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Magnetic properties and magnetic relaxation in a suspension of CoFe2O4 nanoparticles
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View: Figures


Image of FIG. 1.
FIG. 1.

(a). XRD pattern of the powder sample indexed with the (hkl) reflections of the cubic spinel; (b) TEM and (c) HRTEM images of the CoFeO nanoparticles. Electron diffraction pattern in the inset of Fig. 1(b) was indexed according to the spinel structure; (d) DSC curve for the liquid sample in the temperature range 150–240 K.

Image of FIG. 2.
FIG. 2.

Magnetic field dependence of magnetization for the liquid sample at  = 5 and 300 K. The dashed curve drawn through the  = 5 K hysteresis loop is a guide to the eye. The solid curve is the fit of the sum of Langevin functions weighted by log-normal distribution of particle sizes to the experimental data at 300 K. The inset represents resulting distribution function with σ = 0.27 and  = 6.0 nm.

Image of FIG. 3.
FIG. 3.

Temperature dependence of (a) the real part χ′ and (b) the imaginary part χ″ of the magnetic susceptibility for the liquid sample at frequencies in the range  = 1–1500 Hz. The inset in Fig. 3(a) shows the best fit of the VF law to the experimental () and () data.

Image of FIG. 4.
FIG. 4.

Frequency dependence of the imaginary part of the susceptibility at  = 148 K. The solid curve is the fit of imaginary part of the susceptibility, Eq. (1) , to the experimental data in the frequency range  = 1–500 Hz (1.84 ≤ ln ω ≤ 8.05). Inset: Fit of the real part of Eq. (1) to the experimental χ′(ln ω) data at  = 148 K.

Image of FIG. 5.
FIG. 5.

Calculated ln(1/τ) vs dependencies for selected pairs of values (, ), where particle diameter and interaction parameter are shown in the range (a)  = 6.3–5.3 nm,  = 25–73 K, (b)  = 5.8–5.2 nm,  = 1–40 K. Full symbols with error bars represent the experimental values: (a) ln(1/τ ) obtained as fitting parameters from the lower frequency peak and (b) ln(1/τ ) estimated from the measured susceptibilities at   ≥ 1000 Hz.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Magnetic properties and magnetic relaxation in a suspension of CoFe2O4 nanoparticles