Physics

Prof. Varsha Banerji
IIT, Delhi

Many magnetic and dielectric solids are well-represented by (i) the random field Ising model with conserved order parameter (C-RFIM) and (ii) the Ising model with dipolar interactions (IM+DI). We perform deep quenches to study the kinetics of domain growth in these spin systems. In the C-RFIM, (a) the correlation function exhibits dynamical scaling but is not robust with respect to the disorder ∆; (b) at early times the domains follow algebraic growth with a disorderdependent exponent: L(t, ∆) ∼ t 1/z(∆). At late times, there is a cross-over to logarithmic growth L(t, ∆) ∼ (ln t) 1/ϕ, where ϕ is the disorder-independent logarithmic exponent. In the IM+DI, (a) there is emergence of columnar domains along z-axis (Ising axis) with a transient periodicity in the xy-plane; (b) there are anisotropic growth laws: `ρ(t) ∼ t φ ; `z(t) ∼ t ψ, where ~ρ = (x, y) and ` is the characteristic length scale. Our results explain experimental observations in a wide range of complex systems and have important technological implications.