Observation of Successive Phase Transitions in Kagome Lattice Antiferromagnets RFe_3(OH)_6(SO_4)_2「R=NH_4,Na,K]

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Successive magnetic phase transitions were found in the Kagom! lattice antiferromagnetsRFe3(OH)5(SO,j)z [R : NH,j,Na,K]. The temperature dependence of the susceptibility has twocusps around 60 K for each compound. The X-ray diffraction patterns and the quadrupole reso-nance spectra show that the transitions are not caused by a strtrctural change. The presence ofthese transitions was confirmed by NKIR experiments. The NMR spectra show the developmentof magnetic ordering below the upper transition temperature. In the low-temperatture phase thenuclear magnetization does not relax exponentially, which may suggest a dounain structure of120' spin strttcture due to degeneracy on the Kagom! lattice. The successive transitions may becaused by a srnall Ising-like anisotropy in the Heisenberg antiferromagnet.
社団法人日本物理学会の論文
1996-09-15