Tuning the surface anisotropy in Fe-doped NiO nanoparticles

Abstract

Ni(1-x)FexO nanoparticles have been obtained by the co-precipitation chemical route. X-ray diffraction analyses using Rietveld refinement have shown a slight decrease in the microstrain and mean particle size as a function of the Fe content. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves show superparamagnetic behavior at high temperatures and a low temperature peak (at T = 11 K), which is enhanced with increasing Fe concentration. Unusual behavior of the coercive field in the low temperature region and an exchange bias behavior were also observed. A decrease in the Fe concentration induces an increase in the exchange bias field. We argue that these behaviors can be linked with the strengthening of surface anisotropy caused by the incorporation of Fe ions.

Magnetic properties of NiO (nickel oxide) nanoparticles: Blocking temperature and Neel temperature

“…3(c)). Similar magnetic behavior of NiO nanoparticles has been reported in the literature, where the two ZFC peaks were interpreted as the spin-glass freezing temperature and the particle blocking temperature [4,7,22,25,27,29,32,42]. These NiO systems have generally been described in the literature in terms of an exchange-coupled spherical bilayer composed of an inner antiferromagnetic core and an outer shell of uncompensated spins.…”

“…Moreover, incomplete compensation of spins in the antiferromagnetic core (due to structural defects and nonstoichiometry) is also expected to contribute to µ p . Special attention has been paid to the impact of interparticle interactions in previous studies [22,23,25,27] [27]. Magnetization and AC magnetic susceptibility measurements indicated that interparticle interactions shift the distribution of the core moment blocking temperature towards higher temperature (64 K→85 K) and lead to a reduction of the magnetization dynamics [27].…”

Nickel/Iron Oxide Nanocrystals with a Nonequilibrium Phase: Controlling Size, Shape, and Composition

“…While a similar double peak complex was seen in Fe x O nanoparticles, 79 it was absent in 10 at% Fe-doped NiO nanoparticles, 47 suggesting that the low transition peak is dependent on the increasing presence of Fe 2+ . Given the existence of Fe 3 O 4 surface states in the Fe x O nanoparticles, 79 we propose that the low temperature peak arises from the presence and subsequent oxidation of Fe 2+ at the surface of the nanoparticles, resulting in the formation of a surface region with unique magnetic properties.…”

“…47 Here, we present mixed metal nickel−iron oxide nanoparticles possessing a rocksalt crystal structure, synthesized via solution-phase decomposition of metal oleate precursors. The nanoparticle products maintain a single-crystal rocksalt structure over almost the entire range of nickel:iron ratios.…”

Doping Effect on the Magnetic and Structural Properties in Co and Co95TM5 (TM = Fe, Cr and Mn) Nanoparticles

“…Other behavior observed in these same samples is appearing of a peak in the ZFC curve at about 7 K. In general this peak can be explained by two points of view: i) the blocking temperature of smallest particles, probably, the hexagonal Co nanoparticles which increase with its concentration [15] and/or ii) the large surface effect originate by the disordered spins on the surface of the smallest particles [15,16]. In order to reinforece our assumption, we present in Figure 4 the magnetization as a function of applied magnetic field curves (MvsH) performed at a T = 2 K for all samples.…”