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Showing papers on "Magnetization published in 1980"


Journal ArticleDOI
TL;DR: In this article, a new method was developed to measure the saturation magnetostriction of a thin amorphous ribbon based on the use of small-angle magnetization rotation, which measured the change in anisotropy field caused by the tensile stress.
Abstract: A new method was developed to measure the saturation magnetostriction of a thin amorphous ribbon. It is based on the use of small-angle magnetization rotation to measure the change in anisotropy field caused by the tensile stress. Measurements have been performed on Metglas 2826, 2605, and Co-Si-B amorphous ribbons. The maximum experimental error of the measurement was estimated to be about ±5 percent. It is shown that the sensitivity of the method depends on the shape anisotropy field. The estimated sensitivity was about 2 × 10-7for Metglas 2826 ribbon with 1.8 mm × 40 μm × 12 cm in dimensions.

235 citations


Journal ArticleDOI
TL;DR: In this article, an approximate analytic solution of the differential equation for magnetization in a cooling system gives for TB:e (TB)/kT = 1n(1.78Cθ) where e is the activation energy for rotation of magnetic moments, k is Boltzmann's constant, and C is the frequency factor (∼1010 Hz).
Abstract: Acquisition of TRM by a cooling assemblage of identical monodomain grains involves a transition from superparamagnetic to blocked behavior over a narrow but indefinite range of temperature. Blocking temperature may, nevertheless, be precisely defined by comparing the blocked magnetization, after cooling, with the curve of equilibrium magnetization against temperature. At the blocking temperature TB the relaxation time τ of the magnetization is of the same order as the cooling time constant θ, which is the time required for τ to increase by a factor e. An approximate analytic solution of the differential equation for magnetization in a cooling system gives for TB:e (TB)/kT = 1n(1.78Cθ) where e is the activation energy for rotation of magnetic moments, k is Boltzmann's constant, and C is the frequency factor (∼1010 Hz). Because e varies with temperature, the cooling time constant θ is given by 1/θ = (1/kTB)(de/dT - e/TB)dT/dt. The 95% blocking interval is about 7.2θ. For steady cooling it is reasonable to assume θ to be constant through this interval; small deviations from constancy have a negligible effect upon TB. In small external fields the variable grain geometry to be found within a real assemblage can be incorporated in a parameter e0, which is the activation energy at O°C. Curves of e0 against TB for magnetite and haematite, at cooling rates from 6°C per minute to 3°C per million years, show that (1) a change in e0 by a factor of 2 corresponds to 12 orders of magnitude change in cooling rate and (2) for a broad distribution of grain sizes a large proportion of the size range will acquire their magnetization within 100°C–200°C of the Curie point. Using these curves, blocking temperature in cooling assemblages can be related to laboratory demagnetization temperatures; the differences are greater at slower cooling rates and lower temperatures and tend to zero as the Curie temperature is approached. Intensity of magnetization should increase by a few percent for each order of magnitude decrease in cooling rate. Magnetization acquired at temperatures near the Curie point should dominate in a chemically homogenous monodomain assemblage with a broad spread of grain sizes. Possible tests of the theory and its application to the determination of cooling history are discussed.

219 citations


Journal ArticleDOI
TL;DR: In this paper, a complete phenomenological analysis is given for the case of uniaxial anisotropy in terms of K1, K2, K3, K4, K5, K6, K7, K8, K9, K10, K11, K12, K13, K14, K15, K16, K17, K18, K19, K20, K21, K22, K23, K24, K25, K26, K27, K28, K29, K30,

182 citations


Journal ArticleDOI
Ammon Aharony1, E. Pytte1
TL;DR: In this article, the leading terms in the magnetic equation of state are calculated for models with random fields and random uniaxial anisotropies for dimensionalities $dl4$.
Abstract: The leading terms in the magnetic equation of state are calculated for models with random fields and random uniaxial anisotropies for dimensionalities $dl4$. In the random anisotropy case we find a new low-temperature phase, in which the magnetization vanishes but the zero-field susceptibility is infinite, because of algebraically decaying correlations. No phase transition is found for the random field case.

