Two-Dimensional Magnetic Materials

One big difference between one- and two-dimensional systems is that whereas the former never order above 0 K (without interchain interactions), it is possible for a two-dimensional Ising system to order at finite temperature. Onsager has examined such a system for S = 1/2 and found theoretical evidence for ordering, on a square lattice and even if the coupling anisotropy in the two directions on a quadratic lattice (defined to be ]/] ) is 100. An example that behaves as a two-dimensional Ising antiferromagnet is CsslCoBrs].  

The magnetic properties of these assemblies as multilayers are similar to their bulk counterparts, but with lower ordering temperatures. In particular, long-range magnetic order is observed for a 150 multilayer assembly of the Fe/Ni structure at -8 K, which is lower than the bulk ordering temperature of the three-dimensional material ( 23K). The lower ordering temperature is presumably due to weaker interplane interactions due to the increased separation. 

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Figure 3.19 Formation of two-dimensional magnetic materials using the Langmuir-Blodgett technique. Reprinted with permission from Culp etal., 2005 [57]. Copyright (2005) Elsevier...

Low-dimensional Solids. - 2.10.1 Introduction. The magnetic properties of one and two-dimensional arrays of localized spins coupled by Heisenberg exchange interactions have been studied as a rather specialized branch of theoretical physics since the earliest days of quantum mechanics. However, recent advances in theory, and the preparation of real materials that are a good approximation to the theoretical models, have made low-dimensional systems much more central to condensed-matter science. There is enormous scope for synthetic chemistry in this area and, as will be seen later in this section, many new materials have been discovered recently. 

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