Phase transition regulation, magnetocaloric effect, and abnormal thermal expansion

As a common phenomenon in nature, phase transition has caught people’s attention for a long time. Thus, it has been applied to various fields, such as refrigeration, information and energy storage, and negative thermal expansion. With the virtues of environmental friendliness, high efficiency, noiselessness and easy miniaturization, solid refrigeration technique based on magnetocaloric, electrocaloric, and mechanocaloric effects, is a promising candidate to replace vapor compression technique. Among them, magnetocaloric effect has the longest research history. However, the shortcomings of magnetocaloric effect driven by a single magnetic field limit its solid-state refrigeration application, such as insufficient amplitude of caloric effect, large hysteresis loss, and narrow refrigeration temperature span. To solve these problems, multifield tuning and multicaloric effect came into people's sight. This review introduces our recent research on improving the caloric effect by applying multifield, such as boosting the entropy change, enlarging the transition temperature span, tuning the transition temperature, and lowering the hysteresis losses. Meanwhile, the thermodynamics of multifield and coupled-caloric effect is presented. On the other hand, abnormal thermal expansion (zero thermal expansion, negative thermal expansion) materials have important applications in precision manufacturing. The phase transition and lattice effect dominated by magnetic atoms in the giant magnetocaloric materials with strong magnetic-crystal coupling provide an ideal platform for exploring abnormal thermal expansion. This review also introduces our recent research on abnormal thermal expansion in magnetocaloric materials and prospects relevant research in future.