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arXiv 0903.2772cond-mat.stat-mechcond-mat.other
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旋转冰上

Spin Ice

Michel J. P. Gingras

摘要:

几何阻挫通常出现在包含磁矩(自旋)的系统中,这些磁矩(自旋)位于由基本三角形或四面体单元组成的晶格的位置上,并且通过反铁磁最近邻交换相互作用。尽管不太常见,但几何挫折也可能出现在具有强非共线单离子易轴(类伊辛)各向异性和铁磁耦合自旋的系统中。这就是在某些烧绿石氧化物材料中发生的情况,其中类伊辛磁性稀土磁矩(Ho $^{3+}$、Dy $^{3+}$)位于角共享四面体的晶格上,并且通过有效的铁磁(偶极)相互作用耦合。这些系统具有宏观数量的准简并经典基态,并显示出广泛的低温熵密切相关的广泛的质子在普通的水冰无序熵。因此,这些磁系统被称为{ \it自旋冰}。本章回顾了磁性烧绿石氧化物中自旋冰现象的基本成分。

英文摘要:

Geometric frustration usually arises in systems that comprise magnetic moments (spins) which reside on the sites of a lattice made up of elementary triangular or tetrahedral units and which interact via antiferromagnetic nearest-neighbor exchange. Albeit much less common, geometric frustration can also arise in systems with strong non-collinear single-ion easy-axis (Ising-like) anisotropy and ferromagnetically} coupled spins. This is what happens in some pyrochlore oxide materials where Ising-like magnetic rare earth moments (Ho$^{3+}$, Dy$^{3+}$) sit on a lattice of corner-shared tetrahedra and are coupled via effectively ferromagnetic (dipolar) interactions. These systems possess a macroscopic number of quasi-degenerate classical ground states and display an extensive low-temperature entropy closely related to the extensive proton disorder entropy in common water ice. For this reason, these magnetic systems are called {\it spin ice}. This chapter reviews the essential ingredients of spin ice phenomenology in magnetic pyrochlore oxides.

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