DOMAIN GROWTH IN THE 3-DIMENSIONAL RANDOM-FIELD ISING MAGNET FE0.5ZN0.5F2

Complementary neutron-scattering and superconducting quantum interference device (SQUID) magnetometry measurements have been carried out to study the time dependence of the field-cooled metastable domains in Fe0.5Zn0.5F2. These neutron-scattering data provide direct evidence of a logarithmic increase in the correlation length upon quenching the system to T≤Tc at H=5.5 T. At low temperatures the magnetic domains are frozen on experimental time scales. SQUID measurements performed at a series of fields and temperatures confirm the evolution of the excess magnetization Mex arising from domain surfaces and allow quantitative analysis of its time dependence. Specifically, we found that Mex∼HMν[ln(t/τ)]-ψ, where νM=2.7±0.1 and ψ=1.1±0.3 for H3.45 T; ψ is much less than 1 for lower fields. In particular, ψ=0.42±0.14 at H=1.5 T, in agreement with a prediction by Nattermann and Vilfan. At H=5.5 T, Mex(T) and the inverse correlation length κ(T) exhibit identical time dependences. Overall, these measurements reveal the varied time dependence of a field-cooled, strongly anisotropic dilute antiferromagnet in different applied fields, and shed light on the mechanisms of domain evolution. © 1995 The American Physical Society.