Magnetic structure of small NiFe2O4 particles

Morr, A. H.; Haneda, K.

doi:10.1063/1.328979

Cited by 248 publications

(93 citation statements)

References 14 publications

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“…[15][16][17] We propose here to follow, by Mossbauer spectroscopy under applied fields of up to 12 T, the evolution of the disordered surface spins of nickel ferrite nanoparticles. Such nanoparticles are indeed well known for presenting large surface effects and lacks of reversibility under cyclic remagnetizing.…”

Section: Introductionmentioning

confidence: 99%

In-field Mossbauer study of disordered surface spins in core/shell ferrite nanoparticles

Sousa

Rechenberg

Depeyrot

et al. 2009

Journal of Applied Physics

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Structural evolution and the kinetics of Cu clustering in the amorphous phase of Fe-Cu-Nb-Si-B alloy J. Appl. Phys. 110, 033537 (2011) Room temperature long range ferromagnetic ordering in (BiFeO3)1x (PbTiO3)x nanocrystallites J. Appl. Phys. 109, 123911 (2011) Hafnium oxide thin films studied by time differential perturbed angular correlations J. Appl. Phys. 109, 113918 (2011) Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites J. Chem. Phys. 134, 174507 (2011) Additional information on J. Appl. Phys. Magnetization and Mossbauer spectroscopy measurements are performed at low temperature under high field, on nanoparticles with a nickel ferrite core and a maghemite shell. These nanoparticles present finite size and surface effects, together with exchange anisotropy. High field magnetization brings the evidences of a monodomain ordered core and surface spins freezing in disorder at low temperature. Mossbauer spectra at 4.2 K present an extra contribution from the disordered surface which is field dependent. Field and size dependences of this latter show a progressive spin alignment along the ferrite core which is size dependent. The weak surface pinning condition of the nanoparticles confirms that the spin disorder is localized in the external shell. The underfield decrease in the mean canting angle in the superficial shell is then directly related to the unidirectional exchange anisotropy through the interface between the ordered core and the disordered shell. The obtained anisotropy field H Ea scales as the inverse of the nanoparticle diameter, validating its interfacial origin. The associated anisotropy constant K Ea equals 2.5ϫ 10 −4 J / m 2 .

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Section: Introductionmentioning

confidence: 99%

In-field Mossbauer study of disordered surface spins in core/shell ferrite nanoparticles

Sousa

Rechenberg

Depeyrot

et al. 2009

Journal of Applied Physics

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“…5,[16][17][18] Evidence for the surface origin includes the linear decreasing of the saturation magnetization with temperature. 16,[19][20][21] The uncompensated moments include those arising from an odd number of AF planes, generation of vacancies and oxidation of surface atoms. 5 In studies where surface effects are highlighted, the nanoparticles are modeled as having a magnetic ordered core surrounded by a magnetically disordered shell whose thickness is estimated as about 1 nm.…”

Section: Introductionmentioning

confidence: 99%

Remanent magnetization in CoO antiferromagnetic nanoparticles

et al. 2010

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We report a study on the remanent magnetization M r induced by field cooling across the ordering temperature T N in antiferromagnetic CoO nanoparticles with different sizes. The nanoparticles are composed by a structurally and magnetically ordered core and a structurally ordered and magnetically disordered shell with a thickness of about 2 nm. The ordered core has cell parameters, moments direction, and modulus similar to those of bulk CoO. M r is shown to be proportional to the cooling field H cool . The low-temperature saturation values of M r ͓M r ͑0͔͒ in the CoO nanoparticles are about two orders of magnitude higher than those found for bulk CoO. M r / M r ͑0͒ of CoO nanoparticles scales with temperature in a single curve, independently on the magnitude of H cool and on nanoparticles size, except for temperatures near to T N since T N is size dependent.

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“…4 It exhibits noncollinear spin structure and the magnetic moment is appreciably lower than the value for the bulk material. 13 A model wherein the particle consists of a core with the collinear spin arrangement and a surface layer with the magnetic moment inclined to the direction of magnetization has been proposed. 13 Ferrite films are usually prepared by sputtering, 14 pulsed laser deposition, 15 and spray coating 16 processes.…”

Section: A Concept Of Microwave Heating With Ferrite Thin Filmsmentioning

confidence: 99%

“…13 A model wherein the particle consists of a core with the collinear spin arrangement and a surface layer with the magnetic moment inclined to the direction of magnetization has been proposed. 13 Ferrite films are usually prepared by sputtering, 14 pulsed laser deposition, 15 and spray coating 16 processes. On the other hand, sol-gel [17][18][19] and hydrothermal 20 routes of ferrite synthesis have shown increasing importance.…”

Section: A Concept Of Microwave Heating With Ferrite Thin Filmsmentioning

confidence: 99%

Structural investigations and magnetic properties of sol-gel Ni0.5Zn0.5Fe2O4 thin films for microwave heating

Gao

Rebrov

Verhoeven

et al. 2010

Journal of Applied Physics

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Nanocrystalline Ni 0.5 Zn 0.5 Fe 2 O 4 thin films have been synthesized with various grain sizes by a sol-gel method on polycrystalline silicon substrates. The morphology, magnetic, and microwave absorption properties of the films calcined in the 673-1073 K range were studied with x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, vibrating sample magnetometry, and evanescent microwave microscopy. All films were uniform without microcracks. Increasing the calcination temperature from 873 to 1073 K and time from 1 to 3 h resulted in an increase of the grain size from 12 to 27 nm. The saturation and remnant magnetization increased with increasing the grain size, while the coercivity demonstrated a maximum near a critical grain size of 21 nm due to the transition from monodomain to multidomain behavior. The complex permittivity of the Ni-Zn ferrite films was measured in the frequency range of 2-15 GHz. The heating behavior was studied in a multimode microwave cavity at 2.4 GHz. The highest microwave heating rate in the temperature range of 315-355 K was observed in the film close to the critical grain size.

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Magnetic structure of small NiFe2O4 particles

Cited by 248 publications

References 14 publications

In-field Mossbauer study of disordered surface spins in core/shell ferrite nanoparticles

In-field Mossbauer study of disordered surface spins in core/shell ferrite nanoparticles

Remanent magnetization in CoO antiferromagnetic nanoparticles

Structural investigations and magnetic properties of sol-gel Ni0.5Zn0.5Fe2O4 thin films for microwave heating

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