Synthesis, characterization and FC–ZFC magnetization studies of cobalt substituted lithium nano ferrites

• Crystallite size of [Li0.5Fe0.5]1−xCoxFe2O4, 0≤x≤1.0 ranges from 37 nm to 42 nm.
• Blocking temperature (Tb) of Li0.1Co0.8 Fe2.1O4 and CoFe2O4 is at around 350 K.
• These two ferrites show superparamagnetic behavior above 350 K.
• These ferrites are desirable for bio-medical applications.

Cobalt substituted Lithium Nano ferrites with the chemical composition [Li0.5Fe0.5]1−xCoxFe2O4 (where x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized through Citrate-Gel auto combustion technique. Structural characterization of the prepared ferrites was carried by X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). XRD analysis has confirmed the formation cubic spinel structure of the ferrite compositions with a particle size ranging from 37 nm to 42 nm. The SEM images represent large agglomeration of the nano particles of the ferrite samples with broader grain size distribution. Temperature dependent magnetic properties of [Li0.5Fe0.5]1−xCoxFe2O4 for two compositions with cobalt content x=0.8 and x=1.0 were carried out using Vibrating sample magnetometer (VSM). The magnetization as a function of an applied field ±10 T was carried out at temperatures 5 K and 310 K. Field cooled (FC) and Zero field cooled (ZFC) magnetization measurements under an applied field of 100 Oe and 1 KOe in the temperature range of 5–375 K were performed. These measurements have resulted the blocking temperature (Tb) at around 350 K i.e. above room temperature for both the ferrites. Below this temperature the ferrites show ferromagnetic behavior and above which superparamagnetic behavior where the coercivity and remanence magnetization are almost zero. Such behavior makes the ferrites to be desirable for biomedical applications.