Abstract

A number of features, including the appearance of irreversible spontaneous and magnetic-field-induced low temperature transitions accompanied by a relatively sharp increase in magnetization, are identified by analyzing the experimental results obtained in a study of the magnetostructural and magnetocaloric properties of the Mn_{1 – x}Co_xNiGe (0.05 ≤ x ≤ 0.80) system. These transitions are most clearly observed in the concentration range 0.15 ≤ x ≤ 0.40 at temperatures much lower than the characteristic temperatures of second-order isostructural transitions from the paramagnetic hexagonal state to the ferromagnetic hexagonal one. The main purpose of this study is a theoretical analysis of low temperature features against the background of features observed in the entire concentration range 0.05 ≤ x ≤ 0.40. The phenomenological description of the experimental results is based on the concept of a soft mode for structural transitions between hexagonal and rhombic crystal structures when an internal orthogonal field that has an effect on the orthogonal spin component is used in the Heisenberg Hamiltonian. As was found for the spin subsystem within the molecular field approximation and for the structural subsystem within the shifted harmonic oscillator approximation, a number of features comparable to the features experimentally observed for 0.05 ≤ x ≤ 0.1 and 0.1 < x ≤ 0.4 can come to light, which is dependent on the ratio between the orthogonal field and the exchange and structural contributions that describe the interaction of the spin and structural subsystems.

中文翻译：

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Mn1 – xCoxNiGe 系统的磁性和磁热特性的低温特性 (0.05 ≤ x ≤ 0.4)

摘要

_{通过分析 Mn 1} 的磁结构和磁热特性研究中获得的实验结果，确定了许多特征，包括出现不可逆的自发和磁场诱导的低温转变，并伴随着磁化强度的相对急剧增加。_{– x} Co _x NiGe (0.05 ≤ x ≤ 0.80) 系统。在 0.15 ≤ x的浓度范围内可以最清楚地观察到这些转变≤ 0.40，温度远低于从顺磁性六方晶态到铁磁六方晶态的二阶同构转变的特征温度。本研究的主要目的是在整个浓度范围 0.05 ≤ x观察到的特征背景下对低温特征进行理论分析≤ 0.40。当在海森堡哈密顿量中使用对正交自旋分量有影响的内部正交场时，实验结果的唯象描述基于六方晶体和菱形晶体结构之间结构转变的软模式的概念。正如分子场近似中的自旋子系统和位移谐振子近似中的结构子系统所发现的那样，可以发现许多与实验观察到的 0.05 ≤ x ≤ 0.1 和 0.1 < x ≤ 0.4的特征相当的特征，这取决于正交场与描述自旋和结构子系统相互作用的交换和结构贡献之间的比率。