Exchange interactions and Curie temperatures in Mn2CoZ compounds

TL;DR

This study investigates magnetic interactions and predicts high Curie temperatures in Mn2CoZ compounds with the Hg2CuTi structure, revealing how chemical composition and pressure influence their magnetic properties.

Contribution

The paper provides first principles calculations of exchange interactions and Curie temperatures in Mn2CoZ compounds, highlighting the role of direct Mn-Mn exchange and pressure effects.

Findings

Curie temperatures exceed 800 K for certain Mn2CoZ compounds.

Direct Mn-Mn exchange decreases Curie temperature when Z varies.

Pressure reduces Curie temperature by decreasing magnetic moments.

Abstract

The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) with the Hg2CuTi structure are of large interest due to their half-metallic ferrimagnetism. The complex magnetic interactions between the constituents are studied by first principles calculations of the Heisenberg exchange coupling parameters, and Curie temperatures are calculated from those. Due to the direct Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while the total moment increases when changing Z from one group to another. The exchange interactions are dominated by a strong direct exchange between Co and its nearest neighbor Mn on the B site, which is nearly constant. The coupling between the nearest-neighbor Mn atoms scales with the magnetic moment of the Mn atom on the C site. Calculations with different lattice parameters suggest a negative pressure dependence of the Curie temperature, which follows from decreasing magnetic moments. Curie temperatures of more than 800 K are predicted for Mn2CoAl (890 K), Mn2CoGa (886 K), and Mn2CoIn (845 K).