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

Investigations of the magnetic properties in the ordered CuAu-I-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 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.