141 citations


Journal ArticleDOI
01 Jul 1980-Nature
TL;DR: In this paper, a theory for important magnetization processes such as magnetic viscosity and the production of a moment on cooling in a magnetic field is presented, where the results for viscous phenomena differ from those obtained by others in that the time dependence of the viscosities depends on the size distribution of the magnetic grains.
Abstract: A theory for important magnetization processes such as magnetic viscosity and the production of a moment on cooling in a magnetic field is presented here. The results for viscous phenomena differ from those obtained by others in that the time dependence of the viscosity depends on the size distribution of the magnetic grains. The moment produced on cooling in a magnetic field is calculated for an arbitrary distribution of grains for the first time. The effect of the cooling rate on the moment produced is found not only to be independent of that distribution but also of the temperature dependence of the saturation magnetization.

141 citations


Journal ArticleDOI
TL;DR: Polarized and unpolarized neutron measurements have been carried out on a YCo5 single crystal. as discussed by the authors showed that the moment of one of the two cobalt sites (Co1) has a very large orbital contribution as well as an important asphericity.
Abstract: Polarised and unpolarised neutron measurements have been carried out on a YCo5 single crystal. These have allowed the crystal structure to be refined and the magnetisation density distribution of this compound to be determined. The analysis of these results indicates that the moment of one of the two cobalt sites (Co1) has a very large orbital contribution as well as an important asphericity. These features are discussed in terms of the well known and unusually large magneto-crystalline anisotropy of Co in YCo5.

136 citations


Journal ArticleDOI
TL;DR: In this article, the authors used the Bitter technique to observe magnetization distribution in the Co-Cr medium, and the transition of magnetization was directly observed on the top and bottom surfaces of the film.
Abstract: The extremely high resolution properties in a perpendicular magnetic recording system were studied with a recently developed Co-Cr film medium. Bitter technique was used to observe magnetization distribution in the medium, and the transition of magnetization was directly observed on the top and the bottom surfaces of the film. It was proved that an ideal perpendicular magnetization mode, having a very narrow transition width, takes place even in a high recording density over 40 kBPI. From the angular variation of H c and the micro-structure of the Co-Cr film, it was concluded that the high recording resolution of the film results from the fine columnar particles which show the rotational mechanism of magnetization reversal accompanied by a perpendicular magnetocrystalline anisotropy. The Co-Cr film was also found to be superior in perpendicular anisotropy to any other Co-M films studied here in.

116 citations



Journal ArticleDOI
TL;DR: The present state of understanding of the dynamics of magnetic domain walls and magnetic bubbles is reviewed in this paper, where the theory of domain wall motion for the linear and non-linear regions is outlined.
Abstract: The present state of understanding of the dynamics of magnetic domain walls and magnetic bubbles is reviewed The theory of domain wall motion for the linear and non-linear regions is outlined Experimental techniques for straight walls and magnetic bubbles are discussed An extensive comparison between theory and experiment is made Topics included are peak and saturation velocities, mobility, inertial effects and overshoot, hard bubbles, wall states and state transformations in magnetic bubbles Origins of wall damping are also discussed

115 citations


Journal ArticleDOI
TL;DR: The first ab initio self-consistent spin-polarized energy-band study of a ferromagnetic transition-metal film [Ni(001) was performed by as discussed by the authors.
Abstract: Results are presented of the first ab initio self-consistent spin-polarized energy-band study of a ferromagnetic transition-metal film [Ni(001)] that is thick enough (nine layers) to accurately determine the energy dispersion and spatial character of surface states and their effects on the surface spin polarization, surface magnetic moments, and average exchange splittings. Band structures and surface states, layer density of states, and charge and spin densities are presented and used to discuss a number of experiments. We find no evidence for magnetically "dead layers" on Ni(001) surfaces. The surface-layer magnetic spin moment is reduced by 20% from the center-layer magnetic moment (which has the bulk value) due to a majority-spin $d$-hole surface state at $\overline{M}$ which lies just above the Fermi energy.

111 citations


Journal ArticleDOI
TL;DR: In this paper, a spin-fluctuation theory was applied to iron and nickel for a discussion of their magnetic and thermodynamical properties at finite temperatures with a slight extension including the effect of charge fields within the steepest-descent approximation.
Abstract: A spin-fluctuation theory developed previously by the present author is applied to iron and nickel for a discussion of their magnetic and thermodynamical properties at finite temperatures with a slight extension including the effect of charge fields within the steepest-descent approximation. The Curie temperature, the average magnetization, the amplitude of local magnetic moments, the spin susceptibility and the specific heat are calculated, which are in qualitatively, or semi-quantitatively good agreement with experimental data.

