Spin freezing in the spin-liquid compound FeAl2O4

Spin freezing in the A-site spinel FeAl2O4, which is a spin-liquid candidate, is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl2O4 differs significantly from that of a canonical spin glass, which is also supported by analysis of the nonlinear magnetic susceptibility term chi(3)(T). Through the power-law analysis of chi(3)(T), a spin-freezing temperature T-g = 11.4 +/- 0.9 K and critical exponent gamma = 1.48 +/- 0.59 are obtained. A Cole-Cole analysis of magnetic susceptibility shows the presence of broad spin relaxation times in FeAl2O4, however, the irreversible dc susceptibility plot discourages an interpretation based on conventional spin-glass features. The magnetization measured using the cooling-and-heating-in-unequal-fields protocol brings more insight into the magnetic nature of this frustrated magnet and reveals unconventional glassy behavior. Combining our results, we arrive at the conclusion that the present sample of FeAl2O4 consists of a majority spin-liquid phase with "glassy" regions embedded.