Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior
Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-point fluctuations, and possible two-dimensional universal behavior
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DOI：
10.1103/physrevb.95.024404
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发表时间：
2017-01-05
影响因子：
3.7
通讯作者：
Manson, J. L.
中科院分区：
文献类型：
--
作者：
Brambleby, J.;Goddard, P. A.;Manson, J. L.
我们提出了在自旋二聚体网络中使用准静态和快速变化的脉冲磁场的玻色超流相的磁和热性质。从热容量的研究得出的熵表明，脉冲场测量是强绝热的性质，并负责一个显着的磁热效应（MCE）的发病。与以前的预测相反，我们表明MCE不仅限于临界区域，但在足够低的温度下，所有大于零的场都会发生。我们解释MCE使用交换耦合二聚体自旋态的热占据的模型，并强调，不考虑这种影响不可避免地会导致不正确的解释实验结果。此外，在我们的材料中的热容量是暗示了一个非凡的贡献，从零点波动，并出现在两个场诱导的临界点，以不同的临界指数表明普遍的行为。在上临界点的数据，结合系统的层状结构，是一致的二维性质的自旋激发系统。
We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system.