Thermally activated Bloch wall motion

Siemers, D.; Nembach, E.

doi:10.1016/0375-9601(78)90725-9

Cited by 6 publications

(9 citation statements)

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“…This does not mean that these obstacles are the same as the most coercive obstacles carrying the low field 1,. As far as the wall's area interacting with an obstacle is somewhat constant when h varies, it is expected that the activation volume of this obstacle decreases when h increases (Siemers & Nembach 1978). Thus, the obstacles responsible for the sharp increase in magnetic viscosity near h = 40 Oe could correspond as well to those carrying the softest component of J,.…”

Section: A C T I V a T I O N V O L U M E A N D Viscosity Fieldmentioning

confidence: 99%

Thermally Activated Magnetic Viscosity In Natural Multidomain Titanomagnetite

Bina¹,

Prévot²

1994

Geophysical Journal International

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S U M M A R Y Magnetic viscosity and hysteresis versus temperature and field have been studied between room and Curie temperatures on two selected coarse-grained submarine basalts carrying multidomain (MD) low Curie temperature titanomagnetite. These samples exhibit typical characteristics of magnetic viscosity in rocks, including imperfect linearity of the magnetization change with logarithm of time and a large increase in viscosity with temperature, followed by a decrease occurring some 30°-400 below the average Curie point of the rock sample. The field dependence of magnetic viscosity exhibits a maximum located slightly above the sample coercive force. Other experiments, reported elsewherd, show that diffusion plays a negligible role in these rocks. Thus, magnetic viscosity is probably entirely of thermal origin. In spite of the MD characteristics of our samples at room temperature, alternating field (AF) demagnetization of remanence shows, in one of them, the presence of a large component of high coercivity of PSD or SD origin. The remanence of the other sample seems to be wholly of MD origin. The thermal dependences of magnetic viscosity and irreversible susceptibility are only approximately similar, and the field dependences are quite different. This indicates that the proportionality of irreversible susceptibility with magnetic viscosity predicted by the NCel and the Street and Wooley theories of thermal fluctuations in MD grains does not hold for natural titanomagnetite like ours, even though it is verified for synthetic ferromagnetic substances. However, our experimental data are compatible with the fundamentals of the theory of thermal fluctuations if we assume that the pinning of Bloch walls in natural titanomagnetite is due to several kinds of energy barriers with a broad distribution of both activation volumes v;, and critical fields h,. Thus, the remanent magnetization acquired in a low field (1 Oe) applied for 1 d at room temperature is found to be pinned by two categories of defects with (1) v d = 7 x 10-15cm3 and h , = 3 Oe and (2) v , = 1 X 10-'5cm3 and h , = 15 Oe. Using a (va, h,) diagram to represent each barrier, we show that the 'blocking' (or 'unblocking') curves are quite dissimilar for field and time effects, just as for SD particles. This indicates that the proportionality between magnetic viscosity and irreversible susceptibility requires particular distributions of energy barriers in the ( v a , h c ) plane and cannot be considered as a general characteristic of thermally activated magnetic viscosity.Key words: magnetic viscosity, multidomain particles, submarine basalt, thermal fluctuations, titanomagnetite. commonly observed in rocks. It is not exceptional that the remanent magnetization acquired in nature by this process I N T R O D U C T I O NA time-dependence of magnetization in a constant applied (viscous remanent magnetization or VRM) is larger in field (magnetic after-effect or magnetic viscosity) is magnitude than the primary remanence which preserves the 495

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Section: A C T I V a T I O N V O L U M E A N D Viscosity Fieldmentioning

confidence: 99%

Thermally Activated Magnetic Viscosity In Natural Multidomain Titanomagnetite

Bina¹,

Prévot²

1994

Geophysical Journal International

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“…Pour tourner cette difficulté, [Two examples of the virgin curve (H -Hé).] (4) Remarque : De nombreuses figures : 9,13,14,16,20,21,22,24,26,28,36, correspondent à des enregistrements obtenus sur une table traçante x, y ou y(t). Nous connaissons les échelles sur les axes, mais nous ignorons en général l'origine.…”

Section: (( Sauts De Barkhausen » ; (( Bruit De Bark-unclassified

“…En particulier, la fréquence pour laquelle la puissance de bruit est maximale est très voisine de llàt. De 24 représente l'évolution, en fonction de la vitesse moyenne x de la paroi, d'un cycle d'hystérésis de très faible amplitude. L'excursion de champ et la température ( ~ 300 K) restent constantes pour les cinq enregistrements reproduits.…”

Section: Les Résultats Expérimentaux -321unclassified

“…On peut également analyser la disparition des grands sauts au voisinage de la vitesse critique x2. La figure 28 reproduit trois enregistrements du bruit Barkhausen correspondant aux cycles c, d, e de la figure 24. Dans l'enregistrement 28c, on observe une succession d'impulsions bien distinctes et reproductibles lorsque la paroi balaie plusieurs fois la même région du cristal.…”

Section: Les Résultats Expérimentaux -321unclassified

“…Les fluctuations thermiques n'ont pas à fournir toute l'énergie nécessaire pour franchir les obstacles, comme ce serait le cas en champ nul, mais seulement une petite partie de celle-ci (cf. référence [24]).…”

Section: Une Statistique Gaussienne Des Pentes D'inflexionunclassified

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Quelques aspects statistiques des processus d'aimantation dans les corps ferromagnétiques. Cas du déplacement d'une seule paroi de Bloch à 180° dans un milieu monocristallin aléatoirement perturbé

Vergne

Cotillard

Porteseil

1981

Rev. Phys. Appl. (Paris)

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Analysis of the Extraordinary Viscous Magnetic Domain Wall Motion in NiFe Films

Nembach

1979

Phys. Stat. Sol. (a)

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Experimental data, published by Bostanjoglo and Gemünd, on the extraordinary viscous domain wall motion in thin oxidized films of 83 at % NiFe are analyzed. It is assumed that the velocity v of the wall is governed by the interaction of the wall with defects present in the film and that this interaction can be overcome by thermal activation. The activation energy E is calculated from the experimental data v(H, T) (H applied magnetic field, T temperature). E is a unique smooth function of H. From the obtained relation E(H), information on the force‐distance profile of the interaction between defect and wall is derived.

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Thermally activated Bloch wall motion

Cited by 6 publications

References 4 publications

Thermally Activated Magnetic Viscosity In Natural Multidomain Titanomagnetite

Thermally Activated Magnetic Viscosity In Natural Multidomain Titanomagnetite

Quelques aspects statistiques des processus d'aimantation dans les corps ferromagnétiques. Cas du déplacement d'une seule paroi de Bloch à 180° dans un milieu monocristallin aléatoirement perturbé

Analysis of the Extraordinary Viscous Magnetic Domain Wall Motion in NiFe Films

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