We report magnetic properties in the random spinel magnet ${\mathrm{CoGa}}_2{\mathrm{O}}_4$. Rietveld analysis of the x-ray diffraction profile for ${\mathrm{CoGa}}_2{\mathrm{O}}_4$ reveals that the Co and Ga ions are distributed randomly in the tetrahedral $A$ sites and octahedral $B$ sites in the cubic spinel structure. ${\mathrm{CoGa}}_2{\mathrm{O}}_4$ exhibits a spin-glass transition at $T_{\mathrm{SG}}=8.2\mathrm{K}$ that is confirmed by measurements of the dc and ac susceptibilities and thermoremanent magnetization (TRM) that develops below $T_{\mathrm{SG}}$. From the frequency dependence of the freezing temperature $T_{\mathrm{f}}$ for ${\mathrm{CoGa}}_2{\mathrm{O}}_4$, it is indicated that the relaxation time $\tau \left(T\right)$ follows a Vogel-Fulcher law $\tau ={\tau }_0\exp [-E_a/k_{\mathrm{B}}(T-T_0\left)\right]$. An analysis of specific heat suggested that a doublet ground state of the octahedrally coordinated ${\mathrm{Co}}^{2+}$ was stabilized by spin-orbit and crystal field couplings. The relaxation rate of TRM is considerably enhanced at $T_{\mathrm{SG}}$ and decays rapidly above and below $T_{\mathrm{SG}}$. The time course of TRM is reproduced by nonexponential relaxation forms, such as a stretched exponential (Kohlrausch) as well as Ogielski and Weron relaxation forms. This behavior is displayed universally in glass systems, and the characteristic parameters associated with these functions were reasonable.

• Received 28 October 2020
• Accepted 25 May 2021
• Corrected 18 February 2022

DOI:https://doi.org/10.1103/PhysRevB.103.224408