ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Using "naive mean-field theory,'' we first consider a square lattice of XY spins with nearest-neighbor ferromagnetic interactions, except for one "frustrated'' (Fr) spin with two antiferromagnetic bonds. At T=0 the Fr spin points perpendicularly to the more distant spins, with its four nearest neighbors tipping slightly towards it (or away from it) according to whether the bonds are ferromagnetic or antiferromagnetic. In this case the mean field on the Fr spin is much less than on the more distant spins, so that it is not surprising that the Fr spin loses its magnetism at a lower temperature than the spins of the ferromagnetic matrix. As the Fr spin "melts,'' the rest of the spins become more collinear. Thus the net magnetization is subject to a competition between the length decrease of the ferromagnetic spins, and their increased collinearity, as T is raised. We next consider the case where many such Fr spins are embedded in the ferromagnetic matrix. For a given value of the antiferromagnetic exchange, it is not difficult to find concentrations of Fr spins whose mean-field solutions yield magnetizations which are low at low T, which begin to rise near Tc (leading to a plateaulike shape), and which disappear above Tc. This behavior is in qualitative correspondence with what is observed in the reentrant state.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.335058
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