The jungle of experimental behaviors of spin-crossover materials contains a tremendous number of unexpected behaviors, among which, the unsymmetrical hysteresis loops having different shapes on heating and cooling, that we often encounter in literature. Excluding an extra effect of crystallographic phase transitions, we study here these phenomena from the point of view of elastic modeling and we demonstrate that a simple model accounting for the bond lengths misfits between the high-spin and low-spin states is sufficient to describe the situation of unsymmetrical hysteresis showing plateaus at the transition only on cooling or on heating branches. The idea behind this effect relates to the existence of a discriminant elastic frustration in the lattice, which expresses only along the high-spin to low-spin transition or in the opposite side. The obtained two-step transitions showed characteristics of self-organization of the spin states under the form of stripes, which we explain as an emergence process of antagonist directional elastic interactions inside the lattice. The analysis of the spin state transformation inside the plateau on cooling in terms of two sublattices demonstrated that the elastic-driven self-organization of the spin states is accompanied with a symmetry breaking.

中文翻译：

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自旋交叉材料中非对称热滞回的弹性起源：对称破坏的证据

自旋交越材料的实验行为的丛林包含了许多意想不到的行为，其中，不对称的磁滞回线在加热和冷却时具有不同的形状，这是我们在文献中经常遇到的。除了结晶相变的额外影响外，我们从弹性建模的角度研究了这些现象，并证明了一个简单的模型来解释高自旋态和低自旋态之间的键长不匹配。出现非对称磁滞的情况，仅在冷却或加热分支时才显示出平稳状态。这种效果背后的想法与晶格中存在区别性的弹性挫折感有关，该挫折感仅沿从高旋转到低旋转的过渡或相反的一侧表示。所获得的两步转变显示了条带形式下自旋态的自组织特性，我们将其解释为晶格内部拮抗性方向弹性相互作用的出现过程。根据两个子晶格对高原内部自旋状态转变的分析表明，自旋态的弹性驱动自组织伴随着对称破坏。