Magnetic phase diagram in the Co-rich side of LnCo1-xFexAsO (Ln=La, Sm) system

TL;DR

This study maps the magnetic phase diagram of LnCo1-xFexAsO compounds, revealing how Fe doping and rare earth elements influence magnetic transitions and interactions between 3d and 4f electrons.

Contribution

It provides the first detailed magnetic phase diagram for the Co-rich side of LnCo1-xFexAsO, highlighting the effects of Fe doping and rare earth substitution on magnetic order.

Findings

Fe doping suppresses ferromagnetic and antiferromagnetic transitions.

Sm 4f-electron magnetism remains robust against Fe doping.

The magnetic phase diagram is rich and complex, influenced by 3d and 4f electron interactions.

Abstract

The magnetic phase diagram has been mapped out via the measurements of electronic resistivity, magnetization and specific heat in the cobalt-based layered LnCo1-xFexAsO (Ln=La, Sm) compounds. The ferromagnetic (FM) transition at 63 K for LaCoAsO is rapidly suppressed upon Fe doping, and ultimately disappears around x=0.3 in the LaCo1-xFexAsO system. When La is replaced by magnetic rare earth element Sm, the 3d electrons first undergo a FM transition at Tc = 75 K, followed by an antiferromagnetic (AFM) transition at a lower temperature TN1 = 45 K. With partial Fe doping on the Co site, both FM (Tc) and AFM (TN1) transition temperatures are significantly suppressed, and finally approach zero kelvin at x = 0.3 and 0.2, respectively. Meanwhile, a third magnetic transition at TN2 = 5.6 K for SmCoAsO, associated with the AFM order of the Sm3+ 4f-oments, is uncovered and TN2 is found to be almost robust against the small Fe-doping. These results suggest that the 4f electrons of Sm3+ have an important effect on the magnetic behavior of 3d electrons in the 1111 type Co-based LnCo1-xFexAsO systems. In contrast, the magnetism of the f-electrons is relatively unaffected by the variation of the 3d electrons. The rich magnetic phase diagram in the Co-rich side of the LnCo1-xFexAsO system, therefore, is established.