Magnetic phase diagram of the semi-Heusler alloys from first-principles

TL;DR

This study maps the magnetic phases of Mn-based semi-Heusler alloys at zero temperature using first-principles calculations, revealing how electron characteristics influence magnetic interactions and phases.

Contribution

It provides a detailed first-principles analysis of magnetic phase diagrams in semi-Heusler alloys, highlighting the roles of conduction electrons and unoccupied Mn 3d states.

Findings

RKKY-like ferromagnetism occurs with high conduction electron spin polarization.

Antiferromagnetic superexchange dominates when unoccupied Mn 3d states are near the Fermi level.

Results agree well with experimental observations.

Abstract

The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined at T=0 using first-principles calculations in conjunction with the frozen-magnon approximation. We show that the magnetism in these systems strongly depends on the number of conduction electrons, their spin polarization and the position of the unoccupied Mn 3d states with respect to Fermi energy. Various magnetic phases are obtained depending on these characteristics. The conditions leading to diverse magnetic behavior are identified. We find that in the case of a large conduction electron spin polarization and the unoccupied Mn 3d states lying far above the Fermi level, an RKKY-like ferromagnetic interaction is dominating. On the other hand, the antiferromagnetic superexchange becomes important in the presence of large peaks of the unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic behavior depends on the competition of these two exchange mechanisms. The obtained results are in very good agreement with the available experimental data.