Magnetic Interactions in Disordered Ni‐Mn Alloys Near the 25% Mn Composition

The magnetization of ${\mathrm{Ni}}_{\text{1−}\mathrm{x}}{\mathrm{Mn}}_{\mathrm{x}}$ alloys ($\text{0.22\hspace{0.17em}<\hspace{0.17em}}\mathrm{x}\text{\hspace{0.17em}<0.32}$ ), disordered by quenching from 1000°C, has been studied as a function of field (0 – 100 kOe), temperature (4 – 300K), and field cooling history. For zero‐field cooling, the temperature dependence of the initial susceptibility indicates an extrapolated Curie temperature which is negative for $\mathrm{x}\text{\hspace{0.17em}>\hspace{0.17em}0.25}$ , near zero for $\mathrm{x}\text{\hspace{0.17em}∼\hspace{0.17em}0.25}$ and positive for $\mathrm{x}\text{\hspace{0.17em}<\hspace{0.17em}0.25}$ . Magnetization data (4 – 300K) for field cooling (8 kOe) and zero‐field cooling indicate that the net moment induced by field cooling peaks at the ${\mathrm{Ni}}_3\mathrm{Mn}$ composition. Further high field data (0 – 100 kOe) indicate that measuring fields in excess of 50 kOe at 4K are sufficient to eliminate the difference in magnetization for field cooling and zero‐field cooling. The data can be qualitatively explained by a simple three phase model, in which Mn‐rich, stoichiometric ${\mathrm{Ni}}_3\mathrm{Mn}$ , and Mn‐deficient units with varying properties couple to yield the observed behavior.