Rare earth magnetism in CeFeAsO: A single crystal study

TL;DR

This study provides a detailed single-crystal analysis of CeFeAsO, revealing its magnetic anisotropy, phase transitions, and the nature of Ce magnetic ordering, challenging previous assumptions about the influence of Fe magnetic order on Ce ions.

Contribution

First high-quality single-crystal growth of CeFeAsO enabling anisotropic magnetic property studies, with insights into Ce magnetic order and crystal electric field effects.

Findings

High residual resistivity ratio indicating crystal quality

Large easy-plane magnetic anisotropy observed

Ce magnetic order occurs at T_N = 3.7 K, with reduced Zeeman splitting below 15 K

Abstract

Single crystals of CeFeAsO, large enough to study the anisotropy of the magnetic properties, were grown by an optimized Sn-flux technique. The high quality of our single crystals is apparent from the highest residual resistivity ratio, RRR = 12, reported among undoped RFeAsO compounds (R=rare earth) as well as sharp anomalies in resistivity, specific heat, C(T), and thermal expansion at the different phase transitions. The magnetic susceptibility chi(T) presents a large easy-plane anisotropy consistent with the lowest crystal electric field doublet having a dominant Gamma_6 character. Curie-Weiss like susceptibilities for magnetic field parallel and perpendicular to the crystallographic c-axis do not reveal an influence of a staggered field on the Ce site induced by magnetic ordering of the Fe. Furthermore, the standard signatures for antiferromagnetic order of Ce at T_N = 3.7 K observed in chi(T) and C(T) are incompatible with a Zeeman splitting Delta = 10 K of the CEF ground state doublet at low temperature due to the Fe-magnetic order as previously proposed. Our results can be reconciled with the earlier observation by assuming a comparatively stronger effect of the Ce-Ce exchange leading to a reduction of this Zeeman splitting below 15 K.