Ce$_{3-x}$Mg$_x$Co$_{9}$: transformation of a Pauli paramagnet into a strong permanent magnet

TL;DR

This study demonstrates that substituting Mg into CeCo$_3$ transforms it from a Pauli paramagnet into a strong, high-temperature ferromagnet with significant magnetic anisotropy, offering new avenues for inexpensive permanent magnet development.

Contribution

It reveals that Mg substitution induces ferromagnetism in Ce$_{3-x}$Mg$_x$Co$_9$, with high Curie temperatures and magnetic anisotropy, a novel approach for permanent magnet materials.

Findings

Ferromagnetism appears at low Mg substitution levels.

Curie temperature reaches up to 450 K.

Large axial magnetic anisotropy observed.

Abstract

We report on the synthesis of single crystalline and polycrystalline samples of Ce$_{3-x}$Mg$_x$Co$_9$ solid solution ($0\leq x \lesssim 1.4$) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6\textit{c} site of the CeCo$_3$ structure. Ferromagnetism is induced by Mg substitutions starting as low as $x=0.18$ and reaching a Curie temperature as high as $450$\,K for $x=1.35$. Measurements on single crystals with $x=1.34$ and $T_\textrm{C}=440$\,K indicate an axial magnetic anisotropy with the anisotropy field of $6$\,T and a magnetization of $6$\,$\mu_B/$f.u. at $300$\,K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests other non-magnetic phases, similar to CeCo$_3$, may also conceal nearby ferromagnetic phases.