Magnetic Structures and Phase Transformations in Mn-Based CuAu-I Type Alloys

Investigations of the magnetic properties in the ordered $\mathrm{CuAu}‐\mathrm{I}‐\mathrm{type}$ manganese alloys are reviewed. The formation of the ordered phase and the possible magnetic structures are discussed. New experimental results for the Mn‐Ni, Mn‐Pd, and Mn‐Pt systems are reported. Neutron diffraction shows the basic antiferromagnetic structure to be the same for all the alloys investigated. In $\mathrm{MnPt}$ a magnetic‐structure transformation has been observed. Below 800°K the magnetic moments turn from the basal plane gradually to the tetragonal axis. The variation of the transition temperature in the Mn‐Pt system as well as that of the Néel temperature in the Mn‐Ni, Mn‐Pd, and Mn‐Pt systems with concentration were measured and are theoretically analyzed. The dependence of lattice parameters on concentration and temperature was determined. The lattice parameters suffer a significant but continuous change near the Néel temperature which is attributed to Mn‐Mn exchange interaction. Magnetic susceptibility measurements support the neutron‐diffraction results. The increase in susceptibility, observed by several authors at lower temperatures, is found to be a result of contaminations.