Low-temperature phase transitions and collective excitations in a singlet magnet

Green’s function diagrammatic technique is used to study phase transitions in a singlet ferromagnet (S = 1) over a wide range of values of transverse magnetic field and temperature. The T–H and T–D phase diagrams are constructed in the first order with respect to the reciprocal effective radius of interaction. Theoretical and experimental T–H phase diagrams are compared for the NiSiF6·6H2O singlet magnet. It is shown that fluctuations may result in a considerable renormalization of the phase transition temperature. The spectrum and damping of collective excitations in the paramagnetic phase of a low-temperature magnet are discussed.

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