Effects of disordered surface structure on the magnetic properties of nanocrystalline MnFe₂O₄

In this study, a detailed investigation of the magnetic properties of nanocrystalline manganese ferrite (MnFe₂O₄) (average crystallite size is 8.4 nm) synthesized by ball milling technique is presented. DC and AC magnetization measurements reveal that disordered surface spin structure plays an important role on the magnetic behavior of nanocrystalline MnFe₂O₄. Temperature dependent DC field biased susceptibility measurements, performed by field cooled and zero field-cooled procedures, have shown a clear field and temperature dependent irreversibility. Although, the real part of the ZFC susceptibility possesses a reduction up to 25 K, FC susceptibility exhibits the conventional increasing trend. The temperature at which the difference between the FC and ZFC lines becomes zero is inversely proportional to the DC bias field. While the difference between the two lines reduces by the increase of the field, the temperature where ZFC curves make a dip is determined to be independent of the DC bias field.