CaMn$_2$Al$_{10}$: itinerant Mn magnetism on the verge of ferromagnetic order

TL;DR

The paper reports the discovery of CaMn$_2$Al$_{10}$, a weak itinerant Mn magnet with strong anisotropy and proximity to ferromagnetic order, supported by experimental and theoretical evidence of itinerant magnetism and low Curie temperature.

Contribution

It introduces CaMn$_2$Al$_{10}$ as a new Mn-based weak itinerant magnet near ferromagnetic order, combining experimental measurements and density functional theory analysis.

Findings

Mn magnetism is highly itinerant with reduced magnetic moment.

Magnetic susceptibility shows strong anisotropy and divergence below 20 K.

The material is on the verge of ferromagnetic order with an estimated Curie temperature near zero.

Abstract

We report the discovery of \CMA, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of $0.83\,\mathrm{\mu_B}$/Mn, significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only $\approx 9$ \% of $R \mathrm{ln}\,2$. These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility $\chi$ is anisotropic below 20 K, with a maximum ratio of $\chi_{[010]}/\chi_{[001]}\approx 3.5$. A strong power-law divergence $\chi(T)\sim T^{-1.2}$ below 20 K implies incipient ferromagnetic order, and an Arrott plot analysis of the magnetization suggests a vanishingly low Curie temperature $T_C\sim 0$. Our experiments indicate that \CMA~is a rare example of a Mn-based weak itinerant magnet that is poised on the verge of ferromagnetic order.