Borderline Magnetism: How Adding Mg to Paramagnetic CeCo3 Makes a 450-K Ferromagnet with Large Magnetic Anisotropy

Abstract

A recent experimental study (Phys. Rev. Appl. 9, 024023, 2018) on paramagnetic CeCo3 finds that Magnesium alloying induces a ferromagnetic transition with intrinsic properties large enough for permanent magnet applications. Here we explain these surprising results via a first principles study of the electronic structure and magnetism of Magnesium-alloyed CeCo3. We find the origin of this Magnesium-induced ferromagnetic transition to be Stoner physics -the substantial increase in the Fermi-level density-of-states N (EF ) with Mg alloying. Our calculations suggest that both Ce and Co atoms are important for generating large magnetic anisotropy suggesting the viability of Co-3d, and Ce-4f interaction for the generation of magnetic anisotropy in magnetic materials. These results offer a new route to the discovery of ferromagnetic materials and provide fundamental insight into the magnetic properties of these alloys.

Study of the ferromagnetic quantum phase transition in Ce3−xMgxCo9

“…Although CeCo 3 was identified as a Pauli paramagnetic compound long ago [12], there has been some room for question because of the presence of a low temperature upturn in temperature dependent magnetization [2]. Moreover recent density functional calculation showed CeCo 3 could order ferromagnetically at low temperature [3]. With x ≤ 0.24 of Mg addition, the low temperature magnetization remains temperature independent and manifests Pauli paramagnetism as shown in the inset of Fig.…”

“…Fragile magnetic systems [1] tuned via chemical substitution can lead to quantum criticality, or more generally, a quantum phase transition at 0 K. Here we investigate a Pauli paramagnetic to ferromagnetic quantum phase transition in Ce 3−x Mg x Co 9 [2,3].…”

Robust antiferromagnetism in Y$_2$Co$_3$

“…As Figure 1 suggests, compounds with 60 or more atomic percent of Cobalt are much more often ferromagnetic than antiferromagnetic. While Nature delights in exceptions to such simple classifications, such as the surprisingly paramagnetic CeCo 3 [36][37][38], one would naively expect antiferromagnetic behavior in this stoichiometry regime to be the province of electronegative anions such as Oxygen, Sulfur or the Fluorine group. Yttrium, by contrast, is known substantially for its mineral occurrence with the "rare earth" family, and similar chemical properties, despite its lack of f electrons.…”

Witnessing quantum criticality and entanglement in the triangular antiferromagnet KYbSe$_2$

“…It is noteworthy that this former value is primarily orbital moment, with the Yb orbital moment, at 1.055 𝜇 𝐵 , outstripping the Yb spin moment of 0.572 𝜇 𝐵 (there is an additional small component from the interstitial region, and Se spheres, of 0.12 𝜇 𝐵 ). The exact nature of exchange coupling, as well as the coupling to the lattice depicted by the substantial orbital moment, in such borderline quantum magnets [94,95] remains a matter of substantial debate and controversy.…”