Evolution of Magnetic Order from the Localized to the Itinerant Limit

We report the discovery of CaMn₂Al₁₀, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83_μB/Mn, significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈ 9% of Rln2. 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 χ is anisotropic below 20 K, with a maximum ratio of χ_[010]/χ_[001] ≈ 3.5. A strong power-lawmore » divergence χ(T) ~ T^–1.2 below 20 K implies incipient ferromagnetic order, an Arrott plot analysis of the magnetization suggests a vanishing low Curie temperature T_C ~ 0. Our experiments indicate that CaMn₂Al₁₀ is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.