Dynamical properties of a crystalline rare-earth boron cluster spin-glass system

Dynamical properties of the magnetic B₁₂ cluster compound HoB₂₂C₂N were investigated. HoB₂₂C₂N is taken to be representative of the class of trigonal and rhombohedral B₁₂ cluster compounds which were found to exhibit spin-glass behavior as measured by dc superconducting quantum interference device magnetometer and specific-heat measurements. These are examples of magnetic glassiness being observed in rare earth boron-rich crystalline cluster compounds. Well defined maxima in the in-phase linear ac susceptibility χ^' curves were observed, indicative of the spin-glass transition. Strong frequency dependence of the cusp temperature Tf was found. The dependence of Tf could not be analyzed satisfactorily by the dynamical scaling theory of a three-dimensional spin glass. A more detailed investigation of the behavior of relaxation times by Cole-Cole analysis showed that the behavior in HoB₂₂C₂N is different from the simple blocking of a superparamagnetic system, because of the temperature dependence of the parameter α representing the width of the relaxation-time distribution function g(τ). The median relaxation time was also determined and the data were found to be described well in terms of a generalized Arrhenius law lnτ∝T^-2.5. These results indicate that HoB₂₂C₂N is a two-dimensional spin-glass system, which supports what has been speculated previously.