Structural, electronic, and magnetic properties of tetragonalMn3−xGa: Experiments and first-principles calculations

Abstract

This work reports on the electronic, magnetic, and structural properties of the binary intermetallic compounds ${\mathrm{Mn}}_{3\ensuremath{-}x}\mathrm{Ga}$. The tetragonal ${\mathrm{DO}}_{22}$ phase of the ${\mathrm{Mn}}_{3\ensuremath{-}x}\mathrm{Ga}$ series, with $x$ varying from 0 to 1.0 in steps of $x=0.1$, was successfully synthesized and investigated. It was found that all these materials are hard magnetic, with energy products ranging from $10.1\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$ for low Mn content $(x\ensuremath{\rightarrow}1)$ to $61.6\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$ for high Mn content $(x\ensuremath{\rightarrow}0)$. With decreasing Mn content, the average saturation magnetization per atom increases from $0.26{\ensuremath{\mu}}_{B}$ for ${\mathrm{Mn}}_{3}\mathrm{Ga}$ to $0.47{\ensuremath{\mu}}_{B}$ for ${\mathrm{Mn}}_{2}\mathrm{Ga}$. The increase in the saturation magnetization as the Mn content is reduced indicates a ferrimagnetic order with partially compensating moments of the two different Mn atoms on the two crystallographically different sites of the ${\mathrm{DO}}_{22}$ structure. This type of magnetic order is supported by ab initio calculations of the electronic structure that predict a nearly half-metallic ferrimagnet with the highest spin polarization of 88% at the Fermi energy for ${\mathrm{Mn}}_{3}\mathrm{Ga}$. The Curie temperature of the compounds is restricted to approximately $770\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ because of a structural phase transition to the hexagonal ${\mathrm{DO}}_{19}$ phase. Thermal irreversibilities between zero-field-cooled and field-cooled measurements suggest that the ${\mathrm{Mn}}_{3\ensuremath{-}x}\mathrm{Ga}$ series belongs to the class of magnetically frustrated ferrimagnets. The most pronounced magnetic anomaly is found for ${\mathrm{Mn}}_{3}\mathrm{Ga}$.