Non-collinear ferromagnetism in the Kondo lattice Ce$_5$CoGe$_2$

TL;DR

This study uncovers a noncollinear ferromagnetic structure in Ce$_5$CoGe$_2$, where multiple experimental techniques reveal complex magnetic moments influenced by various interactions, providing insights into magnetic behavior near superconductivity.

Contribution

The paper identifies and characterizes a noncollinear ferromagnetic order in Ce$_5$CoGe$_2$, highlighting the roles of Dzyaloshinskii-Moriya interactions and crystalline-electric field effects.

Findings

Neutron diffraction shows a noncollinear ferromagnetic structure with four inequivalent Ce sites.

Point-charge model supports different magnetic moments and directions at Ce sites.

Most Ce-Ce bonds have nonzero Dzyaloshinskii-Moriya vectors, indicating complex magnetic interactions.

Abstract

The dense Kondo lattice Ce$_5$CoGe$_2$ exhibits superconductivity once the magnetic ordering is suppressed by pressure. Here the ambient pressure magnetic state is investigated via magnetization, heat capacity, powder neutron diffraction, and muon spin relaxation ($\mu$SR) measurements. Neutron diffraction results reveal a noncollinear ferromagnetic structure, where the four inequivalent Ce sites exhibit different magnetic moments. Point-charge model calculations of the crystalline-electric field (CEF) ground states corroborate different moments between the sites, and suggest sizeable components of the moments along different directions, consistent with the non-collinear structure. Analysis of the Dzyaloshinskii-Moriya (DM) interaction for the bonds connecting Ce atoms demonstrates that most of these bonds exhibit a nonzero DM vector, suggesting that competition between intersite magnetic exchange interactions, CEF driven single-ion anisotropy, the Kondo effect and the DM interaction may drive the non-collinear ferromagnetism.