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Introduction to Magnetic Materials

TL;DR: In this paper, the authors present materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.
Abstract: Introduction to Magnetic Materials, 2nd Edition covers the basics of magnetic quantities, magnetic devices, and materials used in practice. While retaining much of the original, this revision now covers SQUID and alternating gradient magnetometers, magnetic force microscope, Kerr effect, amorphous alloys, rare-earth magnets, SI Units alongside cgs units, and other up-to-date topics. In addition, the authors have added an entirely new chapter on information materials. The text presents materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.
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2,428 citations

Journal ArticleDOI
TL;DR: In this paper, a mathematical model of the hysteresis mechanisms in ferromagnets is presented based on existing ideas of domain wall motion including both bending and translation, which gives rise to a frictional force opposing the movement of domain walls.

1,989 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarize the recent developments in the synthesis, structural characterization, properties, and applications of amorphous and nanocrystalline soft magnetic materials, including: kinetics and thermodynamics, structure, microstructure, and intrinsic and extrinsic magnetic properties.

1,453 citations


Additional excerpts

  • ...[28,32,35,43] and review articles as in Ref....

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Journal ArticleDOI
TL;DR: In this paper, a detailed study of static and dynamic magnetic behavior of Fe3O4 nanoparticles with average particle sizes ranging from 5 to 150 nm is presented, and the existence of surface spin disorder can be inferred from the decrease of saturation magnetization MS at low temperatures, as the average particle size is reduced.
Abstract: We present a detailed study of static and dynamic magnetic behavior of Fe3O4 nanoparticles with average particle sizes 〈d〉 ranging from 5 to 150 nm. Bulk-like properties such as saturation magnetization, hyperfine parameters, coercive field, and Verwey transition are observed in 150 nm particles. For decreasing particle size, the Verwey temperature, TV, shifts down to ∼20 K for 〈d〉=50 nm and is no longer observable for smaller particles. The smallest particles (〈d〉=5 nm) display superparamagnetic behavior at room temperature, with transition to a blocked state at TB∼45 K, which depends on the applied field. The existence of surface spin disorder can be inferred from the decrease of saturation magnetization MS at low temperatures, as the average particle size is reduced. This disordered surface did not show effects of exchange coupling to the particle core, as observed from hysteresis loops after field cooling in a 7 T magnetic field. For particles with 〈d〉=5 nm, dynamic ac susceptibility measurements show...

1,265 citations

Journal ArticleDOI
Dieter Weller1, Andreas Moser
TL;DR: In this article, the authors discuss thermal effects in the framework of basic Arrhenius-Neel statistical switching models and reveal the onset of thermal decay at "stability ratios" (k/sub u/V/K/sub B/T)/sub 0//spl sime/35 /spl plusmn/ 2.
Abstract: In current longitudinal magnetic recording media, high areal density and low noise are achieved by statistical averaging over several hundred weakly coupled ferromagnetic grains per bit cell. Continued scaling to smaller bit and grain sizes, however, may prompt spontaneous magnetization reversal processes when the stored energy per particle starts competing with thermal energy, thereby limiting the achievable areal density. Charap et al. have predicted this to occur at about 40 Gbits/in/sup 2/. This paper discusses thermal effects in the framework of basic Arrhenius-Neel statistical switching models. It is emphasized that magnetization decay is intimately related to high-speed-switching phenomena. Thickness-, temperature- and bit-density dependent recording experiments reveal the onset of thermal decay at "stability ratios" (K/sub u/V/K/sub B/T)/sub 0//spl sime/35 /spl plusmn/ 2. The stability requirement is grain size dispersion dependent and shifts to about 60 for projected 40 Gbits/in/sup 2/ conditions and ten-year storage times. Higher anisotropy and coercivity media with reduced grain sizes are logical extensions of the current technology until write field limitations are reached. Future advancements will rely on deviations from traditional scaling. Squarer bits may reduce destabilizing stray fields inside the bit transitions. Perpendicular recording may shift the onset of thermal effects to higher bit densities. Enhanced signal processing may allow signal retrieval with fewer grains per bit. Finally, single grain per bit recording may be envisioned in patterned media, with lithographically defined bits.

1,223 citations