Determination of magnetic anisotropy distribution and anisotropy constant of manganese spinel ferrite nanoparticles

SQUID magnetometry and Mossbauer spectroscopy has been combined to quantita tively characterize the superparamagnetic relaxation of MnFe2O4 nanoparticl es with a mean size of 7.4 nm. The key parameter for understanding and cont rolling the superparamagnetic properties of nanoparticles, the anisotropy c onstant K has been determined as 0.056 J/cm(3) for this nanoparticulate sam ple, which is more than 20 times higher than bulk MnFe2O4 materials. The la rge enhancement of magnetic anisotropy in these nanoparticles suggests the possibility of strong interactions between the magnetic core and shell of t he nanoparticles. The quantitative characterization of the 7.4 mn MnFe2O4 n anoparticles also shows the preexponential factor ro as 0.95 x 10(-10) s. T his ro value is in a good agreement with the theoretical value. Such an agr eement is possibly as the result of minimal interparticle interaction in Mn Fe2O4 nanoparticulate sample.