双铁磁耦合链状化合物MnNi（NO $_2$）PDMATHAAE（en）$_2$（en =乙二胺）的specific heat的链间平均场论
Numerical interchain mean-field theory for the specific heat of the bimetallic ferromagnetically coupled chain compound MnNi(NO$_2$)$_4$(en)$_2$ (en = ethylenediamine)
摘要：
本文详细地研究了MnNi（NO $_2$）$_4$（en）$_2$（en =乙二胺）的比热随场的变化.对于这种材料，在零场反铁磁低于$T_N=2.45$ K，小场抑制磁序。相反，在这样的领域中的双峰状结构的比热的温度依赖性观察。我们将这种行为归因于自旋波色散中存在的声学和光学模式，这是由于每个单元格存在两种不同的自旋。我们比较我们的实验数据的数值计算结果，通过精确的对角化和量子蒙特卡罗模拟交替自旋链模型，使用参数，已来自高温行为的磁化率的比热。链间耦合被包括在平均场水平的数值处理。我们观察到显着的实验和理论之间的协议，包括有序过渡，使用先前确定的参数。此外，所观察到的施加磁场对MnNi（NO $_2$）$_4$（en）$_2$有序态的强烈影响预示着有趣的磁热性质。
英文摘要：
We present a detailed study of the field-dependent specific heat of the bimetallic ferromagnetically coupled chain compound MnNi(NO$_2$)$_4$(en)$_2$, en = ethylenediamine. For this material, which in zero field orders antiferromagnetically below $T_N=2.45$ K, small fields suppress magnetic order. Instead, in such fields a double-peak like structure in the temperature dependence of the specific heat is observed. We attribute this behavior to the existence of an acoustic and an optical mode in the spin wave dispersion as result of the existence of two different spins per unit cell. We compare our experimental data to numerical results for the specific heat obtained by exact diagonalization and Quantum-Monte-Carlo simulations for the alternating spin chain model, using parameters that have been derived from the high-temperature behavior of the magnetic susceptibility. The interchain coupling is included in the numerical treatment at the mean-field level. We observe remarkable agreement between experiment and theory, including the ordering transition, using previously determined parameters. Furthermore, the observed strong effect of an applied magnetic field on the ordered state of MnNi(NO$_2$)$_4$(en)$_2$ promises interesting magnetocaloric properties.
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