Neutron Spin-Echo Investigation of Slow Spin Dynamics in Kagomé-Bilayer Frustrated Magnets as Evidence for Phonon Assisted Relaxation inSrCr9xGa12−9xO19

Abstract

A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagomé bilayer compounds SrCr9xGa12-9xO19 (x=0.95, SCGO) and Ba2Sn2ZnCr7xGa10-7xO22 (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at Tg, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K (approximately Tg)<T<7 K, the relaxation rate activation energy Ea=7+/-0.4 meV, equal to the energy of a phonon mode, pointing out the role of spin-lattice coupling.

Scaling behaviour of magnetic transitions in Ni3V2O8

“…It remains controversial whether the ground state for Heisenberg spins is ordered magnetically [4], but it is widely accepted that the magnetic structure in these Kagome materials should be extremely sensitive to small interlayer couplings, quantum fluctuations, and anisotropy [5]. Experimentally, a number of behaviours are observed in Kagome lattices, including spin-glass features in SrCr 9x Ga 12À9x O 19 [6]. Recently, Ni 3 V 2 O 8 , has emerged as another experimental system for investigating magnetic ordering transitions on the Kagome lattice.…”

Spin dynamics, short-range order, and spin freezing inY0.5Ca0.5Ba

“…Topical materials in this class include S = 1/2 systems such as volborthite, Cu 3 V 2 O 7 (OH) 2 · 2H 2 O, [3][4][5] and herbertsmithite, ZnCu 3 (OH) 6 Cl 2 , 6-10 as well as others with a higher spin quantum number, such as the S = 5/2 jarosites AFe 3 (OH) 6 (SO 4 ) 2 , 11,12 and the double kagome layer (termed pyrochlore slab) compounds with S = 3/2-SrCr 9x Ga 12−9x O 19 (SCGO) (Refs. [13][14][15][16][17] and Ba 2 Sn 2 ZnCr 7x Ga 10−7x O 22 (BSZCGO). [18][19][20][21] Owing to a complicated chemical composition and crystal structure, the low-temperature properties of these systems are complex and sometimes controversial.…”

Phonon-assisted relaxation in a frustrated antiferromagnet

“…The puzzling properties of this compound were found in the late 1980s and since then it has been extensively studied as a representative example of strongly frustrated antiferromagnets. The present findings are based on neutron spinecho observation of the magnetic relaxation in the temperature range where a spin-glass-like freezing is evident in bulk susceptibility measurements and additional measurements on phonon response using neutron and Raman spectroscopy [3].The static bulk susceptibility of SrCr 9x Ga 12À9x O 19 ðxo1Þ obeys a Curie-Weiss trend in a broad range of temperature reaching well below the mean-field energy scale given by the Curie-Weiss temperature y CW % À400 K, see for example Refs. [1,6].…”

“…The puzzling properties of this compound were found in the late 1980s and since then it has been extensively studied as a representative example of strongly frustrated antiferromagnets. The present findings are based on neutron spinecho observation of the magnetic relaxation in the temperature range where a spin-glass-like freezing is evident in bulk susceptibility measurements and additional measurements on phonon response using neutron and Raman spectroscopy [3].…”

“…More recently an improved version of the NSE instrument, IN11C with enhanced detector solid angle, has become available at the Institut Laue Langevin. Taking advantage of this improvement we obtained new results on the temperature dependence of the intermediate scattering function sðtÞ, measured on a powder sample over the Q-range corresponding to the short-range correlations of the magnetic moments [3]. The temperature dependence of the magnetic relaxation time tðTÞ was obtained from the NSE data by fitting with a stretched exponential line-shape that represents an adequate phenomenological model for the time decay of the intermediate scattering function.…”