Gruneisens Approach to Magnetovolume Effect of Itinerant Electron Ferromagnets

Interplay between magnetism and crystal volume in itinerant electron ferromagnets is reexamined paying particular attention on effects of spin fluctuations. By introducing Gruneisen parameters, magnetovolume properties are derived from the explicit volume dependence of the free energy. As the result, we have clarified the presence of new thermal expansions, giving rise to the enhanced T-linear coefficient of the thermal expansion coefficient at low temperatures around the magnetic instability point. We have also found that the magnetovolume coupling constant is temperature dependent and vanishes at the critical point. These results are compared with experiments.