Unusual Critical Behavior of the Diluted Uniaxial Dipolar Ferromagnet LiTb0.3Y0.7F4

Abstract

The experimental critical behavior of the susceptibility of Li${\mathrm{Tb}}_{0.3}$${\mathrm{Y}}_{0.7}$${\mathrm{F}}_{4}$ is described by the power law $\ensuremath{\chi}=\ensuremath{\Gamma}{[\frac{(T\ensuremath{-}{T}_{c})}{{T}_{c}}]}^{\ensuremath{-}\ensuremath{\gamma}}$ with ${T}_{c}=0.520\ifmmode\pm\else\textpm\fi{}0.003$ K and $\ensuremath{\gamma}=1.80\ifmmode\pm\else\textpm\fi{}0.04$. This behavior is dramatically different from that previously observed in LiTb${\mathrm{F}}_{4}$ and is evidence of a departure from marginal dimensionality when magnetic ions have been randomly replaced by nonmagnetic ions. Series expansion of ${(\ensuremath{\chi}T)}^{\ensuremath{-}1}$ in powers of ${T}^{\ensuremath{-}1}$ for a diluted Ising dipolar ferromagnet gives a good description of experimental results described in this Letter.