Abstract
The total entropy change in the first-order magnetic phase transition materials is mainly composed of lattice entropy change (LEC) and magnetic entropy change (MEC). Generally, the MEC is limited by the total angular momentum quantum number, while the LEC is related to the volume change associated with phase transition and it can be easily regulated. Therefore, maximizing LEC is considered as an effective means to improve the refrigeration performance. However, the current research methods only calculate the LEC between two stable phases after phase transition, whereas the LEC during phase transformation is not fully clarified. Here, the mixed Debye temperature (MDT) model and the mixed lattice entropy (MLE) model are proposed based on the two-phase coexistence mechanism for calculating the LEC during the magnetic field-driven phase transition in Gd5Ge4. Both models indicate that the lattice entropy strongly depends on the applied magnetic field during phase transformation. According to the MLE model, which shows better accuracy, a large LEC up to –22.31 Jkg-1K−1 at 25 K can be exerted in Gd5Ge4 by a relatively small magnetic field of 2.5 T. Our proposed theoretical models are helpful for designing high-performance magnetic refrigerants.
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