Phase-transition behavior in the random-field antiferromagnet Fe{sub 0.5}Zn{sub 0.5}F{sub 2}
- Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
- ATT Bell Laboratories, 600 Mountain Avenue, Murray Hill, New Jersey 07974 (United States)
- Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
We present a combined magnetic x-ray and neutron scattering study of the order parameter of the diluted antiferromagnet Fe{sub 0.5}Zn{sub 0.5}F{sub 2} in an applied field. This system is believed to be modeled by the three-dimensional random-field Ising model. A long range ordered (LRO) state is prepared through a zero-field-cooled procedure (ZFC). The evolution of this LRO state is studied on warming at fixed field. The x-ray order parameter data are well described by a power-law-like transition at all fields with an exponent {beta}{sub ZFC} varying from 0.21 to 0.12. The transition region is broadened and may be described by a Gaussian distribution of transition temperatures, centered at T{sub C}(H), of width {sigma}{sub ZFC}(H). It is found that {sigma}{sub ZFC}(H)=AH{sup 2}+B. This rounding is attributed to anomalously slow dynamics, which prevents equilibrium being attained for experimentally relevant time scales for T{lt}T{sub M}(H) where T{sub M}(H) is the temperature below which metastability effects occur. The apparent critical behavior in fact represents a continuous evolution from metastable behavior towards equilibrium behavior. Neutron scattering studies on the same sample allow identification of T{sub C}(H) with the temperature at which the correlation length of the zero-field-cooled fluctuations reaches a maximum value, equal to the corresponding field-cooled value. A qualitative finite size scaling argument is presented to explain the H{sup 2} width dependence. Data showing similar scaling of the width of the ZFC transition region inferred from the temperature derivative of the uniform magnetization as measured by SQUID magnetometry and from neutron scattering measurements of the pseudocritical scattering are also presented. These results lead to an interpretation of indirect specific heat measurements in which the ZFC peak structure is seen to arise entirely from a LRO contribution to the measured quantity. (Abstract Truncated)
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 459839
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 55, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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