Critical behavior of pure and site-random two-dimensional antiferromagnets

Journal Article · Fri Jul 01 04:00:00 EDT 1977 · Phys. Rev., B; (United States)

DOI:https://doi.org/10.1103/PhysRevB.16.280· OSTI ID:7100551

Birgeneau, R J; Als-Nielsen, J; Shirane, G

Quasielastic neutron-scattering studies of the static critical behavior in the two-dimensional antiferromagnets K/sub 2/NiF/sub 4/, K/sub 2/MnF/sub 4/, and Rb/sub 2/Mn.T/sub 5/Ni/sub 0/./sub 5/ F/sub 4/ are reported. For T < 0.95T/sub N/ the diffuse scattering arises principally from the noncritical transverse susceptibility chi/sup perpendicular/(Q). In all three materials chi/sup perpendicular/(Q) is found to be only weakly temperature dependent for T < T/sub N/ with a halfwidth kappa/sup perpendicular/ consistent with spin-wave theory. For abs. value - T/T/sub N/ < 0.05 the overall scattering is dominated by the critical Ising component chi/sup parallel/(Q). The total scattering is proportional to chi/sup parallel/(Q) + chi/sup perpendicular/(Q) so that, with an appropriate correction for chi/sup perpendicular/(Q), the detailed critical behavior for chi/sup parallel/(Q) may be determined. For the reduced temperature range 0.008 < T/T/sub N/ - 1 < 0.15 one finds in all three materials ..nu.. = 0.9 +- 0.1, ..gamma.. = 1.6 +- 0.15, and from the scaling relation ..gamma.. = ..nu.. (2 - eta), eta = 0.2 +- 0.05. For T < T/sub N/ one finds ..beta.. = 0.15 +- 0.015 in the three systems. Finally, in K/sub 2/NiF/sub 4/ for T < T/sub N/, chi/sup parallel/(0), and kappa/sup parallel/ are consistent with two-dimensional Ising behavior with exponents ..gamma..' = 1.75, ..nu..' = 1; further chi/sup parallel/(+ abs. value epsilon ) approx. = (50 +- 10) chi/sup parallel/(- abs. value epsilon ) compared with the Ising asymmetry factor of 37. These results thus demonstrate that the site-random and pure systems have identical critical behavior in agreement with current theory. Further, the critical behavior is close to that of the two-dimensional Ising model, although there are small differences, assumedly due to the fact that the experiments do not probe the true asymptotic region. Finally a number of inconsistencies in earlier experiments are resolved.

• Research Organization: Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
• OSTI ID: 7100551
• Journal Information: Phys. Rev., B; (United States), Journal Name: Phys. Rev., B; (United States) Vol. 16:1; ISSN PLRBA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALKALI METAL COMPOUNDS
ANTIFERROMAGNETISM
COHERENT SCATTERING
CRITICAL TEMPERATURE
CRYSTAL MODELS
DIFFRACTION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
ISING MODEL
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MAGNETISM
MANGANESE COMPOUNDS
MANGANESE FLUORIDES
MANGANESE HALIDES
MATHEMATICAL MODELS
NEUTRON DIFFRACTION
NICKEL COMPOUNDS
NICKEL FLUORIDES
PHYSICAL PROPERTIES
POTASSIUM COMPOUNDS
POTASSIUM FLUORIDES
RUBIDIUM COMPOUNDS
RUBIDIUM FLUORIDES
SCATTERING
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE