Dzyaloshinsky-Moriya interaction and the ground state in S=3/2 perfect kagome lattice antiferromagnet $\mathbf{KCr_3(OH)_6(SO_4)_2}$ (Cr-jarosite) studied by X-band and high-frequency ESR

摘要

A single crystal S=3/2 perfect kagome lattice antiferromagnet$\mathrm{KCr_3(OH)_6(SO_4)_2}$ (Cr-jarosite) has been studied by X-band andhigh-frequency electron spin resonance (ESR). The g-values perpendicular to thekagome plane (c-axis) and in the plane are determined to be $g_c=1.9704 \pm0.0002$ and $g_\xi=1.9720 \pm 0.0003$, respectively, by high-frequency ESRobserved at 265 K. Antiferromagnetic resonances (AFMR) with theantiferromagnetic gap of 120 GHz are observed at 1.9 K, which is below$T_N$=4.5 K. The analysis of AFMR modes by the conventional molecular fieldtheory shows $d_p=0.27$ K and $d_z=0.07$ K, where $d_p$ and $d_z$ are in-planeand out-of-plane components of DM d vector, respectively. From these resultsand the estimated exchange interaction J=6.15 K by Okuta et al., the groundstate of Cr-jarosite is discussed in connection with the Monte Carlosimulations result with classical Heisenberg spins on the kagome lattice byElhajal et al. Finally, the angular dependence of linewidth and the lineshapeobserved at 296 K by X-band ESR show typical behavior of a two-dimensionalHeisenberg antiferromagnet, suggesting a good two-dimensionality ofCr-jarosite.