Talk

Tuesday, May 10th, 2011

Speaker

Aphrodite Ktena

Affiliation

TEI Chalkidas, Greece

Title

Preisach formalism and applications in magnetic materials

Location

Department of Physics Bldg., Voutes, 3^rd floor Seminar Room

Time

12:00

Language

English

Abstract

The magnetization process is the result of complex interactions between the applied magnetic field and localized atomic magnetic moments as well as the long-range magnetostatic energy of the material. The evidence of this process at the macroscopic level is the hysteresis loop which is characteristic of a material under given measurement conditions. Hysteresis is a highly nonlinear input-output relationship where a given output corresponds to two inputs, depending on whether the input is decreasing or increasing. In magnetic hysteresis, input is the applied magnetic field, H, and output is the magnetization, M, or the magnetic induction, B. Hysteresis can be a blessing or a curse: highly desirable in storage and permanent magnet applications; major source of uncertainty in sensing and actuating. Several magnetization reversal mechanisms, eg domain wall movement, pinning, domain rotation, have been proposed in order to explain magnetic hysteresis, at the microscopic level. However, hysteresis modeling remains still a challenging task. At the macroscopic level, Preisach modeling is a popular approach because it lends itself to fast and efficient algorithms usable as stand-alone models or core models in self-consistent or FEM calculation. Preisach formalism postulates that the magnetization, M, of a material at a given field, H, is the aggregate response of hysteresis operators γ(α,β) weighed by a probability density function ρ(α,β) where α and β are the operators’ upper and lower switching fields. Classical Preisach Model is an inherently scalar model which can be modified to model vector processes introducing a vector hysteresis operator, such as the Stoner-Wolhfarth model of coherent rotation. The identification of the model consists in determining ρ(α,β), characteristic of a material, via minor or major loop measurements on a VSM or other hysteresiograph. Usually, the major loop measurement, and the material’s macroscopic parameters obtained from it, ie remanence, M_r, saturation, M_s, coercivity H_c and coercivity squareness, χ(Hc) = dM/dH|_Hc, suffices. Applications of the Preisach model for the modeling of hysteresis in ferromagnets, anti-ferromagnetically coupled thin films, and shape memory alloys demonstrate the range of its applications and its ‘tuning-in’ capabilities. Correlating Preisach model parameters to microstructural parameters of the material, such as grain size, dislocation density et al, is expected to contribute to the design and development of novel materials and techniques, such as non-destructive testing.

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