Mossbauer studies of superparamagnetic [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] nanoparticles

Superparamagnetic [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] nanonoparticle is fabricated by a sol-gel method. The magnetic and structural properties as a function of annealing temperature were characterized by using X-ray diffactometry (XRD), Mossbauer spectroscopy, and vibrating sample magnetometry (VSM) as well as scanning electron microscope (SEM). [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] powder that was annealed at 573 K has spinel structure and behaved superparamagnetically at room temperature. The estimated size of superparammagnetic [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] nanoparticle is around 7 nm. The hyperfine fields of the A and B patterns at 4.2 K were found to be 514 and 481 kOe, respectively. The blocking temperature ([T.sub.B]) of superparammagnetic [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] nanoparticle is about 90 K. The magnetic anisotropy constant of [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4] nanoparticle were calculated to be 1.6 x [10.sup.6] erg/[cm.sup.3] Index Terms--Blocking temperature, Mossbauer spectroscopy, [Ni.sub.0.5][Zn.sub.0.5][Fe.sub.2][O.sub.4], sol-gel method, superparamagnetic.