Time and history dependent magnetization has been observed in a wide variety of materials, which are collectively termed as the glassy magnetic systems. However, such systems showing similar non-equilibrium magnetic response can be microscopically very different and they can be distinguished by carefully looking into the details of the observed metastable magnetic behavior. Canonical spin glass is the most well studied member of this class and has been extensively investigated both experimentally and theoretically over the last five decades. In canonical spin glasses, the low temperature magnetic state obtained by cooling across the spin glass transition temperature in presence of an applied magnetic field is known as the field cooled (FC) state. This FC state in canonical spin glass is widely believed as an equilibrium state arising out of a thermodynamic second order phase transition. Here, we show that the FC state in canonical spin glass is not really an equilibrium state of the system. We report careful dc magnetization and ac susceptibility measurements on two canonical spin glass systems, AuMn (1.8%) and AgMn (1.1%). The dc magnetization in the FC state shows clear temperature dependence. In addition, the magnetization shows a distinct thermal hysteresis in the temperature regime below the spin glass transition temperature. On the other hand, the temperature dependence of ac susceptibility has clear frequency dispersion below spin glass transition in the FC state prepared by cooling the sample in the presence of a dc-bias field. We further distinguish the metastable response of the FC state of canonical spin glass from the metastable response the FC state in an entirely different class of glassy magnetic system namely magnetic glass, where the non-equilibrium behavior is associated with the kinetic-arrest of a first order magnetic phase transition.

中文翻译：

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正则自旋玻璃和磁性玻璃的非平衡磁响应

已在多种材料中观察到与时间和历史相关的磁化，这些材料统称为玻璃磁系统。然而，显示类似非平衡磁响应的此类系统在微观上可能非常不同，并且可以通过仔细观察观察到的亚稳态磁行为的细节来区分它们。经典自旋玻璃是这一类中研究最深入的成员，并且在过去的五年中在实验和理论上都得到了广泛的研究。在标准自旋玻璃中，通过在施加磁场的情况下冷却越过自旋玻璃化转变温度而获得的低温磁态称为场冷 (FC) 态。标准自旋玻璃中的这种 FC 状态被广泛认为是由热力学二级相变引起的平衡状态。在这里，我们表明规范自旋玻璃中的 FC 状态并不是系统的真正平衡状态。我们报告了对两种标准自旋玻璃系统 AuMn (1.8%) 和 AgMn (1.1%) 的仔细直流磁化和交流磁化率测量。FC 状态下的直流磁化显示出明显的温度依赖性。此外，在低于自旋玻璃化转变温度的温度范围内，磁化强度显示出明显的热滞后。另一方面，在通过在直流偏置场存在下冷却样品制备的 FC 状态下，交流磁化率的温度依赖性在自旋玻璃化转变以下具有明显的频率色散。