Field dependence of the magnetic entropy change in typical materials with a second-order phase transition

Magnetic field dependence of the magnetic entropy change (Delta S) is the key for magnetic refrigeration. For magnetic materials with a second-order phase transition, the experimental data can be well fitted by the formula of Delta S = -kM(s)(0)h(2/3)-S(0,0) for a practical field change from 0 to h (the reduced field), where M-s(0) is the spontaneous magnetization at 0K. The constant k is approximately equal to 1.00T/K, and S(0,0) is interestingly found to be negative. The formula is discussed based on the renormalization group approach to scaling. The attempts have also been made using the formula for NaZn13-type La(Fe,Si)(13) compounds with a magnetic first-order phase transition. (C) 2007 Elsevier B.V. All rights reserved.