Thermal expansion of magnetic metals at low temperatures

Measurements have been made from 2 to 30 °K and 60 to 90 °K of the thermal expansion of iron, cobalt and nickel, which show that the Grüneisen parameter γ l for the lattice decreases slightly at low temperatures and that the electronic parameter γ e (calculated from the ratio of the electronic contributions to expansion and heat capacity) is about 2.2. Similar measurements below 30 °K on α-manganese, chromium, face-centred cubic iron-nickel (35-50% Ni) alloys, and Fe 0 5 Mn 0 5 indicate a negative term, proportional to T , in the expansion coefficient. This is particularly large in Invar and in α-manganese. For γ-manganese (+15% Cu) no negative term is observed in the expansion. Results are discussed in terms of electronic and magnetic contributions.