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arXiv · 2112.02616

${}^{31}$P NMR investigation of quasi-two-dimensional magnetic correlations in $T_2$P$_2$S$_6$ ($T$ = Mn & Ni)

F. Bougamha·S. Selter·Y. Shemerliuk·S. Aswartham·A. Benali·B. Büchner·H. -J. Grafe·A. P. Dioguardi
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Abstract

We report the anomalous breakdown in the scaling of the microscopic magnetic susceptibility, as measured via the ${}^{31}$P nuclear magnetic resonance (NMR) shift $K$, with the bulk magnetic susceptibility $\chi$ in the paramagnetic state of Mn$_2$P$_2$S$_6$. This anomaly occurs near $T_\mathrm{max} \sim 117$ K the maximum in $\chi(T)$ and is therefore associated with the onset of quasi-two-dimensional (quasi-2D) magnetic correlations. The spin-lattice relaxation rate divided by temperature $(T_1T)^{-1}$ in Mn$_2$P$_2$S$_6$ exhibits broad peak-like behavior as a function of temperature, qualitatively following $\chi$, but displaying no evidence of critical slowing down above the N\'{e}el temperature $T_N$. In the magnetic state of Mn$_2$P$_2$S$_6$, NMR spectra provide good evidence for 60 degree rotation of stacking-fault-induced magnetic domains, as well as observation of the spin-flop transition that onsets at 4 T. The temperature-dependent critical behavior of the internal hyperfine field at the P site in Mn$_2$P$_2$S$_6$ is consistent with previous measurements and the two-dimensional anisotropic Heisenberg model. In a sample of Ni$_2$P$_2$S$_6$, we observe only two magnetically split resonances in the magnetic state, demonstrating that the multiple-peaked NMR spectra previously associated with 60 degree rotation of stacking faults is sample dependent. Finally, we report the observation of a spin-flop-induced splitting of the NMR spectra in Ni$_2$P$_2$S$_6$, with an onset spin-flop field of $H_\mathrm{sf} = 14$ T.

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F. Bougamha, S. Selter, Y. Shemerliuk, S. Aswartham, A. Benali, B. Büchner, H. -J. Grafe, A. P. Dioguardi. 2021-12-05. ${}^{31}$P NMR investigation of quasi-two-dimensional magnetic correlations in $T_2$P$_2$S$_6$ ($T$ = Mn & Ni). https://doi.org/10.1103/physrevb.105.024410

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