Transition from Ferromagnetism to Paramagnetism in Ni–Cu Alloys

The low‐temperature (1.4° to 4.2°K) specific heat, the ferromagnetic Curie temperature, and the magnetic moment of Ni–Cu solid solutions were measured near the composition where ferromagnetism terminates. The anomaly in the specific heat cannot be accounted for by the bT³ ln T term expected from electron‐paramagnon interaction, but it can be interpreted as a magnetic cluster contribution independent of temperature from 1.4° to 4.2°K. Another magnetic contribution is included in the term of the specific heat linear in temperature. Whether the maximum in the linear term at 50–54 at.% Cu should be attributed to this magnetic contribution or to the (enhanced) electronic specific heat is uncertain. For alloys near the critical composition the Curie temperature, as determined by methods based on high field data, is distinctly higher than that measured at low fields.