Subhajit Sarkar, Samir K. Paul, Ranjan Chaudhury
A theoretical study has been carried out to analyse the available results from the inelastic neutron scattering experiments performed on quasi-two dimensional ferromagnets. The formalism is based on a conventional semi-classical like treatment involving a model of an ideal gas of vortices/anti-vortices corresponding to an XY-anisotropic Heisenberg ferromagnet on a square lattice. The above analysis, when applied to a layered ferromagnet K_2Cu F_4, yields negative values of dynamical structure functions for a large range of energy transfer. This indicates a complete breakdown of the conventional theoretical framework and strongly suggests the necessity for developing a full quantum formalism to calculate dynamical spin- spin correlation for a layered spin 1/2 ferromagnet. This investigation is expected to throw a new light on the characterization of quantum topological excitations.
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http://arxiv.org/abs/1203.3069
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