Unusually high coercivity and critical single-domain size of nearly monodispersed CoFe2O4 nanoparticles

Abstract

Nearly monodispersed CoFe2O4 nanoparticles with average sizes between 8 and 100 nm were synthesized by using seed-mediated growth dominant coprecipitation and modified oxidation methods. X-ray diffraction and Mössbauer spectroscopy analyses confirmed the spinel phase and a stoichiometric composition of (Co0.25Fe0.75)[Co0.75Fe1.25]O4 for powders with different particle diameters. Rotational hysteresis loss (Wr) analysis showed an average switching field (Hp) of 17 kOe and a magnetic anisotropy field (Hk) of 38 kOe for the 40 nm CoFe2O4 particles. The corresponding magnetocrystalline anisotropy energy constant (K) was about 5.1×106 erg/cc. The Hc and Hp results suggest that the critical single-domain size of CoFe2O4 is about 40 nm. The room temperature coercivity (Hc) of the 40 nm CoFe2O4 particles is found to be as high as 4.65 kOe.

Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres

“…The shape of the magnetization loops is determined by the mixture of single-domain and multidomain nanoparticles [14], and the magnetization does not saturate at the maximum applied magnetic field of 10 kOe, due to the strong magnetic anisotropy (> 30 kOe) of the CFO nanoparticles [15].…”

Inverse magnetocaloric effect in sol–gel derived nanosized cobalt ferrite

“…The ratio M r /M s (magnetic remanence/saturation magnetization) throws light on the exchange interactions and magnetocrystalline anisotropy associated with the ferrite nanoparticles [26]. According to the Stoner-Wohlfarth model [27], theoretical value of M r /M s is 0.5 for noninteracting uniaxial single domain particles with the easy axis being randomly oriented.…”

Mössbauer and magnetic study of Co x Fe3--x O4 nanoparticles

“…Cobalt ferrite bulk material (CoFe2O4) is known to be a ferrimagnetic material with very high cubic magnetocrystalline anisotropy leading to high theoretical coercivity: 25.2 kOe at 5 K (maximum observed at 2 K is 22 kOe) and 5.4 kOe at 300 K, and a saturation magnetization of 93.9 emu/g at 5 K and 80.8 emu/g at 300 K [2][3][4]. Concerning our samples, the absence of coercivity, remanence and saturation at 295 K for the sample milled during 5 h suggests that this material behaves as a superparamagnet at room temperature.…”