Critical Magnetic Scattering in Manganese Fluoride

Abstract

The angular dependence of the quasielastic magnetic scattering has been measured in Mn${\mathrm{F}}_{2}$ in the critical region $T>{T}_{N}$. The temperature dependence of the inverse correlation range and the staggered mode susceptibility for both transverse and longitudinal spin fluctuations were observed as a function of incident neutron energy over the range $56<{E}_{0}<134$ meV. The validity of the quasielastic approximation for this energy region was verified. The data for the longitudinal fluctuations were found to follow simple power laws with the critical exponents $\ensuremath{\nu}=0.634\ifmmode\pm\else\textpm\fi{}0.02$, $\ensuremath{\gamma}=1.24\ifmmode\pm\else\textpm\fi{}0.02$. An $\ensuremath{\eta}$ fitted to the data closest to ${T}_{N}$ gave $\ensuremath{\eta}=0.05\ifmmode\pm\else\textpm\fi{}0.02$. The transverse fluctuations are not divergent at ${T}_{N}$, although for $T>{T}_{N}$ they can be described by power-law fits taken with respect to a temperature ${T}_{\ensuremath{\perp}}\ensuremath{\approx}66\ifmmode^\circ\else\textdegree\fi{}$K by indices ${\ensuremath{\nu}}_{\ensuremath{\perp}}=0.63\ifmmode\pm\else\textpm\fi{}0.08$, ${\ensuremath{\gamma}}_{\ensuremath{\perp}}=1.47\ifmmode\pm\else\textpm\fi{}0.1$. The actual critical temperature is ${T}_{N}=67.458\ifmmode\pm\else\textpm\fi{}0.008$.