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Title: Phonon-assisted relaxation in a frustrated antiferromagnet

Abstract

A thermally activated magnetic relaxation is observed using neutron spin-echo in the pyrochlore slab (kagom{acute e} bilayer) compound SrCr{sub 9x}Ga{sub 12-9x}O{sub 19} (x=0.95) in a restricted temperature range, 4K < T < 4K, above a cross-over to a low temperature relaxation regime with a weaker temperature dependence. The activation energy of the thermally activated relaxation, of the order of 7 meV, coincides with the energy of a phonon mode observed with neutron and Raman spectroscopy, indicating a phonon-assisted regime. The experimental observation of phonon-assisted process gives additional insight to the importance of spin-phonon coupling in frustrated magnets with regard to the models mostly based on purely magnetic interactions.

Authors:
 [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931324
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: ICM 2006, Kyoto, Japan, 20060820, 20060820
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACTIVATION ENERGY; MAGNETS; NEUTRONS; PHONONS; PYROCHLORE; RAMAN SPECTROSCOPY; RELAXATION; SPIN ECHO; TEMPERATURE DEPENDENCE

Citation Formats

Ehlers, Georg. Phonon-assisted relaxation in a frustrated antiferromagnet. United States: N. p., 2006. Web.
Ehlers, Georg. Phonon-assisted relaxation in a frustrated antiferromagnet. United States.
Ehlers, Georg. 2006. "Phonon-assisted relaxation in a frustrated antiferromagnet". United States. doi:.
@article{osti_931324,
title = {Phonon-assisted relaxation in a frustrated antiferromagnet},
author = {Ehlers, Georg},
abstractNote = {A thermally activated magnetic relaxation is observed using neutron spin-echo in the pyrochlore slab (kagom{acute e} bilayer) compound SrCr{sub 9x}Ga{sub 12-9x}O{sub 19} (x=0.95) in a restricted temperature range, 4K < T < 4K, above a cross-over to a low temperature relaxation regime with a weaker temperature dependence. The activation energy of the thermally activated relaxation, of the order of 7 meV, coincides with the energy of a phonon mode observed with neutron and Raman spectroscopy, indicating a phonon-assisted regime. The experimental observation of phonon-assisted process gives additional insight to the importance of spin-phonon coupling in frustrated magnets with regard to the models mostly based on purely magnetic interactions.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2006,
month = 1
}

Conference:
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  • A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagome bilayer compounds SrCr{sub 9x}Ga{sub 12-9x}O{sub 19} (x = 0.95, SCGO) and Ba{sub 2}Sn{sub 2}ZnCr{sub 7x}Ga{sub 10-7x}O{sub 22} (x = 0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at T{sub g}, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K ({approx} T{sub g}) < T < 7 K, the relaxation rate activation energy E{sub a} = 7 {+-} 0.4 meV, equal to the energy of a phonon mode, pointing out the rolemore » of spin-lattice coupling.« less
  • A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagome bilayer compounds SrCr{sub 9x}Ga{sub 12-9x}O{sub 19} (x=0.95, SCGO) and Ba{sub 2}Sn{sub 2}ZnCr{sub 7x}Ga{sub 10-7x}O{sub 22} (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at T{sub g}, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K ({approx_equal}T{sub g})<T<7 K, the relaxation rate activation energy E{sub a}=7{+-}0.4 meV, equal to the energy of a phonon mode, pointing out the role of spin-lattice coupling.
  • In this study, PbCuTe 2O 6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu 2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointingmore » to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T 1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less
  • The purpose of the present report is to study: (1) Relaxation from an initially random flux state. We wish to exhibit the multiple length and time scales involved in this relaxation, and the influence of thermal fluctuations. This noisy relaxation is controlled by the dynamics of various mesoscopic defect'' structures defined with respect to the underlying ground-state flux structure. The defects, their mesoscopic collective patterns, and their dynamics control a complex macroscopic response, but are themselves microscopically controlled by the competitions producing the ground-state flux completely. Such multiscaleresponses have been observed in other competing interaction systems e.g., spin glasses, randommore » field magnets, and weakly pinned charge-density waves, as well as noisy responses in high-temperature superconductors. Various creep'' and stretched-exponential'' regimes have been proposed, as well as phenomenological scaling theories attempting to relate spatial domain sizes with temporal scales. (2) Noisy (i.e.,multitime-scale) voltages responses, and their relation to multilength scales, in current driven JJA's in the presence of a uniform extended magnetic field which frustrates the flux order.« less