Random Field Models for Relaxor Ferroelectric Behavior

Abstract

Heat bath Monte Carlo simulations have been used to study a four-state clock model with a type of random field on simple cubic lattices. The model has the standard nonrandom two-spin exchange term with coupling energy $J$ and a random field which consists of adding an energy $D$ to one of the four spin states, chosen randomly at each site. This Ashkin-Teller-like model does not separate; the two random-field Ising model components are coupled. When $D/J=3$, the ground states of the model remain fully aligned. When $D/J\ge 4$, a different type of ground state is found, in which the occupation of two of the four spin states is close to 50%, and the other two are nearly absent. This means that one of the Ising components is almost completely ordered, while the other one has only short-range correlations. A large peak in the structure factor $S(k)$ appears at small $k$ for temperatures well above the transition to long-range order, and the appearance of this peak is associated with slow, "glassy" dynamics. The phase transition into the state where one Ising component is long-range ordered appears to be first order, but the latent heat is very small.

7 pages + 12 eps figures, to appear in Phys Rev B

References in corpus (1)

• Order Parameter Criticality of the d=3 Random-Field Ising Antiferromagnet Fe(0.85)Zn(0.15)F2

Cited by in corpus (18)

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• Direct Imaging of Temperature Evolution of Polar Nanoregions and Chemically Ordered Regions in PMN Relaxor: Evidence for Polar Phase Percolation
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