Wu Weida, Israel Casey, Hur Namjung, Park Soonyong, Cheong Sang-Wook, de Lozanne Alex
Department of Physics, University of Texas, Austin, Texas 78712, USA.
Nat Mater. 2006 Nov;5(11):881-6. doi: 10.1038/nmat1743. Epub 2006 Oct 8.
Spin glasses are founded in the frustration and randomness of microscopic magnetic interactions. They are non-ergodic systems where replica symmetry is broken. Although magnetic glassy behaviour has been observed in many colossal magnetoresistive manganites, there is no consensus that they are spin glasses. Here, an intriguing glass transition in (La,Pr,Ca)MnO3 is imaged using a variable-temperature magnetic force microscope. In contrast to the speculated spin-glass picture, our results show that the observed static magnetic configuration seen below the glass-transition temperature arises from the cooperative freezing of the first-order antiferromagnetic (charge ordered) to ferromagnetic transition. Our data also suggest that accommodation strain is important in the kinetics of the phase transition. This cooperative freezing idea has been applied to structural glasses including window glasses and supercooled liquids, and may be applicable across many systems to any first-order phase transition occurring on a complex free-energy landscape.
自旋玻璃是由微观磁相互作用的受挫和随机性产生的。它们是非遍历系统，其中副本对称性被打破。尽管在许多巨磁阻锰氧化物中都观察到了磁性玻璃行为，但对于它们是否为自旋玻璃尚无定论。在此，利用可变温度磁力显微镜对(La,Pr,Ca)MnO3中一个有趣的玻璃转变进行了成像。与推测的自旋玻璃图景相反，我们的结果表明，在玻璃转变温度以下观察到的静态磁构型源于一级反铁磁（电荷有序）到铁磁转变的协同冻结。我们的数据还表明，调节应变在相变动力学中很重要。这种协同冻结的观点已应用于包括窗玻璃和过冷液体在内的结构玻璃，并且可能适用于许多系统中发生在复杂自由能景观上的任何一级相变。
