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arXiv · 1904.00909

51V-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8

H. Takeda·H. Yasuoka·M. Yoshida·M. Takigawa·N. J. Ghimire·D. Mandrus·B. C. Sales
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Abstract

Static and dynamic properties of the quasi-two-dimensional antiferromagnet K$_2$V$_3$O$_8$ have been investigated by $^{51}$V-NMR experiments on nonmagnetic V$^{5+}$ sites. Above the structural transition temperature $T_{\rm{S}}$ = 115 K, NMR spectra are fully compatible with the $P4bm$ space group symmetry. The formation of superstructure below $T_{\rm{S}}$ causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along $c$-axis below the magnetic transition temperature $T_{\rm{N}} \sim 4$ K is qualitatively consistent with a simple Néel order and a spin flop transition. However, broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate $1/T_1$ below $T_{\rm{N}}$ shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V$^{5+}$ and magnetic V$^{4+}$ sites. The results indicate strong gapless spin fluctuations, which could arise from incommesurate orders or complex spin textures.

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H. Takeda, H. Yasuoka, M. Yoshida, M. Takigawa, N. J. Ghimire, D. Mandrus, B. C. Sales. 2019-04-01. 51V-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8. https://doi.org/10.1103/physrevb.100.054406

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