Random-field effects on the order in the diluted weakly anisotropic antiferromagnetK2NixZn1−xF4

Abstract

With the use of neutron diffraction, the effects of random fields are studied in the diluted quadratic-layer antiferromagnet ${\mathrm{K}}_{2}{\mathrm{Ni}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{F}}_{4}$ for $x=0.96, 0.85, \mathrm{and} 0.75$. Upon cooling in external fields as small as $H\ensuremath{\sim}0.1$ T, the systems quench into a nonequilibrium domain state characterized by the absence of long-range order along the $c$ axis. At low Zn concentrations and low fields the interplane inverse correlation length follows ${\ensuremath{\kappa}}_{z}\ensuremath{\propto} {H}^{0.71\ifmmode\pm\else\textpm\fi{}0.03}$. The order within the planes is also affected, but remains unexpectedly long ranged.