Phase transitions and slow spin dynamics of slightly inverted A-site spinel CoAlGaO.

We report the properties of an A-site spinel magnet, CoAlGaO, and analyze its anomalous, low-temperature magnetic behavior, which is derived from inherent, magnetically frustrated interactions. Rietveld analysis of the x-ray diffraction profile for CoAlGaOrevealed that the metallic ions were randomly distributed in the tetrahedral (A-) and octahedral (B-) sites in the cubic spinel structure. The inversion parametercould be controlled by varying the gallium (Ga) composition in the range 0.055 ⩽⩽ 0.664. The composition-induced Néel-to-spin-glass (NSG) transition occurred between 0.05 ⩽⩽ 0.08 and was verified by measurements of DC-AC susceptibilitiesand thermoremanent magnetization (TRM) below the Néel transition temperature. The relaxation rate and derivative with respect to temperature of TRM increased at bothand the spin glass (SG) transition temperature. The TRM decayed rapidly above and below these transitions. TRM was highly sensitive to macroscopic magnetic transitions that occurred in both the Néel and SG phases of CoAlGaO. In the vicinity of the NSG boundary, there was a maximum of the TRM relaxation rate at<. With increasing inversion(), the anomaly atmerged with that of the Néel transition at a tricritical point (,) = (0.08, 4.0 K), where the paramagnetic, Néel, and SG states met. We successfully extracted the relaxation timeand other characteristic parameters from the TRM isothermal temporal evolution based on the Weron function derived for a purely stochastic process. To distinguish the magnetic states, we compared our results with previously studied inversion-free A-site spinel, CoRhO, and CoGaOcluster glass. We generated an inversion-temperature phase diagram based on the comprehensive measurements of DC and AC susceptibilities, TRM, and specific heat in the range 0.055 ⩽⩽ 0.664 for CoAlGaO. Based on this phase diagram, we speculate that a NSG quantum critical phase transition occurred at= 0.050(6). Our findings are consistent with suppression of the long-range order antiferromagnetic state in CoAlOrevealed through neutron diffraction studies, even at<<.