Understanding Mechanisms in Magneto-Structural Transformations

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Refrigeration and building cooling account for 17 percent of total electricity consumption in the US. High efficiency magnetic refrigerants, which heat up or cool down in response to external magnetic fields, have the potential to replace traditional vapor-compression refrigerators and heat pumps, dramatically reducing electricity consumption and radically altering the domestic energy landscape. However, these materials are currently limited by energy loss that occurs every time the magnetic field is changed, associated with abrupt changes in the internal structure of the material. This award supports research into the microscopic mechanism causing this energy loss, in order to understand its fundamental origin. This research will result in a better understanding of how to design high-efficiency near-room temperature magnetic refrigerants. Such knowledge could also improve the design of other functional materials such as shape memory alloys.Hysteresis plays a critical role in limiting the efficiency of functional solid-solid phase transitions. While substantial theory has been developed to design low-hysteresis first-order phase transitions in thermoelastic martensites, it remains unclear why certain materials systems exhibit significantly larger hysteresis than other systems. This research seeks to investigate the phase transformation mechanisms in Fe2P alloys, which can exhibit hysteresis 1 K, with the objective of identifying the origins of hysteresis in that system. The research plan consists of three goals: 1) Identify microscopic transformation mechanisms in first-order magneto-structural phase transitions in Fe2P alloys, and detect processes that could significantly contribute to hysteresis; 2) Elucidate the origin of hysteresis and its relationship to a shift from first-order to second-order transition behavior; and 3) Analyze magnetic refrigerant cycle-based performance for low-hysteresis alloys. This research aims to achieve a rational approach to design new low-hysteresis Fe2P alloys, and may additionally provide greater insight into hysteresis engineering in other solid-solid phase transitions.