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C. Kittel

Bio: C. Kittel is an academic researcher from Bell Labs. The author has contributed to research in topics: Absorption (electromagnetic radiation) & Domain (software engineering). The author has an hindex of 15, co-authored 19 publications receiving 5888 citations.

Papers
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Journal Article
TL;DR: The theory of ferromagnetic resonance absorption was extended in this paper to include the effect of the shape of the specimen and, in the case of a single crystal, of crystal orientation.
Abstract: The theory of ferromagnetic resonance absorption previously developed is extended to include the effect of the shape of the specimen and, in the case of a single crystal, the effect of crystal orientation. The resonance condition may be written ${\ensuremath{\omega}}_{0}=\ensuremath{\gamma}{H}_{\mathrm{eff}}$, where ${H}_{\mathrm{eff}}$ is equal to ${(\mathrm{BH})}^{\frac{1}{2}}$ for a plane surface, $H+2\ensuremath{\pi}M$ for a long circular cylinder, and $H$ for a sphere; the latter two values apply only to the situation in which the eddy current skin depth is large in comparison with the radius of the specimen. In the case of an uniaxial crystal with the axis parallel to the static magnetic field, the value of $H$ to be used in the resonance conditions is increased by $\frac{2K}{M}$, where $K$ is the anisotropy constant. The case of a cubic crystal is also considered. A detailed discussion of macroscopic eddy current effects is given, and it is shown that the usual eddy current losses do not introduce damping terms into the expression for the permeability, when properly interpreted.

1,816 citations

Journal ArticleDOI
C. Kittel1

1,571 citations

Journal ArticleDOI
C. Kittel1
TL;DR: The theory of ferromagnetic resonance absorption was extended in this paper to include the effect of the shape of the specimen and, in the case of a single crystal, of crystal orientation.
Abstract: The theory of ferromagnetic resonance absorption previously developed is extended to include the effect of the shape of the specimen and, in the case of a single crystal, the effect of crystal orientation. The resonance condition may be written ${\ensuremath{\omega}}_{0}=\ensuremath{\gamma}{H}_{\mathrm{eff}}$, where ${H}_{\mathrm{eff}}$ is equal to ${(\mathrm{BH})}^{\frac{1}{2}}$ for a plane surface, $H+2\ensuremath{\pi}M$ for a long circular cylinder, and $H$ for a sphere; the latter two values apply only to the situation in which the eddy current skin depth is large in comparison with the radius of the specimen. In the case of an uniaxial crystal with the axis parallel to the static magnetic field, the value of $H$ to be used in the resonance conditions is increased by $\frac{2K}{M}$, where $K$ is the anisotropy constant. The case of a cubic crystal is also considered. A detailed discussion of macroscopic eddy current effects is given, and it is shown that the usual eddy current losses do not introduce damping terms into the expression for the permeability, when properly interpreted.

1,281 citations

Journal ArticleDOI
TL;DR: In this paper, the velocity of propagation of a single domain boundary in a crystal of silicon iron with a simple domain structure is given by a relation of the form $v=G(H\ensuremath{-}{H}_{0})$, where $G$ is a constant and H is the starting field.
Abstract: Experimental results are given on the velocity of propagation of a single domain boundary in a crystal of silicon iron with a simple domain structure. In weak applied magnetic fields (\ensuremath{\sim}0.003 oersted) the velocity is given by a relation of the form $v=G(H\ensuremath{-}{H}_{0})$, where $G$ is a constant \ensuremath{\sim}4 cm/sec./oersted in this crystal, and ${H}_{0}\ensuremath{\cong}0.003$ oersted is the starting field. Calculation of the eddy current losses accompanying the motion of a plane boundary gives a theoretical expression for $G$ in good agreement with experimental values; the predicted linear dependence on the resistivity was approximately verified by measurements at 78\ifmmode^\circ\else\textdegree\fi{}, 194\ifmmode^\circ\else\textdegree\fi{}, and 293\ifmmode^\circ\else\textdegree\fi{}K. In stronger fields (g5 oersteds) there is evidence that the wall closes on itself, and the experimental velocity of collapse of the wall as deduced from flux changes agrees with the theoretical result based on a model of eddy current losses accompanying a collapsing cylindrical boundary. The results have a bearing on the well-known eddy current anomaly, namely, the fact that the total loss in a ferromagnetic material undergoing a.c. magnetization is often two or three times larger than the eddy-current and hysteresis losses calculated in the usual way assuming a spatially uniform and isotropic classical permeability.

