Magnetic ordering and spin dynamics in potassium jarosite: A Heisenberg kagomé lattice antiferromagnet

Abstract

The spin dynamics of the Heisenberg kagomé lattice antiferromagnet, potassium jarosite KFe 3 (OH) 6 (SO 4 ) 2 , have been investigated by means of NMR. The NMR spectra confirm the long-range magnetic ordering below 65 K and the qϭ0 type 120°spin structure with positive chirality in the ordered phase. Though the Heisenberg kagomé lattice antiferromagnet is considered theoretically to remain disordered down to zero temperature due to the continuous degeneracy of the ground state, the long-range magnetic ordering at the finite temperature is realized in this compound due to the weak anisotropy. The spin-lattice relaxation rate, 1/T 1 , in the ordered phase decreases sharply with lowering temperature. The experimental rate is well explained by the twomagnon process of the spin waves having an energy gap of 15 K. The temperature dependence of the sublattice magnetization also supports the existence of the spin wave. These are the first experimental evidence that the low-energy excitation in the frustrated classical kagomé lattice antiferromagnet is described by the spin wave. We calculate the spin wave in the qϭ0 type 120°spin structure with weak single-ion-type anisotropy, and discuss the characteristics of the spin fluctuations in the Heisenberg kagomé lattice antiferromagnet.

Magnetic structure and spin waves in the Kagomé jarosite compoundKFe3(SO4)2(Yildirim1, Harris2 2006Phys. Rev. B650320View full textAdd to dashboardCite

“…In recent years, it has been shown that the jarosite family of miner-als AM 3 (OH) 6 (SO 4 ) 2 , 13,14,15,16,17,18,19,20,21 (where A is monovalent ion such as K + , and M is trivalent cation such as Fe 3+ , Cr 3+ , or V 3+ ) form much better realization of the two dimensional (2D) Kagomé lattice. As shown in Fig.…”

“…Inami et al 14,16 have pointed out that in FeJ, the oxygen-octahedra are significantly tilted (see Fig. 2), thereby inducing a strong single-ion crystal field (CF) anisotropy.…”

“…The effect of D y is also to cant the spins (so that they have a small outof-plane component) into the observed "umbrella" spin configuration. Finally, since the DM interaction occurs at first-order in the spin-orbit coupling, it is expected to be larger than the CF terms of Inami et al 14,16 In order to identify the origin of the magnetic interactions that are responsible for the LRO in FeJ compounds, clearly we need more experimental data such as the observed spin-wave spectrum. Fortunately, thanks to the very recent progress in the synthesis of high-quality single crystals of FeJ compounds, 19,21 such spin-wave data has been recently become available.…”

“…9 and the single-ion anisotropy terms are those used by Nishiyama et al 16 in their treatment of the spin-wave spectrum in jarosites. Here the prime-spin components refer to the local axis associated with the rotated oxygen octahedra shown in Fig.…”

Determination of the single-ion anisotropy energy in aS=52kagome antiferromagnet using x-ray absorption spectroscopy

“…In this system a transition to a noncollinear long-range-ordered state is observed at 64 K despite that the magnitude of the Curie-Weiss temperature ⌰ CW is as high as −800 K. 11,17 The ground state has shown to be a so-called q = 0 state of positive chirality, in which the spins lie within the kagome plane and all point either in or out of each shared kagome triangle. 9,12,13,18,19 The large figure ⌰ CW / T N = 12.5 is an indication of relatively strong geometric frustration, 20 but clearly the observed longrange-ordered ground state points to additional terms in the Hamiltonian of this kagome antiferromagnet beyond nearneighbor exchange. It has been shown that the q = 0 ground state can arise due to magnetic anisotropies such as easyplane single-ion crystal-field ͑CF͒ anisotropy D z Ŝ z 2 − E xy ͑Ŝ x 2 − Ŝ y 2 ͒, 21,22 where D z is the zero-field splitting parameter, or a Dzyaloshinsky-Moriya interaction ͑DMI͒ ͑Refs.…”