Nanoscale driven structural changes and associated superparamagnetism in magnetically diluted Ni-Zn ferrites

Abstract

The investigation under study deals with the combustion synthesis of nanocrystalline Mg substituted Nickel Zinc Ferrites i.e., MgxNi0.6-xZn0.4Fe2O4 (x = 0.0 to 0.6) using malic acid dihydrazide as novel fuel and the effect of Magnesium substitution on structural and magnetic properties. The nanocrystalline monophasic nature of “as prepared” MgxNi0.6-xZn0.4Fe2O4 (x = 0.0 to 0.6) has been confirmed from XRD and Raman spectroscopic studies and crystallite sizes were found to be in the range of 19-25 nm which nearly matches with TEM. The RT and low temperature magnetization studies indicate continuous decrease in magnetization with increase in Mg substitution. Whereas, the hysteretic behavior diminished with the emergence of superparamagnetism is observed in all the samples as the Mg content increases. The decrease in MS with increase in Mg concentration is attributed to the replacement of magnetic Ni+2 ions with non-magnetic Mg+2 ions and also to the enhancement of Y-K angle by cation redistribution. The variation of AC susceptibility with temperature exhibits broad maxima, indicating distribution of particle sizes in sample with the existence of single domain and superparamagnetic type of domain structure. The susceptibility decreases continuously beyond x = 0.4 till 0.6, and samples exhibits only superparamagnetism. The AC susceptibility studies also shows decrease in Curie temperature (TC) with increase in x for MgxNi0.6-xZn0.4Fe2O4 (x = 0.0 to 0.6) resulting from weakening of A-B interaction. The ZFC-FC studies along with Mӧssbauer studies were also corroborated the proposed existence of dominant superparamagnetism with increase in Mg concentration.