-temperature specific heat.

Contribution

It provides the first detailed neutron and muon spin rotation analysis showing incommensurate magnetic order in SmAu$_3$Al$_7$ and clarifies its nature compared to previous hypotheses.

Findings

Magnetic Bragg peaks appear below 2.8 K with an incommensurate propagation vector.

Muon spin rotation detects spontaneous internal fields consistent with incommensurate order.

No anomalies at 0.9 K suggest the magnetic structure remains unchanged across this transition.

Abstract

Neutron scattering and muon spin rotation ($\mu$SR) measurements on single-crystal SmAu$_3$Al$_7$ reveal magnetically ordered states associated with successive transitions at $T_{\rm N}$ = 2.8 K and $T^*$ = 0.9 K. Magnetic Bragg peaks appear below $T_{\rm N}$ with an incommensurate (IC) propagation vector ${\bf q}$ = (0.30, 0, 1.33). $\mu$SR detects spontaneous internal fields below $T_{\rm N}$, and the spectral shape is consistent with the IC magnetic ordering. No anomalies are observed at $T^*$, indicating that the magnetic structure remains essentially unchanged below and above $T^*$. The magnetic order is revealed to be a spatially homogeneous long-range ordered state, rather than a partially disordered state proposed in earlier studies. The possible connection between the IC magnetic order and the enhanced low-temperature magnetic specific heat is discussed.