Journal ArticleDOI
TL;DR: In this article, the magnetic reflection data was interpreted satisfactorily by considering a triangular spin structure of helically modulated ferromagnetic chains: the magnetic moments lie in the c-plane and rotate by 5.1±0.1° along the chain or the axis, while the moments rotate by 120° in the plane.
Abstract: Neutron diffraction measurements were made on single crystals of CsCuCl 3 . The sense of Cu 2+ ion helix was found from nuclear reflections to be predominantly right-handed. The magnetic reflection data could be interpreted satisfactorily by considering a triangular spin structure of helically modulated ferromagnetic chains: The magnetic moments lie in the c-plane and rotate by 5.1±0.1° along the chain or the c-axis, while the moments rotate by 120° in the c-plane. The magnitude of the magnetic moment is 0.58±0.01 µ B at 4.2 K. The critical exponent of the magnetization, β was found to be 0.358±0.015 around the Neel temperature, 10.70±0.05 K. We present a model that the helical modulation along the c-axis is caused by the antisymmetric exchange (Dzyaloshinsky-Moriya) interaction characteristic of the crystal symmetry of CsCuCl 3 . The model predicts a right-handed magnetic helix in the present case.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed an iterative method for the inversion of magnetic anomalies using a three-dimensional (3D) distribution of magnetized rectangular blocks, where the top and bottom surfaces of each of the blocks were adjusted in a least-squares sense to minimize the difference between observed and calculated field values.
Abstract: The height of the observation surface above a magnetized region primarily determines the critical dimension of the smallest inhomogeneity in magnetization that can be resolved from magnetic survey data. When a rectangular block is smaller in size than this critical dimension, it appears homogeneously magnetized in the observed magnetic field. This consideration leads to the selection of a unit rectangular block of suitable dimensions with homogeneous magnetization. The magnetized region creating the anomalous field values in the area of observation can, therefore, be broken up into several blocks having different magnetizations, each block being equal in size and uniformly magnetized.The iterative method described here assumes initially that the anomalous field values are caused by a three-dimensional (3-D) distribution of magnetized rectangular blocks. The optimum orientation of these blocks with respect to geographic north is then determined. This orientation is particularly insensitive to adjustments in the dimensions of the blocks. The top and bottom surfaces of each of the blocks in one or more layers are adjusted in a least-squares sense to minimize the difference between observed and calculated field values. A method is also described for constraining the magnetization vector of each block to lie within a specified angle of the normal or reversed direction of the geomagnetic field vector. The procedure for analysis of data can also be extended to the case of anomalies over a draped surface. At the conclusion of the iterations, a 3-D distribution of magnetization is generated to delineate the magnetized region responsible for the observed anomalous magnetic field. Examples including model and aeromagnetic data are provided to demonstrate the usefulness of a generalized multibody model for inversion of magnetic anomalies.

Journal ArticleDOI
TL;DR: The magnetization curves of the S = 1/2 proteins were analysed and it is shown that it is possible to make estimates of the ground-state g-factors even in the presence of rhombic anisotropy, provided that some knowledge of the polarizations of the electronic transitions is available.
Abstract: The magnetic-circular-dichroism (m.c.d.) spectra of methymyoglobin cyanide and oxidized horse heart cytochrome c were measured in the region of the Soret band over a range of temperatures from 1.5 to 50 K and in fields from 0 to 5T. A similar study has been made with reduced bovine heart cytochrome c oxidase, which contains one high-spin ferrous haem, namely a3. M.c.d. magnetization curves characteristic of an isolated Kramer's ground state with spin S = 1/2. These curves contrast with the magnetization curve of the high-spin ferrous haem with spin S = 2. The electronic ground state of the latter compound contains zero-field components that are thermally accessible over the temperature range of the experiment. Hence the magnetization curves are a complex nested set. The magnetization curves of the S = 1/2 proteins were analysed and it is shown that it is possible to make estimates of the ground-state g-factors even in the presence of rhombic anisotropy, provided that some knowledge of the polarizations of the electronic transitions is available. The striking difference between the m.c.d. magnetization curves of a simple S = 1/2 paramagnet and magnetically complex ground state should prove extremely useful when m.c.d. spectroscopy is sued to probe the magentic properties of metal centres in proteins, and should have wide application beyond the field of haemoproteins.

