Critical fluctuations in the 2D XY antiferromagnet BaNi2(PO4)2 : NMR measurements
Non-linear excitations are known to play a crucial role in low-dimensional magnetism. For the two-dimensional (2D) XY model these non-linear excitations are described in terms of vortices which govern the so-called Kosterlitz-Thouless transition occuring at a temperature TKT>0. We present here results of 31P nuclear magnetic resonance obtained on the compound BaNi2(PO4)2 which is a good example of a quasi 2D XY type antiferromagnet. Above the 3D magnetic ordering occuring at a temperature TN ≈- 23.6 K a diverging behaviour is observed for the corresponding nuclear spin-lattice relaxation (NSLR) rate 1/T1. We show that this behaviour can be interpreted in the recent model of Mertens et al. describing the dynamical behaviour of free vortices.
KeywordsFree Vortex Fluctuation Spectrum Real Magnetic System Frequency Fluctuation Spectrum Magnetic Fluctuation Spectrum
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