A Study of Magnetic Viscosity

Street, R. A.; Woolley, J. C.

doi:10.1088/0370-1298/62/9/303

Cited by 661 publications

(262 citation statements)

References 9 publications

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“…We have determined V* exploiting sweep-rate dependence of coercivity 10 and magnetic viscosity measurements. 11 In many cases where the results have been compared, these two methods agree with each other well, so that we will restrict ourselves to the former method.…”

Section: Resultsmentioning

confidence: 90%

Magnetic properties of self-assembled Co nanowires of varying length and diameter

Zeng

Zheng

Skomski

et al. 2000

Journal of Applied Physics

272

188

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Ferromagnetic Co nanowires have been electrodeposited into self-assembled porous anodic alumina arrays. Due to their cylindrical shape, the nanowires exhibit perpendicular anisotropy. The coercivity, remanence ratio, and activation volumes of Co nanowires depend strongly on the length, diameter, and spacing of the nanowires. Both coercivity and thermal activation volume increase with increasing wire length, while for constant center-to-center spacing, coercivity decreases and thermal activation volume increases with increasing wire diameter. The behavior of the nanowires is explained qualitatively in terms of localized magnetization reversal.

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Section: Resultsmentioning

confidence: 90%

Magnetic properties of self-assembled Co nanowires of varying length and diameter

Zeng

Zheng

Skomski

et al. 2000

Journal of Applied Physics

272

188

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“…6 In this letter, V* was derived from its relationship with magnetic viscosity and irreversible susceptibility. 14,17 CoPt:C films were cosputtered onto water-cooled Si͑100͒ substrates from pure Co, Pt, and C targets. better than 3ϫ10 Ϫ7 Torr and the Ar pressure is 10 mTorr.…”

mentioning

confidence: 99%

Nanocomposite CoPt:C films for extremely high-density recording

Liu

Möser

et al. 1999

Applied Physics Letters

162

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Nanocomposite CoPt:C films were investigated as potential media for extremely high-density recording. An annealing temperature of over 600 °C is necessary to form nanocomposite CoPt:C films consisting of C matrix and fct CoPt nanocrystallites with grain sizes of 8–20 nm and coercivities of 3–12 kOe. Coercivity and grain size increase with increasing annealing temperature and decreasing C concentration and they are insensitive to film thickness. The average activation volumes are about 0.9×10−18 cm3. The properties of these nanocomposite CoPt:C films can be tailored to satisfy the thermal stability, coercivity, and media noise requirements for extremely high-density recording.

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“…If the system is composed of particles all of the same size and whose magnetizations can only relax by one process which has a characteristic time r, then the time-dependence of the magnetization, M{t), behaves as (Street and Woolley (1949)…”

Section: Magnetic Viscosity In Fine Magnetic Particlesmentioning

confidence: 99%

The physical properties of magnetic inks

1993

NDT & E International

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source• a link is made to the metadata record in Durham E-Theses• the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. {Philip Larkin, Nursery Tale) IV AbstractThe magnetic particle inspection (MPI) method is a widely used non destructive testing (NDT) technique for ferrous structures. Magnetic inks used in MPI are suspensions of fine ferro/ferrimagnetic particles which, when applied to a magnetized test specimen, deUneate surface flaws. This work is an investigation of some of the properties of magnetic ink systems and some aspects of their interaction with defect leakage flux. Reviews of magnetism, the MPI method and leakage flux at defects are given. The construction, characterization and automation of a 1.2 T electromagnet vibrating sample magnetometer, used for magnetic measurements on the inks, is described. The instrument has a resolution of better than 10"'^ JT~^ A 20 model of indication formation in MPI, based upon the simulation of many particles in the neighbourhood of a defect, is presented. Results of the role of several of the model parameters are given. Results indicate that carrier coefficients of viscosity at the lower end of the range investigated (r/ = 0.3 mPas) are optimum. The size and contrast of an indication increases with defect size. The contrast and rate of formation of contrast increase with defect aspect ratio. The effect of the contrast paint layer thickness indicates that the recommendation of the British Standard, BS 5044 (1973), is qualitatively correct. Experimental observations of particles in field gradients reveals a discrepancy between theoretical and observed behaviour which is attributed, in particular, to unobservable voids in the particles. Detailed characterization of the particles shows them to be aggregates of 20 -200 nm crystallites which are probably single domain particles. The morphology of larger aggregates is related to measurements of the low field susceptibility Evidence from intensive magnetic measurements supports the relationship between magnetic properties and aggregate characteristics. A 'Int' magnetic viscosity effect is reported. At 77 K, the coeflScient of magnetic viscosity has a maximum near the coercivity field. A cknowledgementsIt is my privilege to acknowledge the assistance and support given to me by many people during the course of this work.

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A Study of Magnetic Viscosity

Cited by 661 publications

References 9 publications

Magnetic properties of self-assembled Co nanowires of varying length and diameter

Magnetic properties of self-assembled Co nanowires of varying length and diameter

Nanocomposite CoPt:C films for extremely high-density recording

The physical properties of magnetic inks

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