A muon-spin relaxation (µSR) study of the geometrically frustrated magnets Gd₃Ga₅O₁₂and ZnCr₂O₄

Abstract

We present the results of muon-spin-relaxation experiments for two materials which show geometric frustration. ZnCr 2 O 4 has a spinel structure with S = 3 2 spins on a lattice of corner-sharing tetrahedra. Our experiments show that a local magnetic field which is quasi-static on the muon timescale develops below T c = 12.5 K, a transition which has been associated with a three-dimensional analogue of the spin-Peierls transition. In contrast, Gd 3 Ga 5 O 12 has a garnet structure with S = 7 2 spins arranged on interpenetrating triangular sublattices. In this material the muon data exhibit a temperature-dependent spin-relaxation rate indicative of slow spin fluctuations. We discuss these differing behaviours and relate them to the underlying physics in the two materials.

Low-temperature spin fluctuations in geometrically frustrated Yb3Ga5O12

“…We note that a linear variation has also been encountered theoretically for the case of a frustrated Heisenberg pyrochlore antiferromagnet [5]. The decrease in the relaxation rate followed by a saturation is similar to the behaviour observed (by µSR [13]) in the isomorphous compound Gd 3 Ga 5 O 12 .…”

“…A number of the rare earth garnets appear to evidence a conventional long range ordered state [7] suggesting that in these cases, frustration plays a negligible role. In fact, to date, frustration has been reported to play a major role in only one garnet, Gd 3 Ga 5 O 12 [8][9][10][11][12][13], where the S-state Gd 3+ ion has a very small intrinsic anisotropy and where the dominant coupling is antiferromagnetic.…”

Low-temperature specific heat and possible gap to magnetic excitations in the Heisenberg pyrochlore antiferromagnetGd2Sn2O7

“…Indeed, residual low temperature dynamics has been found in pyrochlore magnetic materials with low temperature states that range from not understood whatsoever 21,29 to seemingly conventional long range ordered 16,17,18,19,20 . We note in passing that persistent low-temperature spin dynamics has also been found in the Gd 3 Ga 5 O 12 garnet (GGG) 30,31 and in the SrCr 8 Ga 4 O 19 kagome antiferromagnet 32 . We now briefly review the various experimentally observed behaviors of the R 2 Ti 2 O 7 and R 2 Sn 2 O 7 pyrochlore oxides.…”

Hidden order in spin-liquid Gd 3 Ga 5 O 12

“…In GGG, a spin-liquid state is observed at temperatures above a spin-glass transition at T g ≈ 0.14 K (13). Evidence for a conventional spin liquid in GGG is the suppression of T g to temperatures far below the antiferromagnetic interaction strength of ∼2 K (14-16), the observation of liquid-like magnetic diffuse scattering in powder neutron-scattering measurements (17), and the persistence of strong spin fluctuations to low temperature (18)(19)(20). Yet, broad anomalies are present in both the non-linear susceptibility χ 3 and the magnetic specific heat at around 0.5 K, which do not yet have a well-understood microscopic origin (13,21).…”