Surface and core magnetic anisotropy in maghemite nanoparticles determined by pressure experiments

Komorida, Y.; Mito, Masaki; Deguchi, H.; Takagi, Seishi; Millán, Ángel; Silva, Nuno J. O.; Palácio, Fernando

doi:10.1063/1.3131782

Cited by 48 publications

(36 citation statements)

References 17 publications

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“…From the slope of the curve, K core = 7.7 × 10 5 erg/cm 3 . This value is between that found for the magnetocrystalline anisotropy (K 1 ) of single-domain particle of show that the changes in ΔE/k B induced by pressure are closely related to changes in V core , with the anisotropy constant associated to ΔE/k B , the magnetic anisotropy of the core K core being almost constant with P in the studied P range [27].…”

Section: Discussionsupporting

confidence: 50%

Effects of pressure on maghemite nanoparticles with a core/shell structure

Komorida

Mito

Deguchi

et al. 2010

Journal of Magnetism and Magnetic Materials

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The magnetic property and intra-particle structure of the γ phase of Fe 2 O 3 (maghemite) nanoparticles with a diameter (D) of 5.1 ± 0.5 nm were investigated through AC and DC magnetic measurements and powder X-ray diffraction (XRD) measurements at pressures (P) up to 27.7 kbar. Maghemite originally exhibits ferrimagnetic ordering at about 918 K, and has an inverse spinel structure with vacancies. Maghemite nanoparticles studied here consist of a superparamagnetic core with structural periodicity and a disordered shell without the periodicity. The DC and AC susceptibilities reveal that the anisotropy energy barrier (ΔE/k B ) decreases at the initial pressure (P ≤ 3.8 kbar), recovering at P ≥ 3.8 kbar. The physical mechanism associated to the change of ΔE/k B with P suggests that it is associated to the existence of a down-and-up fluctuation of the number of Fe 3+ ions constituting the core at the pressure threshold of about 4 kbar. This phenomenon was confirmed by the analysis of the 1 XRD measurement using Scherrer's formula. The core volume decreased down to about 45 % of the initial volume at P = 2.5 kbar. The result series obtained in this study indicates that both the core and the shell are unstable against external stress, and that, at higher pressure, the core can be restructured. ΔE/k B is approximately proportional to the volume associated to the ordered fraction of the nanoparticles as seen from XRD, V core . From this dependence it is possible to separate the core/shell contribution to ΔE/k B and estimate a core and surface anisotropy constants, with the core one being of the order of magnetocrystaline anisotropy of maghemite. As for the structural experiments, the data for D = 12.8 ± 3.2 nm at pressures of up to P = 33.6 kbar are also presented.

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Section: Discussionsupporting

confidence: 50%

Effects of pressure on maghemite nanoparticles with a core/shell structure

Komorida

Mito

Deguchi

et al. 2010

Journal of Magnetism and Magnetic Materials

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“…The effect of pressure in the NPs core and surface is distinct, allowing disentanglement of core and shell magnetic properties. This is the case of the anisotropy energy barrier in spherical maghemite NPs; while at room pressure only an effective value can be obtained, with increasing pressure core and shell size have a different response and so does the effective anisotropy energy, such that core and shell components of the anisotropy energy can be extracted [4].…”

Section: Introductionmentioning

confidence: 99%

“…In the case of nanoparticles (NPs), pressure modifies the transition temperature [1], the susceptibility and magnetization [2,3], the hysteresis cycles [2] and the effective anisotropy energy barrier [4]. The effect of pressure in the NPs core and surface is distinct, allowing disentanglement of core and shell magnetic properties.…”

Section: Introductionmentioning

confidence: 99%

Pressure effects in hollow and solid iron oxide nanoparticles

Silva

Saisho

Mito

et al. 2013

Journal of Magnetism and Magnetic Materials

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We report a study on the pressure response of the anisotropy energy of hollow and solid maghemite nanoparticles. The differences between the maghemite samples are understood in terms of size, magnetic anisotropy and shape of the particles. In particular, the differences between hollow and solid samples are due to the different shape of the nanoparticles and by comparing both pressure responses it is possible to conclude that the shell has a larger pressure response when compared to the core.

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“…Despite the widespread use of the pV function defined in Equation (3) in materials research, for instance in X-rays diffraction and Raman spectroscopy [20,21], to the best of our knowledge there is no previously reported application of this function in the investigation of the composites' mechanical properties. The performed analysis constitutes a typical optimization process in pursuit of the model parameters yielding the minimum value of the selected objective functions.…”

Section: Computational Approachmentioning

confidence: 99%

A detailed study of α-relaxation in epoxy/carbon nanoparticles composites using computational analysis

Stimoniaris¹,

Stergiou²,

Delides³

2012

Express Polym. Lett.

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Abstract. Nanocomposites were fabricated based on diglycidyl ether of bisphenol A (DGEBA), cured with triethylenetetramine (TETA) and filled with: a) high conductivity carbon black (CB) and b) amino-functionalized multiwalled carbon nanotubes (MWCNTs). The full dynamic mechanical analysis (DMA) spectra, obtained for the thermomechanical characterization of the partially cured DGEBA/TETA/CB and water saturated DGEBA/TETA/MWCNT composites, reveal a complex behaviour as the !-relaxation appears to consist of more than one individual peaks. By employing some basic calculations along with an optimization procedure, which utilizes the pseudo-Voigt profile function, the experimental data have been successfully analyzed. In fact, additional values of sub-glass transition temperature (T i ) corresponding to subrelaxation mechanisms were introduced besides the dominant process. Thus, the physical sense of multiple networks in the composites is investigated and the glass transition temperature T g is more precisely determined, as the DMA !-relaxation peaks can be reconstructed by the accumulation of individual peaks. Additionally, a novel term, the index of the network homogeneity (IH), is proposed to effectively characterize the degree of statistical perfection of the network.

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Surface and core magnetic anisotropy in maghemite nanoparticles determined by pressure experiments

Cited by 48 publications

References 17 publications

Effects of pressure on maghemite nanoparticles with a core/shell structure

Effects of pressure on maghemite nanoparticles with a core/shell structure

Pressure effects in hollow and solid iron oxide nanoparticles

A detailed study of α-relaxation in epoxy/carbon nanoparticles composites using computational analysis

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