Unique Magnetic and Electric Properties

The general formula of spinel ferrite is represented by AB2O4 in which the metal cations A and B occupy tetrahedral (A) and octahedral (B) interstitial sites formed by the face centred cubic arrangement of oxygen anions. Nickel ferrite (NiFe2O4) and cobalt ferrite (CoFe2O4) are among the most studied ferrites in bulk and nano form. NiFe2O4 is a soft magnetic material utilized for applications in electronic devices, gas sensors, magnetic guided drug delivery and magnetic resonance imaging . On the other hand, cobalt ferrite (CoFe2O4) is a well-known hard magnetic material which has been explored for its high coercivity, moderate to high saturation magnetization with remarkable chemical stability and mechanical hardness . These properties make it suitable for various technological applications such as audio/video tapes, high density digital recording disks, magnetic drug delivery, radio-frequency hyperthermia, magnetic separation and magnetic resonance imaging . Both NiFe2O4 and CoFe2O4 have centrosymmetric cubic lattice of mixed spinel structure of Fd3m space group. The mixed spinel structure of CoFe2O4 and NiFe2O4 is represented as (Coδ 2+/ Niδ 2+Fe1-δ 3+)A[Co1-δ 2+/ Ni1-δ 2+/Fe1+δ 3+B where δ is the degree of inversion which depends on the synthesis conditions . There are various superexchange interactions which exist in such type of structure like Fe3+ (B)–O–Co2+ (B)/Ni2+ (B), Fe3+ (B)–O–Fe3+ (B), Fe3+ (B)–O–Fe3+ (A), Fe3+ (A)–O– Co2+ (B)/Ni2+ (B), Co2+ (A)/Ni2+ (A)–O–Fe3+ (A) and Fe3+ (B)–O–Co2+ (A)/Ni2+ (A) . These superexchange interactions are responsible for the magnetic behaviour of these ferrites . The other important parameter which determines the performance of the ferrites is its electrical conductivity.