Magnetic Behavior of ZnFe₂O₄ Nanoparticles: Effects of a Solid Matrix and the Particle Size

Abstract

ZnFe 2 O 4 nanoparticles with sizes between 3 and 20 nm have been prepared nonembedded and embedded in an amorphous SiO 2 matrix. All the samples are ferrimagnetic below the blocking temperature that presents similar values for all of them, indicated by the maxima in the ZFC/FC curves. However, the embedded nanoparticles with sizes between 3 and 7 nm present much higher values of coercive field than the nonembedded particles. The fact that particles with different sizes present similar blocking temperature values suggests that they have similar anisotropy energy, and this has been justified using experimental anisotropy constants determined for different sized nanoparticles. Although the matrix can increase the surface anisotropy of the particles, it would not greatly affect the core anisotropy. Taking this into account, it can be justified that embedded particles present a higher coercive field but similar blocking temperature than nonembedded particles. From the variation of the coercive field as a function of the particle size, the limit between the single-domain and multidomain regions seems to be in the range of 15-18 nm. The range of temperature in which the samples behave as superparamagnetic has been estimated from the plots of the inverse susceptibility versus temperature. The particle size and the inversion parameter control the magnetization value that seems to determine the transition temperature from superparamagnetic to paramagnetic behavior.

Effects of pH Value, Reaction Time, and Filling Pressure on the Hydrothermal Synthesis of ZnFe₂O₄ Nanoparticles

“…To discuss the variation of the coercivities in ZFO-50 and ZFO-70, the magnetic domain dependence on the nanoparticle size should be considered. It has been reported that ferrite nanoparticles usually transfer from multi-domains to a single domain state when the particle size was decreased below the critical diameter of 15-18 nm [22]. In the multi-domain state, the surface effects can lead to large anisotropy energy in nanoparticles due to the uncompensated surface spin [1].…”

Magnetic properties of ZnFe2O4 nanoparticles

“…This leads to the observed narrowing of the resonance line and an internal magnetic field averaging out to zero with temperature increase. The value of T B for ferrite nanoparticles depends on the particle sizes, synthesis conditions, and applied magnetic field [20,21]. For ZFO nanoparticles with a mean size of ∼11 nm, the reported values of T B were in a wide 21−150 K temperature range [21][22][23].…”

Influence of silicon dioxide medium on the structural and electrical properties of nickel zinc ferrite

“…The intensity of a diffraction pattern at a particular Bragg angle depends on the number of scattering centers in the medium. All the reported works regarding X-ray analysis of ferrite/silica composites treated the SiO 2 matrix as amorphous [9][10][11][12][13][14][15][16][17][18][19][20]. Hence, the intensity of the X-ray at any Bragg angle is contributed by both the ferrite phase and the background amorphous medium.…”

“…There are several studies on the effect of the silica matrix on the structural and magnetic properties of NZFO [10,11,[13][14][15], ZFO [16,17], and NFO [18,19] by changing the ferrite content in SiO 2 . It is found that the amorphous medium has a strong influence on the size of ferrite crystallites and their magnetic properties.…”