Journal ArticleDOI
TL;DR: In this article, a model based on Monte Carlo methods has been used to investigate the effects of magnetostatic and repulsive interparticle interactions on the properties of a magnetic fluid.
Abstract: A model based on Monte Carlo methods has been used to investigate the effects of magnetostatic and repulsive interparticle interactions on the properties of a magnetic fluid. The model predicts the formation of open loop structures in the absence of a magnetic field, and long chains in the presence of large magnetic fields. The model also predicts that the initial susceptibility is reduced in the presence of interactions. These predictions are in agreement with experimental observations.

Journal ArticleDOI
TL;DR: In this article, a magnetic phase diagram for CeB6 has been proposed and the paramagnetic susceptibility has been analyzed by assuming appropriate values of crystal-field splitting and exchange interactions.


Journal ArticleDOI
TL;DR: A detailed investigation on the thermal expansion, magnetic properties and electrical resistance of rapidly quenched amorphous (Fe,Co,Ni)-Zr alloys has been undertaken in this article.
Abstract: A detailed investigation on the thermal expansion, magnetic properties and electrical resistance of rapidly quenched amorphous (Fe,Co,Ni)-Zr alloys has been undertaken. Magnetic properties of these alloys are reported separately in this conference. The thermal expansion curves exhibit typical invar characteristics below the Curie temperature due to positive spontaneous volume magnetostriction us similar to those for Fe-Ni crystalline invar alloys. The reduced magnetization decreases strongly with increasing temperature being analogous to the case of other amorphous invar alloys. Moreover, w s at 0 K and electrical resistance at room temperature and Liq. N 2 temperature increase in the invar region. Amorphous ternary alloys of (Fe,Co, Ni) 90 Zr 10 with about 72 at% Fe have the invar characteristics in a wide temperature range and in this composition range, the volume magnetostriction and electrical resistance show maximum values of about 1.5 × 10-2and 160 μΩcm respectively.

Journal ArticleDOI
06 Nov 1980-Nature
TL;DR: In this article, the authors reported domain observations of titanomagnetites in samples from Leg 49 of the Deep Sea Drilling Project (DSDP) and showed that a major contributor to pseudosingle-domain remanence is single domain re-manence of particles larger than the classical single-domain threshold size which fail to nucleate domain walls in this magnetization state.
Abstract: The stable carriers of the palaeomagnetic record in rocks are commonly fine grains of magnetite or titanomagnetite (Fe3–xTixO4) between 1 and 15 µm in diameter. The magnetic properties of these particles are therefore of interest to palaeomagnetists who must rely on them to preserve the Earth's magnetic field record over geological time. We report here domain observations of titanomagnetites in samples from Leg 49 of the Deep Sea Drilling Project. The results indicate that a major contributor to ‘pseudosingle-domain’ (PSD) saturation remanence is single domain remanence of particles larger than the classical single-domain threshold size which fail to nucleate domain walls in this magnetization state.

Journal ArticleDOI
TL;DR: In this paper, two ESR modes in CuMnNi spin-glass alloys are interpreted with a phenomenological theory incorporating an order parameter, remanent magnetization, and anisotropy energy.
Abstract: Two ESR modes in CuMnNi spin-glass alloys are observed. Both modes are interpreted with a phenomenological theory incorporating an order parameter, remanent magnetization, and anisotropy energy. From simultaneous magnetization and ESR measurements, it has been possible to deduce the temperature and concentration dependence of the anisotropy constant, which has interesting scaling properties. The angular dependence of the field-cooled ESR and magnetization data suggest the need for another order parameter which vanishes at ${T}_{g}$.

Journal ArticleDOI
06 Mar 1980-Nature
TL;DR: In this paper, an effect whereby an anisotropic magnetic material acquires a remanence on exposure to an alternating magnetic field was predicted from an analysis of the phenomenon of rotational remanent magnetisation (RRM).
Abstract: An effect whereby an anisotropic magnetic material acquires a remanence on exposure to an alternating magnetic field (a.f.) is predicted from an analysis of the phenomenon of rotational remanent magnetisation (RRM). The remanence, which is of gyromagnetic origin, is produced even when there is no relative rotation between sample and field and all constant fields have been eliminated. The effect is demonstrated in magnetic recording tape and, as well as having important implications for a.f. demagnetisation techniques, may be relevant to magnetic recording processes.

