Interparticle and collective states of interactions in mechanically milled Fe/CoO nanocomposites

The effect of high-energy milling on magnetic properties of Fe/CoO nanocomposites has been studied. Formation of pure phase polycrystalline sample having size in the range 15-20 nm is confirmed from micro-structural analysis. Mössbauer spectroscopy indicates the formation of a broad distribution of particle sizes in the samples milled for higher duration. Enhancement in coercivity as well as exchange field is confirmed from magnetic hysteresis measurements. High-field bifurcation in temperature dependent magnetization measurement points toward the formation of spin-glass like state. Wait time dependent magnetization relaxation confirmed this possibility and is supported by the field cooled memory effect. Complexity arises when the absence of memory effect is observed in time dependent magnetic relaxation measurement. Polydispersity and defects are argued to be possible causes for observed spin-glass behavior.