Finite-size effects at diamagnetic phase transitions and in the Condon domain phase

The diamagnetic phase transition in a sample of finite thickness (thin film) is studied. It is shown that changing the film thickness is equivalent to shifting the diamagnetic phase-transition to a lower temperature. Calculations of the effect of the Condon domain influence on the specific heat temperature jump at second-order diamagnetic phase transition in a slab are performed. The contribution from the domain walls and demagnetization effects to the jump in specific heat at the phase transition is shown to be independent of the slab thickness. We calculate the critical sample size for the diamagnetic phase-transition existence, i.e., the film thickness, below which the order parameter of the diamagnetic phase transition is zero. The compressibility increase observed in beryllium and occurring as a result of the domain formation is qualitatively explained.