Structural and magnetic transition in CeFeAsO: separated or connected?

TL;DR

This study presents high-quality CeFeAsO single crystals revealing that the separation between structural and magnetic transitions is not intrinsic, and suggests a strong coupling between magnetic and structural properties similar to other iron-based superconductors.

Contribution

The paper reports improved crystal growth techniques and detailed measurements showing the non-intrinsic nature of transition separation and coupling in CeFeAsO.

Findings

High-quality CeFeAsO crystals with sharper phase transition anomalies

The transition separation decreases with sample quality, indicating non-intrinsic nature

Magnetic and structural coupling similar to AFe2As2 compounds

Abstract

Using an adapted Sn-flux growth technique we obtained comparatively large CeFeAsO single crystals of better quality than previously reported polycrystals or single crystals, as evidenced by much sharper anomalies at the structural and magnetic phase transitions as well as a much higher residual resistivity ratio of 12. In the magnetically ordered phase we observe a very pronounced metallic behavior of the in-plane resistivity, which excludes a Mott insulator regime at low temperature. The separation Delta_T = T_0 - T_N between structural and magnetic ordering temperatures decreases with increasing sample quality, from 18 K in the initial reports to 6 K in the present single crystals, demonstrating that this separation is not an intrinsic property of the RFeAsO systems. Our results indicate that the coupling between magnetic ordering and structural distortion is very similar in AFe2As2 and RFeAsO type of compounds, much more similar than previously thought. The implications of our experimental results give arguments both in favor and against the nematic phase model.