The second-order conventional and first-order inverse magnetocaloric effects (MCEs) in Ni–Mn-based quaternary Heusler alloys have been systematically investigated by means of the lock-in thermography technique, which enables the direct measurement of the MCE-induced temperature change in a periodic magnetic field. Through systematic measurements of the temperature dependence of the MCE signals, the tuning of the conventional and inverse MCEs with temperature for the same Heusler alloys has been demonstrated, where the phase transitions responsible for the MCEs are clearly distinguished. The lock-in thermography measurements show that some Ni–Mn-based Heusler alloys exhibit much smaller temperature changes due to the inverse MCEs in the periodic field as compared to the conventional MCEs, even though they exhibit a larger magnetic entropy change across the first-order transition responsible for the inverse MCEs. We discuss the origin of this behavior in terms of the field-induced entropy change and thermal hysteresis of the alloys. These findings will be useful not only in accelerating the optimization of inverse MCE materials but also in understanding the mechanism of the MCEs.

中文翻译：

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使用锁定热成像技术同时直接测量Ni-Mn基Heusler合金中常规和逆磁热效应

利用锁定热成像技术系统研究了Ni-Mn基四元Heusler合金中的二阶常规和一阶逆磁热效应（MCEs），该技术可直接测量MCE引起的温度变化在周期性磁场中。通过对MCE信号的温度依赖性进行系统的测量，已证明了相同Heusler合金对常规MCE和逆MCE随温度的调谐，其中清楚地区分了引起MCE的相变。锁定热像仪测量结果表明，与常规MCE相比，某些Ni-Mn基Heusler合金由于周期性场中的逆MCE而具有较小的温度变化，即使它们在负责逆MCE的一阶跃迁上表现出较大的磁熵变化。我们根据合金的场致熵变和热磁滞来讨论这种行为的起源。这些发现不仅有助于加速逆MCE材料的优化，而且有助于理解MCE的机理。