Journal ArticleDOI
TL;DR: In this article, the magnetic ordered phase of the CeIn3 compound is shown to be an antiferromagnetic one with a propagation vector ( 1 2, 1 2, 1 2 ) and a weak value of the magnetic moment 0.48±0.08 μB.

Journal ArticleDOI
TL;DR: It is shown that the minimum magnetic field required to produce observable effects is quite large, and for the best case, the rield required for a 10 percent reduction in conductivity is roughly 24 T.
Abstract: The effects of steady magnetic fields upon the conduction of a nerve impulse are considered. Microscopic chemical effects as well as those due to induced fields are ignored. Arguing from an analysis of transport properties, we show that the minimum magnetic field required to produce observable effects is quite large. For the best case, the rield required to produce a 10 percent reduction in conductivity is roughly 24 T.

Journal ArticleDOI
TL;DR: The hexagonal ferrite W has a saturation magnetization about 10% higher than the widely used permanent magnet material M=BaFe3+12O19 and the anisotropy field is about equal.
Abstract: The hexagonal ferrite W=BaFe2+2Fe3+16O27 has a saturation magnetization about 10% higher than the widely used permanent‐magnet material M=BaFe3+12O19 and the anisotropy field is about equal. This opens up the possibility of using W as a permanent‐magnet material with a higher remanence Br and energy product BHm. This paper describes the sintering of W having a slight deviation from the stoichiometric composition and containing a trace of SiO2 at, e.g., 1220 °C in a reducing atmosphere to 92–95% of the x‐ray density and containing well‐oriented grains of 2–8 μm. Samples with coercive forces Hc=1.5–2.1, Br=4.4–4.7, and BHm=3.7–4.3 (B in kG, H in kOe) were obtained, which may be compared with Hc=2.1, Br=4.0, and BHm=3.4 found from our own measurements on high‐quality commercial M. We found surprisingly that the pickup of a trace iron during grinding increases the sintering density considerably, and this is therefore essential for the preparation of useful material.

Journal ArticleDOI
TL;DR: In this article, the magnetostriction constant and saturation magnetization at room temperature were measured for iron-based amorphous alloys containing various kinds of metalloid and metal atoms, except Co and Ni.
Abstract: The magnetostriction constant and saturation magnetization at room temperature are measured for iron‐based amorphous alloys containing various kinds of metalloid and metal atoms, except Co and Ni. The data show that the magnetostriction constant is proportional to the square of the saturation magnetization for these alloys.

Journal ArticleDOI
TL;DR: In this paper, the critical properties of a line of transitions between a spinglass and a ferromagnet have been determined for a series of amorphous Fe-Mn alloys.
Abstract: The critical properties of a line of transitions between a spin-glass and a ferromagnet have been determined for a series of amorphous Fe-Mn alloys. Detailed scaling analysis of the magnetization leads to the conclusion that the transition is continuous and similar to the Curie transition. The values of the critical exponents are given for the first time.

Journal ArticleDOI
TL;DR: The Fe2+ and the spin on the quinone in reduced reaction centers were found to be coupled with an exchange interaction 0 less than /J/ less than 1 cm-1, implying that quin one is most likely not a ligand of Fe.

Journal ArticleDOI
TL;DR: In this paper, the exchange magnetic moments are investigated by adopting a phenomenological approach and a field theoretical model, and their contributions for nuclei with a particle or hole outside a closed shell are estimated in terms of corrections of gyromagnetic factors.

Journal ArticleDOI
TL;DR: In this paper, it was shown that a large electrostatic potential difference must exist along the magnetic field lines under very general conditions, as a direct consequence of the interaction between a hot plasma and the Earth's magnetic field.

Journal ArticleDOI
TL;DR: In this paper, the POGO magnetic anomaly field measured between 400 and 700 km elevation over Australia by means of the equivalent source technique is modeled by using magnetic dipole moments computed for a latitude-longitude array of dipole sources on the earth's surface.