Dpto. Física de la Materia Condensada ICMSE-CSIC, Universidad de Sevilla, Apdo1065, 41080, Sevilla, Spain.
Institut für Materialwissenschaft, Technische Universität Darmstadt, Alarich-Weiss-Str. 16, 64287, Darmstadt, Germany.
Nat Commun. 2018 Jul 11;9(1):2680. doi: 10.1038/s41467-018-05111-w.
The ideal magnetocaloric material would lay at the borderline of a first-order and a second-order phase transition. Hence, it is crucial to unambiguously determine the order of phase transitions for both applied magnetocaloric research as well as the characterization of other phase change materials. Although Ehrenfest provided a conceptually simple definition of the order of a phase transition, the known techniques for its determination based on magnetic measurements either provide erroneous results for specific cases or require extensive data analysis that depends on subjective appreciations of qualitative features of the data. Here we report a quantitative fingerprint of first-order thermomagnetic phase transitions: the exponent n from field dependence of magnetic entropy change presents a maximum of n > 2 only for first-order thermomagnetic phase transitions. This model-independent parameter allows evaluating the order of phase transition without any subjective interpretations, as we show for different types of materials and for the Bean-Rodbell model.
理想的磁热材料应该处于一级相变和二级相变的边界。因此，明确确定相变的顺序对于应用磁热研究以及其他相变材料的表征都是至关重要的。尽管 Ehrenfest 提供了一个概念上简单的相变顺序定义，但基于磁测量的已知确定方法要么在特定情况下提供错误的结果，要么需要依赖于对数据定性特征的主观评价的广泛数据分析。在这里，我们报告了一级热磁相变的定量特征：仅对于一级热磁相变，磁场对磁熵变化的依赖关系中的指数 n 呈现最大值 n>>2。这个与模型无关的参数允许在没有任何主观解释的情况下评估相变的顺序，我们将在不同类型的材料和 Bean-Rodbell 模型中展示这一点。
