Low-temperature magnetic ordering in SrEr$_2$O$_4$

TL;DR

This study investigates the low-temperature magnetic ordering in SrEr₂O₄ using neutron diffraction, specific heat, and magnetisation measurements, revealing anisotropic magnetic behavior, antiferromagnetic order below 0.75 K, and complex magnetic structure.

Contribution

First detailed characterization of magnetic structure and anisotropy in SrEr₂O₄ at low temperatures using multiple experimental techniques.

Findings

Antiferromagnetic order develops below 0.75 K.

Magnetic moments are aligned along the c axis.

Only one Er site has a significant ordered moment.

Abstract

SrEr$_2$O$_4$ has been characterised by low-temperature powder neutron diffraction, as well as single crystal specific heat and magnetisation measurements. Magnetisation measurements show that the magnetic system is highly anisotropic at temperature above ordering. A magnetic field of 280 kOe applied at $T=1.6$ K does not overcome the anisotropic magnetisation and fails to fully saturate the system. Long range antiferromagnetic ordering develops below $T_N=0.75$ K, identified by magnetic Bragg reflections with propagation vector ${\bf k}=0$ and a lambda anomaly in the specific heat. The magnetic structure consists of ferromagnetic chains running along the \textit{c} axis, two adjacent chains being stacked antiferromagnetically. The moments point along the \textit{c} direction, but only one of the two crystallographically in-equivalent Er sites has a sizeable ordered magnetic moment, 4.5 $\rm \mu_B$ at 0.55 K. The magnetic properties of SrEr$_2$O$_4$ are discussed in terms of the interplay between the low-dimensionality, competing exchange interactions, dipolar interactions and low lying crystal field levels.