Effect of magnetic field on the heat capacity ofNi3Al alloys

The heat capacity C of three alloys of nominal composition ${\mathrm{Ni}}_{74}$ ${\mathrm{Al}}_{26}$, ${\mathrm{Ni}}_{74.25}$ ${\mathrm{Al}}_{25.75}$, and ${\mathrm{Ni}}_{74.5}$ ${\mathrm{Al}}_{25.5}$ (hereafter, alloys I, II, and III, respectively) has been measured in zero and applied fields of 2.5, 5.3, 7.5, and 9.8 T in the range 1.5–20 K. The zero-field C/T-versus-$T^2$ plots show a mild upturn in all three alloys at temperatures below ∼10 K. No discernible effect on heat capacity is observed in the 2.5-T field for alloys I and II, and only at higher fields does the upturn get suppressed. In the maximum applied field of 9.8 T, the C/T-versus-$T^2$ plots are linear. For alloy III (magnetization measurements at 4.2 K show this material to be magnetically ordered), the upturn is completely removed in the 2.5-T field and the heat capacity decreases progressively in increasing applied fields at all temperatures. The origin of the upturn in C/T is discussed as arising from either spin fluctuations or magnetic clusters. While the zero-field data can be interpreted using either of the two models, the data obtained in applied fields strongly suggest that the upturn in C/T plots is caused by spin fluctuations and that spin fluctuations in these materials are depressed in applied magnetic fields.