Activation Volumes of Interstitial Diffusion in Ferromagnetic Metals and Alloys

The disaccommodation technique was used to determine the activation volumes of carbon diffusion ΔV of a Fe-1.4 wt% Si alloy, of hcp cobalt, and of nickel at the temperatures of -21, 75, and 110^∘{}C, respectively. The obtained values of ΔV are +0.3 ±{} 0.3 and -0.6 ±{} 0.9 cm³ mole^-1 for the two relaxations observed in hcp cobalt, and 1.2 ±{} 0.1 cm³ mole^-1 for nickel. These results are discussed in terms of a continuum model that interprets the activation energy of diffusion as a sum of the strain and exchange energies. It is found that in ferromagnetic solids the activation volume of diffusion is essentially controlled by the ferromagnetic anharmonicity.