Yang Junjie, Samarakoon Anjana, Dissanayake Sachith, Ueda Hiroaki, Klich Israel, Iida Kazuki, Pajerowski Daniel, Butch Nicholas P, Huang Q, Copley John R D, Lee Seung-Hun
Department of Physics, University of Virginia, Charlottesville, VA 22904;
Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan;
Proc Natl Acad Sci U S A. 2015 Sep 15;112(37):11519-23. doi: 10.1073/pnas.1503126112. Epub 2015 Aug 31.
Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.
自从在稀磁系统中发现自旋玻璃以来，对其研究主要集中在理解随机性和缺陷作为驱动机制。同样的范式也被用于解释在致密受挫系统中发现的玻璃态。然而，最近从理论上表明，不同的机制，如量子涨落和拓扑特征，可能在远离传统稀释极限的无缺陷自旋系统中诱导玻璃态。在此，我们报告了在受挫磁体的纯净极限附近存在一种玻璃态（我们称之为自旋阻塞）的实验证据，该玻璃态对低浓度缺陷不敏感。我们研究了杂质对高度受挫磁体SrCr9pGa12 - 9pO19 [SCGO(p)]的影响，其中磁性Cr(3+)（s = 3/2）离子形成了一个准二维双锥体三角系统。我们的实验数据表明，随着非磁性Ga(3+)杂质浓度的变化，存在两种不同的玻璃态相：对于高磁性浓度区域（p > 0.8），是一种奇异的玻璃态，我们称之为自旋阻塞；对于较低磁性浓度（p < 0.8），是一种团簇自旋玻璃。这一观察结果表明，自旋阻塞是理解致密受挫磁体玻璃态类别的一个独特视角。
