Spin-Canting and Magnetic Anisotropy in Ultrasmall CoFe₂O₄Nanoparticles

Abstract

The magnetic properties of cobalt ferrite nanoparticles dispersed in a silica matrix in samples with different concentrations (5 and 10 wt% CoFe2O 4) and same particle size (3 nm) were studied by magnetization, DC and AC susceptibility, and Mossbauer spectroscopy measurements. The results indicate that the particles are very weakly interacting. The magnetic properties (saturation magnetization, anisotropy constant, and spin-canting) are discussed in relation to the cation distribution.

Magnetism in Nanoparticles: Beyond the Effect of Particle Size

“…In fact, the thermal analysis of the precursors shows that the exothermic peak correspond- www.chemeurj.org ing to autocombustion reaction shifts, indicating a different speed of the particle formation and growth. [26] A systematic and accurate Mçssbauer investigation [6] was carried out in order to gain information on these aspects. Mçssbauer spectra at low temperature consist of sextets (Figures 6a-b, full symbols) due to magnetic hyperfine splitting of magnetically blocked iron ions.…”

“…Below T B , the nanoparticles display ferro-or ferrimagnetic behaviour with hysteresis loops, similarly to bulk materials. [2,5,6] An enlightening demonstration of the strong correlation between particle size and magnetic properties has been achieved by comparing the log-normal fits of particle size distributions, obtained by TEM observations in three cobalt ferrite-silica nanocomposites, with the distributions of anisotropy energy barriers, obtained by studying the thermal dependence of the magnetization measured with the Thermal Remanent Magnetization (TRM) protocol (Figure 1 a and b). The two kinds of curves follow nearly perfectly parallel paths, showing that a control of the particle size and size distribution is reflected in the control of magnetic anisotropy and then in that of magnetic behaviour.…”

“…The two kinds of curves follow nearly perfectly parallel paths, showing that a control of the particle size and size distribution is reflected in the control of magnetic anisotropy and then in that of magnetic behaviour. [6,7] However, it was soon realized that the magnetic behaviour of nanomaterials is far more complicated. A survey of the results reported so far reveals some ambiguities.…”

Enhanced magnetic behavior, exchange bias effect, and dielectric property of BiFeO3 incorporated in (BiFeO3)0.50 (Co0.4Zn0.4Cu0.2 Fe2O4)0.5 nanocomposite

“…Here the temperature T B can be regarded as the highest temperature at which the ZFC and FC magnetizations are bifurcated which corresponds to the larger particles in the system and the ZFC magnetization decreases below the temperature T P due to the smaller group of particles in the system. [49][50][51][52][53] For monodisperse particles, the maximum point in the ZFC magnetization curve defines the blocking temperature and it is very close to the temperature of bifurcation between ZFC and FC curves. In this case the ZFC magnetization curve below the blocking temperature (T < T B ) may be regarded as the magnetization of the just unblocked particles and the FC curve for T < T B represents the magnetization of both unblocked and blocked particles, and hence the difference in these two curves would represents the magnetization of the blocked particles.…”

“…49 This observation was reported by many workers. 50,51 where they have stated that the bifurcation point is the blocking temperature (T B ) and the maximum point in the ZFC curve is 2014) designated as T P . Actually, T B is defined as the temperature below which the magnetic moment of nanoparticle does not relax during the time scale of the measurement.…”