Analysis of Magnetic After-Effect Spectra in Titanium-Doped Magnetite

Walz, F.; Torres, L.; Bendimya, K.; Francisco, C. de; Kronmüller, H.

doi:10.1002/1521-396x(199712)164:2<805::aid-pssa805>3.0.co;2-n

Cited by 24 publications

(55 citation statements)

References 32 publications

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“…Second, there is also considerable variation in the disaccommodation spectra peak temperatures for magnetites from different origins [11,30].…”

Section: Discussionmentioning

confidence: 79%

“…First, the different timescales of the measurements are likely to be important as the positions of the peaks in the disaccommodation spectra are known to be time dependent; the peaks shift to lower temperatures as the measurement time increases due to the thermally activated nature of the processes contributing to disaccommodation. For example, for a polycrystalline magnetite sample a disaccommodation peak located at 320 K measured at 2 s, shifted to 290 K on measuring after 180 s [30]. As the viscosity measurements were made over longer timescales, i.e., > 2000 s, it would be expected that the positions of the viscosity peaks would be shifted to even lower temperatures.…”

Section: Discussionmentioning

confidence: 81%

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Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

Muxworthy

Williams

2006

Journal of Magnetism and Magnetic Materials

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Low-temperature viscous acquisition and decay measurements above and below the Verwey transition have been measured for a selection of natural and synthetic multidomain magnetite samples. A strong correlation between the viscosity spectra and published disaccommodation spectra was found, where disaccommodation reflects electron mobility. Assuming the viscosity is controlled by identical mechanisms as disaccommodation, the reduction in electron mobility below the Verwey transition is found to significantly increase viscous acquisition and decay rates over the time scales measured (1-3000 seconds). Although strongly affecting the viscosity, disaccommodation processes do not appear to control the rate of change of viscosity with time, i.e., the viscosity curvature. It is suggested that the curvature is controlled by the shape of relaxation-time distributions, which is approximately the same for all the magnetite samples studied. In addition, the acquisition and decay curvature parameters mirror each other when plotted as a function of temperature, inferring that at any given temperature the acquisition and decay processes are identical.PAC numbers: 75.60.Lr, 75.60.Ch, 9.60.Pn.

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“…Second, there is also considerable variation in the disaccommodation spectra peak temperatures for magnetites from different origins [11,30].…”

Section: Discussionmentioning

confidence: 79%

Section: Discussionmentioning

confidence: 81%

Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

Muxworthy

Williams

2006

Journal of Magnetism and Magnetic Materials

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“…At room temperature, electron hopping between Fe 2+ and Fe 3+ ions in the B sites (and possibly also in the A sites) occurs on timescales shorter than the Mössbauer measurement time, and consequently the Fe 2+ and Fe 3+ are blurred together in the Mössbauer spectra, yielding a broadened composite sextet with an average oxidation state of Fe 2.5+ . Measurements at 4.2 K, where electron hopping is suppressed (e.g., Walz et al, ), allow sharper distinction of iron valence states, and the application of a strong field allows clearer resolution of sites by shifting the A‐site and B‐site subspectra in opposite directions. Because of the dominance of the B sublattice moment and negative A‐B exchange interactions, the moments of the B‐site cations align with the applied field and those of the A site in the antiparallel direction, effectively decreasing and increasing the B‐ and A‐site hyperfine fields, respectively (e.g., Daniels & Rosencwaig, ; Hamdeh et al, ; Murad & Cashion, ).…”

Section: Methodsmentioning

confidence: 99%

Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

Bowles

Lappe

Jackson

et al. 2019

Geochem Geophys Geosyst

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Previous work has documented time‐ and temperature‐dependent variations in the Curie temperature (Tc) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic‐scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X‐ray magnetic circular dichroism (XMCD) and Mössbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in Tc, but Mössbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe2+/Fe3+ does not play a role in the observed Tc changes. Rather, the data are consistent with vacancy‐enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.

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“…1, 2) from lowest temperatures (T < 4 K), down to a plateau of minute strength, extending between 55 and 75 K, thereby surpassing a Debye-type maximum near 50 K of annealing-depending strength. This behaviour is at variance to that of e À -irradiated stoichiometric magnetite where, immediately after irradiation, the corresponding tunneling zone is found to be strongly suppressed [15]; it ressembles, however, that of magnetite compounds submitted to charge-order perturbations by quenching-in of octahedral vacancies [29 to 31] or doping with ionic impurities like Ti 4 [32,33], Ga 3 [34], Mn 2 [35,36], etc.…”

Section: The Mae Spectrum Of Electron-irradiated Yigmentioning

confidence: 99%

Charge Transport Mechanisms in Single Crystalline Yttrium Iron Garnet as Resolved by Magnetic Relaxations

Walz¹,

Torres

Íñiguez

et al. 2000

phys. stat. sol. (a)

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Single crystalline Yttrium Iron Garnet (YIG) has been irradiated at T % 80 K with 3 MeV electrons to a dose of ! 10 19 e À cm À2 and the recovery of the induced lattice damages, after systematic annealing over the temperature range 80 K < T a < 1400 K, is carefully investigated by means of magnetic after-effect (MAE) spectroscopy, covering the range 4 K < T < 500 K. The wide extension of recovery is attributed, besides to Fe 3 and Fe 2 interstitials and their associated d-and a-site vacancies, especially to the larger, and hence less mobile, Y 3 interstitialcies and their c-type vacant sites. The obtained data allow to resolve various charge transport mechanisms: (i) tunneling of electrons in combination with intra-atomic excitations in the low-temperature zone (4 K < T < 55 K); (ii) small-polaron hopping, extended over the range 80 K < T < 350 K; (iii) primarily radiation-induced, Debye-type ionic reorientation processes with peak temperatures near to 250, 325 and 400 K.Einkristalliner Yttrium-Eisen-Granat wurde bei T % 80 K mit 3 MeV-Elektronen auf eine Dosis von ! 10 19 e À cm À2 bestrahlt und die anschlieûende Erholung der Gitterfehler, nach systematischem Anlassen u È ber einen Temperaturbereich von 80 K < T a < 1400 K, mit Hilfe magnetischer Nachwirkungsspektroskopie im Gebiet 4 K < T < 500 K sorgfa È ltig untersucht. Der weit ausgedehnte Erholungsbereich wird, neben Fe 3 und Fe 2 Zwischengitter-Ionen und deren zugeho È riger d-und a-Platz Leerstellen, hauptsa È chlich den gro È ûeren, und damit unbeweglicheren, Y 3 ZwischengitterIonen und ihren c-Platz Leerstellen zugeordnet. Die gewonnenen Daten erlauben eine deutliche Unterscheidung folgender Ladungstransport-Vorga È nge: (i) Tunneln von Elektronen in Verbindung mit intra-atomarer Anregung (4 K < T < 55 K); (ii) Klein-Polaron-Hu È pfen im Bereich 80 K < T < 350 K; (iii) bestrahlungsinduzierte, durch Ionenspru È nge verursachte Debye-Prozesse mit Maximumtemperaturen von 250, 325 und 400 K.

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Analysis of Magnetic After-Effect Spectra in Titanium-Doped Magnetite

Cited by 24 publications

References 32 publications

Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

Charge Transport Mechanisms in Single Crystalline Yttrium Iron Garnet as Resolved by Magnetic Relaxations

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