Competing effect of blocking and spin frustration in nanostructured gadolinium iron garnets

The ground state magnetic properties and relaxation mechanism in magnetically frustrated system of Gd$_{3}$Fe$_{5}$O$_{12}$ is of topical interest due to its complex magnetic structure. As a consequence of geometric and magnetic frustrations, the Gd$_{3}$Fe$_{5}$O$_{12}$ system is expected to show glassy magnetic behavior. Through a comprehensive study of DC magnetization, AC susceptibility, transverse susceptibility, and magnetocaloric effect in Gd$_{3}$Fe$_{5}$O$_{12}$ bulk and nanostructured materials, we provide physical insights into the glassy nature and magnetic relaxation mechanisms in the gadolinium iron garnet system. It is shown that bulk Gd$_{3}$Fe$_{5}$O$_{12}$ undergoes two different glassy states at temperatures below its compensation temperature with the low temperature glass properties strongly influenced by Gd ordering. However, the glassy nature is largely suppressed in Gd$_{3}$Fe$_{5}$O$_{12}$ nanoparticles in which the blocking phenomenon competes with the spin frustration effect. As particle size is decreased, the blocking effect is dominant over the spin frustration effect. As a result, the nanostructured system shows magnetic relaxation features arising mainly from superparamagnetism.