Thermal expansion of ferromagnetic superconductors

We investigate the temperature dependence of thermal expansion of the ferromagnetic triplet superconductors and their thermal expansion coefficients below the superconducting transition temperature of a majority spin conduction band. The free energy of the ferromagnetic superconductors derived by Linder et al. is used. The superconducting gaps in the A2 phase of ^3He and with a node in UGe_2 are considered. By applying Takahashi\u27s method to the free energy, the temperature dependence of the thermal expansion coefficients is studied below the superconducting transition temperature of the majority spin conduction band. We find that we have divergence of the thermal expansion coefficients at the superconducting transition temperatures. The Gruneisen\u27s relation between the temperature dependence of the thermal expansion coefficients and the temperature dependence of the specific heat at low temperatures is satisfied