Magnetic Aftereffects in Titanium Ferrites

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

doi:10.1002/1521-396x(199705)161:1<289::aid-pssa289>3.0.co;2-3

Cited by 16 publications

(36 citation statements)

References 27 publications

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“…Meantimes we have investigated a series of related spinel-type ferrites over the full temperature range 4 K`T`500 K, under various experimental conditions such as, i.e., vacancy-doping [2 to 6], presence of internal stresses ( [7], cf. [3 to 6]), induction of intrinsic point defects by electron-irradiation [8], doping with impurity ions like Ba 2 [9], Ni 2 [10], Zn 2 [11,12], Ti 4 [13,14], Ga 2 [15]. Against this background of experience [16] we found it interesting and necessary to provide the present results concerning the low-temperature behaviour of Mn-ferrites.…”

Section: Introductionmentioning

confidence: 89%

Analysis of Magnetic After-Effects in Manganese Ferrites

Walz¹,

Rivas

Brabers³

et al. 1999

phys. stat. sol. (a)

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The low‐temperature (4 > T > 125), electron‐induced magnetic after‐effect (MAE) spectra of vacancy‐doped manganese ferrites, Fe3—x—ΔMnxO4 (0.002 ≤ x ≤ 0.8 and δ ≈︂ × 10—3, are investigated in detail. The tunnelling‐induced MAEs (4 K > T > 35 K are severely affected in the presence of even smallest Mn contents (x ≤ 0.002). The hopping regime, though strongly modified upon continued doping — i.e. by narrowing and low‐temperature shifting (≤50 K) — persists over the whole concentration range. Its high‐temperature collapse remains accompanied by a pronounced susceptibility jump, thus indicating preservation of a residual, second‐order Verwey‐like crystallographic phase transition. The vacancy‐mediated process III (300 K) and its Mn‐dependent satellite II (≈︂380 K) are quantitatively analyzed and the, also Mn‐induced, process IV (200 K) interpreted in a novel way in terms of intrinsic interstitials.

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Section: Introductionmentioning

confidence: 89%

Analysis of Magnetic After-Effects in Manganese Ferrites

Walz¹,

Rivas

Brabers³

et al. 1999

phys. stat. sol. (a)

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“…Regarding magnetite, and according with the notation of [4][5][6], we distinguish two very different features: for Ti and Sn substitution it is observed the splitting of the III peak into three relaxation processes, called III, IV (275 K) and IV' (250 K), together with the presence of two additional processes, called I (420-440 K) and II (385-400 K), at higher temperatures. On the other hand, for Si doping the III peak only splits into III and IV processes, and no disaccommodation peaks are observed at temperatures around 400 K. This different behaviour is also observed in the evolution of Verwey transition with increasing substitution rate: whereas Ti-and Sn-doped magnetite behave in a similar manner, with diminution of Verwey transition temperature and strong modification of electronic hopping at temperatures up to 120 K [5], Si substitution only alters the amplitude of the above-mentioned electronic process. The splitting of III peak into III, IV and IV' processes, despite it is only disclosed in the titanium doped isochronal spectra, becomes also evident in tin substituted samples after the fitting procedure with superposition of thermally activated exponential contributions to magnetic permeability [6], from which the activation energies calculated are about 0.80 eV for III peak, 0.67 eV for IV peak and 0.58 eV for IV' peak.…”

Section: Resultsmentioning

confidence: 95%

“…In Fig. 3 it is also added the well-known isochronal spectrum of undoped, polycrystalline magnetite, characterized by the so-called III peak centred at about 300 K. In all the cases, the logarithmic relaxation process due to electronic transfer between Fe 2+ and Fe 3+ up to Verwey temperature (120 K) [2,5] is observed with low tetravalent doping amount.…”

Section: Resultsmentioning

confidence: 99%

“…It consists on the time variation of the mobility of domain walls after a magnetic shock, due to the rearrangement or diffussion of anisotropic point defects within the Bloch walls. In previous works we have analyzed the effect of the introduction of Ti 4+ cations in both the hexagonal [3] and the cubic lattice [4,5], as well as the Sn 4+ doping in magnetite [6]. In this paper we summarize the effect that the most common substitutions of tetravalent cations (Ti, Sn, Si) have on the magnetic disaccommodation regarding undoped magnetite.…”

Section: Introductionmentioning

confidence: 99%

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Effect of tetravalent substitutions on the magnetic disaccommodation in magnetite

Hernández-Gómez

Bendimya

Francisco

et al. 2006

Phys. Status Solidi (c)

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PACS 75.50. Gg, 75.60.Lr The relaxation of the initial magnetic permeability has been measured in polycrystalline tetravalent-doped magnetite with nominal composition Me x Fe 3-x O 4 (Me: Ti, Sn, Si) with 0 < x < 0.4. The samples have been sintered at 1400 ºC in a reducing CO 2 atmosphere. The time decay of the initial permeability after sample demagnetization has been represented by means of isochronal curves in the temperature range between 80 K and 500 K.The isochronal disaccommodation spectra for Ti and Sn-doped magnetite show the splitting of the well known process III of vacancy-doped magnetite (at 300 K) into three peaks at 240 K (IV peak), 270 K (IV') and 300 K (III). This behaviour is ascribed to the presence of tetravalent cations in octahedral sites within the spinel lattice. Two peaks at 400 K (II) and 440 K (I) also emerge, owing to the existence of pairs Me 4+ -Fe 2+ cations as well as long range diffusion of ferrous cations. The differences found among these substitutions are explained in terms of the different cationic radii of tin and titanium. On the other hand only the III and IV processes are detected in Si-doped magnetite samples, due to the preferential occupation by Si cations of tetrahedral sites according to their smaller size.

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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: 93%

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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Magnetic Aftereffects in Titanium Ferrites

Cited by 16 publications

References 27 publications

Analysis of Magnetic After-Effects in Manganese Ferrites

Analysis of Magnetic After-Effects in Manganese Ferrites

Effect of tetravalent substitutions on the magnetic disaccommodation in magnetite

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

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