Magnons and fractons in the diluted antiferromagnet Mn/sub x/Zn/sub 1-//sub x/F/sub 2/

Journal Article · Sun Nov 01 04:00:00 EST 1987 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.36.7024· OSTI ID:5797047

Uemura, Y J; Birgeneau, R J

We report high-resolution inelastic-neutron-scattering studies of the spin dynamics in the diluted near-Heisenberg antiferromagnet Mn/sub x/Zn/sub 1-//sub x/F/sub 2/ with x = 0.75 and 0.50. The x = 0.75 experiments reproduce previous results by Coombs et al. (J. Phys. C 9, 2167 (1976)), albeit with much higher resolution. In that case the excitations may be described as spin waves which broaden progressively as the wave vector approaches the zone-boundary value q/sub ZB/. However, even at q/sub ZB/ the excitation is underdamped. More interesting behavior is observed in the x = 0.50 sample. At long wavelengths, the response function S(q,..omega..) is dominated by a sharp spin-wave peak; however, there is a weak ..omega../sup -3/ tail extending to high energies. With increasing wave vector the sharp peak diminishes in intensity while a broad overdamped component, which is well described by a damped-harmonic-oscillator (DHO) function, grows in intensity. The crossover from a dominant spin wave to a dominant DHO response occurs for qapprox.0.3q/sub ZB/. In energy space, this phenomenon manifests itself as a crossover from propagating low-energy spin waves to localized high-energy excitations. An independent measurement of elastic diffuse magnetic scattering from the x = 0.50 sample yields the percolation correlation length xi/sub p/ associated with the dilution as xi/sub p//sup -1/ = 0.3q/sub ZB/. This demonstrates that the crossover in the dynamics occurs at the length scale characteristic of the static geometrical disorder. The results are thence related to the magnon-fracton crossover predicted by recent theories for percolation networks.

• Research Organization: Brookhaven National Laboratory, Upton, New York 11973
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 5797047
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 36:13; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALLOYS
ANTIFERROMAGNETIC MATERIALS
COHERENT SCATTERING
DAMPING
DIFFRACTION
DILUTE ALLOYS
ENERGY LEVELS
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HIGH SPIN STATES
INELASTIC SCATTERING
MAGNETIC MATERIALS
MANGANESE COMPOUNDS
MANGANESE FLUORIDES
MANGANESE HALIDES
MATERIALS
NEUTRON DIFFRACTION
SCATTERING
SPIN WAVES
TRANSITION ELEMENT COMPOUNDS
WAVE PROPAGATION
ZINC COMPOUNDS
ZINC FLUORIDES
ZINC HALIDES