Magnetic entropy calculation for a second-order ferromagnetic phase transition

In this paper, we present a new calculation method of magnetic entropy in an arbitrary second-order ferromagnetic phase transition system. Based on the Arrott-Noakes relation (H/M)(1/gamma) = (T -T-C)/T-C + (M/M-1)(1/beta), the Gibbs energy can be rewritten as a new form where the critical exponents are naturally included. Correspondingly, the magnetic entropy (S-M) is presented as: S-M = -[1/1/gamma+1 partial derivative A'/partial derivative T M1/gamma+1 + 1/1/beta+1/gamma+1 partial derivative B'/partial derivative T M1/beta+1/gamma+1]H1-1/gamma. Thus, the magnetic entropy change (Delta S-M) can be deduced as Delta S-M vertical bar T=T-C similar to H1+beta-1/beta+gamma. which is consistent exactly with the previous report [V. Franco et al., Appl. Phys. Lett. 89 (2006) 222512]. In addition, the conventional calculation method of magnetic entropy can be treated as a particular form of this calculation method. Furthermore, the obtained magnetic entropy change from experimental measurement are consistent with the theoretical value deduced from the present method.