The Magnetic Behaviors of Spin-Glass $hbox{FeGa}_{2}hbox{O}_{4}$ System

摘要

We present the investigation of magnetic properties of spin-glass ${rm FeGa}_{2}{rm O}_{4}$ system. From X-ray diffraction patterns of ${rm FeGa}_{2}{rm O}_{4}$, refined with Rietveld''s refinement method, its structure is determined to be cubic spinel with space group $Fd-3m$ and the lattice parameter of $a_{0}=8.385 hbox{rm{AA}}$. From temperature-dependent magnetization curves under 1000 Oe, the Néel temperature is found to be $T_{rm N}=14 {rm K}$ , which coincides with the value obtained from the Mössbauer spectrum. The freezing temperature $T_{rm f}$ of the sample shifts to higher temperature with increasing frequency, as seen in conventional metallic spin glasses. Also, we have determined the small activation energy, $E_{rm a}$ of $1.04266times 10^{-4} {rm meV}$ from Arrhenius law $nu=nu_{0}exp(-E_{rm a}/k_{rm B}T_{rm f})$ , where $k_{rm B}$ is Boltzmann constant, and $E_{rm a}$ is activation energy. The Mössbauer spectrum at 4.2 K shows severely distorted 8-line shape coming from frozen spin-disorder state and an incommensurate spin structure, as in spin glasses. The change in the electric quadrupole shift above $T_{rm f}$ is c-nused by the presence of the maximum electric dipole interaction among frozen disordered spins around $T_{rm f}$ as in spin-glass material, and charge re-distribution from spin-relocation arising above $T_{rm N}$ .