In this work, an overview of the Weiss molecular mean-field theory, the Bean–Rodbell model and the Landau theory is presented, providing the theoretical background for simulating the magnetocaloric properties for La_0.6Ca_0.2Na_0.2MnO₃ manganite. Results showed that sample exhibits second-order ferromagnetic (FM)–paramagnetic (PM) magnetic phase transition and relatively higher values of magnetic entropy change (−∆S_M). In application point of view, this material can be used in magnetic refrigeration technology. The theoretical values of −∆S_M determined using each theory agree well with the experimental ones estimated from Maxwell relations. In other part, a good agreement in the spontaneous magnetization values, M_spont(T), estimated from (−∆S_M vs. M²) and (H/M vs. M²) data was found. Also, the values of the critical exponent (β) found from both methods are close and check that the mean-field model is adequate to study the MCE in La_0.6Ca_0.2Na_0.2MnO₃ sample.

中文翻译：

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La 0.6 Ca 0.2 Na 0.2 MnO 3锰矿化合物理论模型的磁热效应研究

在这项工作中，将对Weiss分子均场理论，Bean-Rodbell模型和Landau理论进行概述，为模拟La _0.6 Ca _0.2 Na _0.2 MnO ₃锰矿的磁热性质提供理论背景。结果表明，样品表现出二阶铁磁（FM）-paramagnetic（PM）的磁相变和磁熵变的相对较高的值（- ΔS_中号）。从应用的角度来看，该材料可用于磁性制冷技术。− ∆S _M的理论值使用每种理论确定的结果与根据麦克斯韦关系估算的实验结果非常吻合。在其他部分，在自发磁化值的良好的一致性，中号_小号蓬（Ť（）中，从估计- ΔS_中号对中号²）和（ħ /中号对中号²）的数据被发现。而且，从这两种方法得出的临界指数（β）值都接近，并检查平均场模型是否足以研究La _0.6 Ca _0.2 Na _0.2 MnO ₃样品中的MCE 。