Investigation of superparamagnetism in MgCr0.9Fe1.1O4 nano-ferrites synthesized by the Citrate-gel method

• MgFe2O4 and MgCr0.9Fe1.1O4 nano-ferrites with a particle size of 23 nm and 7.6 nm were synthesized by the Citrate-gel auto-combustion method.
• MgFe2O4 nano-ferrites showed super-paramagnetic behavior above room temperature.
• MgCr0.9Fe1.1O4 showed super-paramagnetic behavior due to its low particle size 7.6 nm with the blocking temperature 94.5 K.
• Above this blocking temperature MgCr0.9Fe1.1O4 showed no hysteresis and below this they showed hysteresis which indicates the super-paramagnetic behavior.
• MgCr0.9Fe1.1O4 finds applications in targeted drug delivery and in Magnetic Resonance imaging due to its super-paramagnetic behavior.

MgFe2O4 and MgCr0.9Fe1.1O4 nano-ferrites were synthesized using Citrate-gel technique and the magnetic properties were studied. The crystallite sizes of the prepared MgFe2O4 and MgCr0.9Fe1.1O4 nano-particles were estimated from X-ray diffraction patterns as 23 nm and 7.6 nm respectively. Magnetization as a function of field (±10 T) and temperature was measured using a vibrating sample magnetometer for temperature ranging from 5 K to 300 K. From the temperature dependence of both the field cooled (FC) and the zero-field cooled (ZFC) magnetization measurements under a field of 100 Oe, blocking temperature (Tb) for MgFe2O4 was obtained at above room temperature whereas for MgCr0.9Fe1.1O4 it was obtained at 94 K. The M–H curves for MgCr0.9Fe1.1O4 nanoferrites indicated the presence of ferromagnetic behavior with hysteresis below the blocking temperature (Tb). A large coercive force of about 1100 Oe was found at 5 K. The phenomenon suggests that the synthesized Cr substituted Mg nano-ferrite with chemical composition MgCr0.9Fe1.1O4 shows superparamagnetic behavior above the blocking temperature 94 K. This nature makes these materials to be used in biomedical applications like magnetically guided drug delivery and Magnetic Resonance Imaging (MRI).