Particle Size Effects on Calorimetric and Magnetic Properties of the Ferromagnetic Phase in the Eutectic Composite Alloy of ZnSnAs2–MnAs System

Resumo

Magnetic and calorimetric properties of a eutectic alloy of ZnSnAs₂–MnAs system are studied depending on particle size in the range of magnetostructural transition temperatures of the ferromagnetic phase MnAs. The particle sizes are varied by using different cooling rates as measured by a temperature-control device. The cooling rate is ~0.05°C/s under ordinary conditions and ~90°C/s under quenching with salt systems having high heat conductivity. Simultaneous phase solidification, typical of eutectics, under high cooling rates yields nanosized (≤50 nm) MnAs grains. DSC curves for quenched samples, unlike for samples prepared under ordinary conditions, have no thermal feature associated with α–β-MnAs magnetostructural transformation. The magnetization and Curie temperature have considerably different values in quenched samples and in samples prepared in an ordinary manner. The Curie temperature rises to 337 K and the coercive force increases as the particle size increases.