On the phase transition(s) of magnetite at low temperatures

Rigo, M. O.; Marêché, J.F.; Brabers, V.A.M.

doi:10.1080/13642818308228568

Cited by 18 publications

(5 citation statements)

References 26 publications

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“…It is important to note that the 13 nm magnetite sample used in these studies was extensively characterized and found to be chemically pure (except for adsorbed water impurity), phase pure, and highly crystalline. While it is not certain that this anomalous behavior is related to the Verwey transition, it is observed that the heat capacity of 13 nm magnetite does not have the anomaly at T v seen in the heat capacity of bulk magnetite. ,, In spite of this uncertainty, it can be concluded that crystal size is an important factor as it is the only variable that has significantly changed between this study and other studies of pure magnetite.…”

Section: Discussioncontrasting

confidence: 62%

“…While it is not certain that this anomalous behavior is related to the Verwey transition, it is observed that the heat capacity of 13 nm magnetite does not have the anomaly at T v seen in the heat capacity of bulk magnetite. 16,17,25 In spite of this uncertainty, it can be concluded that crystal size is an important factor as it is the only variable that has significantly changed between this study and other studies of pure magnetite.…”

Section: Discussionmentioning

confidence: 61%

“…The Verwey transition typically appears as an anomaly appears in the heat capacity around T = 120 K ( T v ). Some controversy surrounds the exact shape of the heat capacity peak; some authors report a single peak − in this region, while others have observed two or more. ,− In those papers that report multiple peaks, there is no consistency in the peak separation or peak shape. Some report peaks separated by several degrees with others having incompletely resolved peaks.…”

Section: Introductionmentioning

confidence: 99%

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Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)

et al. 2010

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The Verwey transition in magnetite (Fe 3 O 4 ) has been studied extensively with a wide assortment of experimental techniques to investigate the effects of impurities, oxygen stoichiometry, and crystal quality; however, no studies have tested the effects of crystal size on the Verwey transition. In this study, the heat capacity of a magnetite powder with an average crystallite size of 13 nm was measured in the temperature range of 0.5-350 K. No obvious anomaly was observed in the heat capacity in the vicinity of 120 K, yet the measurements exhibited unusual thermal behaviors between 50 and 90 K with relaxation times increasing from an average of 25 min to as much as 5 h in this temperature interval. The behavior is typical of a phase transition, so the lack of a distinct anomaly suggests either the phenomenon is spread out over a large temperature interval with little enthalpy or an insulating phase with different thermal conductivities appears. The heat capacity below 90 K was dependent on cooling rate with an inconsistent anomaly found below 4 K. The results suggest that the Verwey transition has a particle-size dependence. Additionally, theoretical fits below 15 K suggest that magnetite nanoparticles display anisotropic ferrimagnetic behavior and a superparamagnetic contribution to the heat capacity which are properties not observed in bulk magnetite.

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Section: Discussioncontrasting

confidence: 62%

Section: Discussionmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

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Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)

et al. 2010

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“…Our MAE analysis revealed significant deviations between the spectra of the powdered and perfect crystals which could be unambiguously associated with the presence of internal stresses and B-type vacancies which had been introduced during the powdering process [184]. On the occasion of this test we were also able to finally exclude, as had already been done previously [185], the occurrence of a further, long-debated anomaly at 10 K [172,[179][180][181][182][183], which initially had been reported by Todo et al [186]. These final MAE results have been confirmed by further specific heat investigations performed since then [187,188].…”

Section: Elimination Of Multi-stage (N >supporting

confidence: 54%

“…[82] clear results concerning this problem, cf section 3.2.2, the relevance of a second peak near 110 K, besides the major one at T v , remained under discussion for many further years. Whereas Rigo et al [84,179,180] regarded this second peak-obtained on powdered material-as purely intrinsic, Gmelin et al [181,182] and Shepherd et al [183], on well prepared single crystals, could not detect any trace of this 110 K anomaly. The final 'knockout' for the thermal bifurcation, as an intrisic process of perfect magnetite, was accomplished by means of the MAE [184].…”

Section: Elimination Of Multi-stage (N >mentioning

confidence: 96%

The Verwey transition - a topical review

Walz¹

2002

J. Phys.: Condens. Matter

698

651

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This review encompasses the story of the Verwey transition in magnetite over a period of about 90 years, from its discovery up to the present. Despite this long period of thorough investigation, the intricate multi-particle system Fe3O4 with its various magneto-electronic interactions is not completely understood, as yet - although considerable progress has been achieved, especially during the last two decades. It therefore appeared appropriate to subdivide this retrospect into three eras: (I) from the detection of the effect to the Verwey model (1913-1947), being followed by a period of: (II) checking, questioning and modification of Verwey's original concepts (1947-1979). Owing to prevailing under-estimation of the role of crystal preparation and qualitiy control, this period is also characterized by a series of uncertainties and erroneous statements concerning the reaction order (one or two) and type of the transition (multi-stage or single stage). These latter problems, beyond others, could definitely be solved within era (III) (1979 to the present) - in favour of a first-order, single-stage transition near 125 K - on the basis of experimental and theoretical standards established in the course of a most inspiring conference organized in 1979 by Sir Nevill Mott in Cambridge and solely devoted to the present topic. Regarding the experimental field of further research, the remarkable efficiency of magnetic after-effect (MAE) spectroscopy as a sensitive probe for quality control and investigation of low-temperature (4 KTv) into a Wigner crystal (T

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Point Defects in Electron‐Irradiated Stoichiometric Magnetite

Walz

Kronmüller

1990

Physica Status Solidi (b)

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High‐purity, stoichiometric, single crystalline magnetite (Fe3O4) has been electron (e−)‐irradiated below 45 K to a dose of 1023 electrons/m2. Radiation‐induced point defects give rise to both drastic modifications of intrinsic electronic processes and the occurrence of reorientation‐type magnetic relaxations. Both phenomena offer deeper insights into the mechanisms of (i) electronic charge transport and (ii) thermally activated reactions of interstitials and vacancies. Coordination between migration of elementary defects and corresponding anncaling stages can be established in Fe3O4 with higher precision than in any other magnetic system investigated so far.

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On the phase transition(s) of magnetite at low temperatures

Cited by 18 publications

References 26 publications

Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)

Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)

The Verwey transition - a topical review

Point Defects in Electron‐Irradiated Stoichiometric Magnetite

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On the phase transition(s) of magnetite at low temperatures

Cited by 18 publications

References 26 publications

Heat Capacity Studies of Nanocrystalline Magnetite (Fe3O4)

Heat Capacity Studies of Nanocrystalline Magnetite (Fe3O4)

The Verwey transition - a topical review

Point Defects in Electron‐Irradiated Stoichiometric Magnetite

Contact Info

Product

Resources

About

Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)

Heat Capacity Studies of Nanocrystalline Magnetite (Fe₃O₄)