388 citations

Journal ArticleDOI
C. Kittel1
TL;DR: In this article, the behavior of glasses is interpreted in terms of an approximately constant free path for the lattice phonons, so that the conductivity decreases roughly with the specific heat.
Abstract: The thermal conductivity of glasses decreases with decreasing temperature, while the conductivity of crystalline substances increases with decreasing temperature. The behavior of glasses is interpreted in terms of an approximately constant free path for the lattice phonons, so that the conductivity decreases roughly with the specific heat. The value of the phonon mean free path at room temperature is of the order of magnitude of the scale of the disorder in the structure of glasses as determined from x-ray evidence---that is, of the order of 7A. This is about the size of the unit cell of the crystalline forms of silica.

369 citations


Cited by
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01 Sep 1955
TL;DR: In this paper, the authors restrict their attention to the ferrites and a few other closely related materials, which are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present.
Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

2,659 citations

Journal ArticleDOI
TL;DR: In this paper, a reformulation of the phenomenological theory of the magnetization field was proposed to take large non-eddy-current damping into account in thin Permalloy sheets.
Abstract: In 1955, a phenomenological theory of ferromagnetism was well established and had been corroborated by a considerable amount of experimental data. However, there were problems in the phenomenological theory of the dynamics of the magnetization field. The Landau-Lifshitz equation for damping of the motion of the magnetization field could not account for the large noneddy-current damping in thin Permalloy sheets. The problem undertaken herein is a reformulation of the theory in a way that is more consistent with the theory of damping in other physical systems in order to be able to take large damping into account.

2,181 citations

Journal ArticleDOI
TL;DR: The phenomenology of exchange bias and related effects in nanostructures is reviewed in this paper, where the main applications of exchange biased nanostructure are summarized and the implications of the nanometer dimensions on some of the existing exchange bias theories are briefly discussed.

1,721 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured the loss per cycle (sinusoidal flux waveform) versus magnetizing frequency f/sub m/(0 > 0) for a single cycle.
Abstract: Measurements are reported of the loss per cycle (sinusoidal flux waveform) versus magnetizing frequency f/sub m/(0 >

1,587 citations

Journal ArticleDOI
TL;DR: In this article, the authors review the progress in this field of laser manipulation of magnetic order in a systematic way and show that the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale.
Abstract: The interaction of subpicosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of subpicosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, the manipulation of magnetic order by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. Understanding the underlying mechanisms implies understanding the interaction of photons with charges, spins, and lattice, and the angular momentum transfer between them. This paper will review the progress in this field of laser manipulation of magnetic order in a systematic way. Starting with a historical introduction, the interaction of light with magnetically ordered matter is discussed. By investigating metals, semiconductors, and dielectrics, the roles of nearly free electrons, charge redistributions, and spin-orbit and spin-lattice interactions can partly be separated, and effects due to heating can be distinguished from those that are not. It will be shown that there is a fundamental distinction between processes that involve the actual absorption of photons and those that do not. It turns out that for the latter, the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale. Thus, circularly and linearly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday and inverse Cotton-Mouton effects, respectively. The recent progress in the understanding of magneto-optical effects on the femtosecond time scale together with the mentioned inverse, optomagnetic effects promises a bright future for this field of ultrafast optical manipulation of magnetic order or femtomagnetism.

1,449 citations