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Ka̧kol, Z.; Honig, J. M.

doi:10.1103/physrevb.40.9090

Cited by 141 publications

(65 citation statements)

References 21 publications

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“…At a critical value of the ratio R c = U / W Ϸ 2.2 ͑where U is interionic Coulomb potential and W is bandwidth͒, the Verwey transition will disappear. This model has been proved and fully in agreement with various experimental situations such as impurity substitution, 27 pressure effect 28 on Verwey transition, the deviation from the ideal stochiometery 29 and Verwey transition in lowdimensional systems. 5 All these experiments proposed the variation of bandwidth and interionic Coulomb interaction and its effect on Verwey transition temperature.…”

Section: Resultssupporting

confidence: 54%

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Kumar

Khan

Srivastava

et al. 2006

Journal of Applied Physics

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The effect of swift heavy ion ͑SHI͒ irradiation ͑190 MeV Ag͒ on structural, electrical transport and magnetic properties of epitaxial magnetite ͑Fe 3 O 4 ͒ thin films ͑thickness ϳ70 nm͒ grown on MgO͗100͘ oriented substrate have been investigated. The x-ray diffraction shows that at low fluence values up to 5 ϫ 10 11 ions/ cm 2 , the strain in the films is relaxed, whereas, at higher fluence range 1 ϫ 10 12 -1 ϫ 10 13 ions/ cm 2 , the epitaxial relationship with the substrate is lost along with a phase transformation from magnetite to more oxidized magnetite phase ͑i.e., maghemite͒. The Verwey transition temperature measured by electrical transport is found to increase from 109 to 117 K with the low fluence SHI irradiation, which is related to the irradiation induced strain relaxation and structural modifications. At higher fluences the system did not show Verwey transition and the resistance is also increased. The similar results were obtained by magnetization studies. The observed magnetization at 1 T field is increased at low fluence suggesting the reduction of areas with frustrated exchange interactions associated with the cationic arrangement at the anti phase boundaries. At higher fluences it decreases monotonically, indicating the emergence of other phases. The observed modifications are explained on the basis of structural strain and disorder induced by swift heavy ions, which lead to modification of the interionic Coulomb potential at octahedral sublattices and bandwidth in this system.

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Section: Resultssupporting

confidence: 54%

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Kumar

Khan

Srivastava

et al. 2006

Journal of Applied Physics

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“…It is known that a significant change in X in Fe 3ϪX O 4 from 0.015 to 0 leads to a change in M s of only 1%. 9 As established from HRXRD, RS, and resistivity measurements, the change in the film's stoichiometry caused by annealing in air was marginal. Such a small change cannot explain a massive 14% increase observed in the value of M 1T .…”

Section: Resultsmentioning

confidence: 99%

Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

Yinqing¹,

Jin²,

Shvets³

2004

Journal of Applied Physics

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The effect of thermo-chemical treatment on the ease of saturation in a magnetic field of epitaxial magnetite ͑100͒ thin films grown on MgO ͑100͒ substrates was investigated. It was found that the films maintained a fully strained state with the MgO substrate during the treatment in air. No other iron oxide phase apart from the magnetite was observed in the treated film. Yet, remarkably the treated films showed a higher magnetization compared to that of original ones. A model involving a change in antiferromagnetic coupling at the antiphase boundaries during the treatment is proposed.

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“…In this paper, we discuss the magnetic signature of this transition that appears as a very sharp feature ͑in good single crystals 8,9 ͒ at the Verwey temperature T V . Similar to the Verwey transition itself, the physics of this magnetic anomaly is still debatable.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, magnetite, especially in the form of nanoparticles, is very sensitive to oxidation by oxygen, which might result in stoichiometric changes in the crystals and disturbance of the transition. 15 In this paper, we compare biologically produced magnetite nanocrystals, which have an almost perfect crystal structure and a well-defined shape and size, to large high-quality crystals 8,9 as well as to conventional, synthetic magnetite nanoparticles. The goal was to study the Verwey transition in a superparamagnetic system ͑without magnetic domains͒ and identify possible influences of particle size, shape, and crystalline magnetic anisotropies as well as interparticle interactions on the magnetic signature of the Verwey transition.…”

Section: Introductionmentioning

confidence: 99%

Magnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite

Prozorov

Mallapragada

et al. 2007

Phys. Rev. B

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The magnetic properties of biologically produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high-quality single crystals. The magnetic feature at the Verwey temperature TV was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which TB < TV, where TB is the superparamagnetic blocking temperature. For nanocrystals organized in chains, the effective blocking temperature TB > TV and the Verwey transition is sharply defined. No correlation between particle size and TV was found. Furthermore, measurements of M (H,T,time) suggest that magnetosome chains behave as long magnetic dipoles where the local magnetic field is directed along the chain. This result confirms that time-logarithmic magnetic relaxation is due to the collective (dipolar) nature of the barrier for magnetic moment reorientation. The magnetic properties of biologically produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high-quality single crystals. The magnetic feature at the Verwey temperature T V was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which T B Ͻ T V , where T B is the superparamagnetic blocking temperature. For nanocrystals organized in chains, the effective blocking temperature T B Ͼ T V and the Verwey transition is sharply defined. No correlation between particle size and T V was found. Furthermore, measurements of M͑H , T , time͒ suggest that magnetosome chains behave as long magnetic dipoles where the local magnetic field is directed along the chain. This result confirms that time-logarithmic magnetic relaxation is due to the collective ͑dipolar͒ nature of the barrier for magnetic moment reorientation.

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Influence of deviations from ideal stoichiometry on the anisotropy parameters of magnetiteFe3(1−δ)

Cited by 141 publications

References 21 publications

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Swift heavy ion irradiation-induced modifications in structural, magnetic and electrical transport properties of epitaxial magnetite thin films

Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

Magnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite

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