Hans Hauser

Energetic model of ferromagnetic hysteresis

Calculations of a total energy function are used to describe a theory of hysteresis effects in crystalline, ferromagnetic materials. This model is applied on the cubic structure of FeSi crystals, which are oriented in a (110)[001] texture. The magnetic energy of the crystal is separated in reversible and irreversible parts: The reversible energy is expressed by magnetocrystalline anisotropy and shape anisotropy. They are responsible for the rotation of the domain magnetization at strong fields. At weak fields the reversible interaction of the domain wall motion with the stray fields of pinning centers (nonmagnetic inclusions, grain boundaries or inner strains) is described by a probability function of statistic domain behavior. The irreversible energy is caused by these pinning centers, too, and can be explained by the interaction losses of the magnetic moments in the Bloch wall with the crystal lattice during an irreversible Barkhausen jump. The energy of the applied field is added to these two parts and...

Energetic model of ferromagnetic hysteresis: Isotropic magnetization

The model is based on considerations of energy balance and statistical domain behavior. The parameters are related to macroscopic hysteresis features such as coercivity, initial susceptibility, saturation, and remanence and identification strategies are presented for static and dynamic magnetization processes. Furthermore, the model parameters are related to spontaneous magnetization, magnetocrystalline anisotropy, magnetostriction, and microstructure geometry which assist in the interpretation of the hysteresis dependence on stress, temperature, and direction of magnetization. Examples and predictions are the magnetization reversal in low dimensional structures, stress demagnetization, temporary decay of magnetization, Barkhausen noise, and the behavior of materials with multiple phases. Finally, the fictitious statistical domains (or unit magnetization reversals) are related to the magnetic spin moments, which enables a quantum-mechanical interpretation of the model.

Fast latching type optical switch

A magneto-optical latching switch with a yttrium orthoferrite optical rotator is described. The crystal remains in a given magnetic state for unlimited duration without energy supply. The response time is about 20 ns and the aperture of the optical rotator is 350 μm.

Magneto-optical current sensors of high bandwidth

A new current transformer is described by means of new results concerning the domain wall excitation in orthoferrites. The measured parameter is the geometrical position of the boundary between domains with opposite magnetizations. In a wide frequency band, including DC currents, the measurement results are a linear function of the measured current due to the very high domain wall velocity. They are not affected by temperature changes and mechanical factors.

Magnetooptic switch based on domain wall motion in orthoferrites

A prototype of an optical switch based on Faraday rotation in yttrium orthoferrite crystals is developed. The switch is of latching type and has an operating time below 100 ns. Integrated arrays of switches are feasible due to the dimensions of the optical rotator of less than 3 mm/sup 3/.

Wirelessly interrogable magnetic field sensor utilizing giant magneto-impedance effect and surface acoustic wave devices

A micro-magnetic field sensor is developed using the giant magneto-impedance (GMI) effect in a 30 /spl mu/m diameter amorphous FeCoSiBNd wire of zero magnetostriction. Surface Acoustic Wave (SAW) devices are described as passive, radio requestable sensor devices. A new type employs the electrical load of the SAW device by the impedance of conventional sensors. In order to develop a wirelessly interrogable magnetic field sensor, the combination of GMI sensors and SAW transponders is discussed by several measurements. The device shows a relative signal sensitivity of 80 dB/T at low magnetic flux density B<30 mT, quick response (/spl ges/40 MHz bandwidth), and a high-temperature stability.

Magnetization reversal in an energetic hysteresis model

Abstract In the energetic model the magnetic state of the material is represented by the minima of the total energy function. The model describes hysteretic curves from the demagnetized state up to saturation. At an arbitrary point of magnetization reversal, however, the distribution of the distances between domain walls and pinning centers has to be considered with respect to the magnetic history, which is important for the calculation of minor hysteresis loops.

Magneto-optical current sensor by domain wall motion in orthoferrites

A brief review of the latest developments on optical current measurements based on the Faraday effect is presented. In all existing magneto-optical current transformers, the main measured parameter is the polarization state of the light transmitted by a sensor element. A new transformer is described by means of new results concerning the domain wall excitation. The measured parameter is the geometrical position of the boundary between domains with opposite magnetizations. In a wide frequency band, including DC currents, the measurement results are a linear function of the measured current. They are not affected by temperature changes and mechanical factors.

The effect of mechanical stress on the magnetization curves of Ni- and FeSi-single crystals at strong fields

The spatial distribution of the total energy is used to determine the magnetic behavior of ferromagnetic single crystals. For a single ferromagnetic domain there exists only a homogeneous magnetization the direction of which must correspond to a minimum energy direction. Magnetization curves are calculated by observing the stable positions of the magnetization under the application of strong magnetic fields. These magnetization curves show significant variations under different states of mechanical stress for FeSi and Ni crystals. >

Energetic model of ferromagnetic hysteresis 2: Magnetization calculations of (110)[001] FeSi sheets by statistic domain behavior

An energetic model of statistic domain behavior is applied on the magnetization process of grain oriented FeSi‐steel sheets. The physical constants of the model are derived from anisotropic energy contributions, initial susceptibility, coercivity, and saturation magnetization. Calculated in the [100], [011], and [111] – directions, the hysteretic magnetization curves indicate good agreement with measurements from the demagnetized state up to saturation. The better correspondence between theory and experiments at weak fields is achieved by using realistic initial occupation probabilities for the domain structure. This assumption leads to complex mutual dependencies of the statistic domain’s volume fractions, which have not been considered in previous works.