The low-temperature specific heats of a number of ferromagnetic Pd-Co and Pt-Co alloys

Abstract

Measurements of specific heat have been made in the temperature range 1·4 to 4·2 °K on a series of Pd-Co and Pt-Co alloys. The cobalt content varied between 0·5 and 94·8 at.% in the Pd alloys and was less than 4 at.% in the Pt alloys. In the Pd-Co alloys the temperature dependence of the specific heats was analysed in terms of lattice, electronic, nuclear and magnetic spin wave contributions. From the nuclear contribution, the effective average internal magnetic field Heff at the cobalt nuclei was deduced and found to be approximately proportional to the cobalt concentration. Addition of 0·5% Co to Pd produces an enhancement of about 40% in the total specific heat. This effect is thought to be mainly of magnetic origin. The specific heat values for the Pt-Co alloys were compared with that of platinum and the entropy change ΔS associated with the magnetic disordering was estimated. The results could be represented by ΔS = cR ln (2ST+1) where c is the cobalt concentration and ST has the value 0·8. The Curie temperatures Tc deduced from the specific heat results were found to be approximately half the values reported from magnetization measurements. This is shown to be due mainly to incorrect anlysis of the magnetization data which gives erroneously high values to Tc and to a lesser extent to random variations in solute concentrations in the specimens.