Correlation of Electronic Specific Heats and Curie Temperatures in Dilute Alloys of Iron

Abstract

If itinerant electrons play an important role in ferromagnetism, one might expect some correlation between the magnetic parameters, e.g., the strength of the exchange interactions and the density of electronic states as revealed by low-temperature specific heat measurements. Such a correlation is looked for in Fe alloys with small amounts of Ti, V, Cr, Mn, Co, Ni, Al, Si, Mo, and W. The quantity (1/γ)dγ/dc, where γ is the coefficient of the term in the specific heat which is linear in temperature and c is the solute concentration, is determined for these alloy systems. This quantity is compared with the similar derivatives for such quantities as spontaneous magnetization, Curie temperature, lattice parameter, and electrical resistivity. The correlation with Curie temperature is significant. Ti, V, Cr. W, and Co all raise the Curie temperature and depress the electronic specific heat, while Mn, Ni, Al, and Si lower the Curie temperature and increase the electronic specific heat. Mo is the exception producing a slight decrease in both the quantities. The measurements of specific heat are carried out using simultaneous calorimetry on three samples, one of pure iron, one with one percent solute, and one with two percent solute. The cancellation of errors achieved in this manner permits the measurement of a Δγ/γ of one percent to a precision of about ten percent. Brailsford's formulation of the dilute alloy specific heat problem is applied to a ferromagnetic solvent. It appears that the ``rigid band'' terms are not sufficient to account for the experimental results.