Details

Autor(en) / Beteiligte

• Dionne, Gerald F.

Titel

Electromagnetic Properties

Ist Teil von

• Magnetic Oxides, 2009, p.273-342

Ort / Verlag

Boston, MA: Springer US

Erscheinungsjahr

2009

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• In the previous chapters, the emphasis is placed on the electronic origins of static magnetism in electrically insulating compounds, beginning with isolated moments of transition metal ions coupled paramagnetically and progressing to the various spontaneous magnetic systems. Apart from occasional references to their application in magnetic recording by the switching of magnetic domains and their use as permanent magnets in applications requiring electrical insulation, few indications are given that relate to their important applications in time-varying magnetic fields and as electromagnetic transmission media. The most common usage of ferrimagnetism is for high permeability cores of inductors and transformers that typically operate at audio frequencies, i.e., below 20 kHz, and most commonly 60 Hz for power applications. Despite their generally lower magnetization when compared with ferromagnetic metal alloys, the reduction of eddy current losses makes these oxide materials an attractive alternative to laminated magnetic steel in many cases. In the partially magnetized state, the frequency dependence of the permeability results from three causes (1) magnetization rotation, (2) magnetic domain wall resonance, and (3) gyromagnetic resonance within individual domains. The former two arise from longitudinal coupling between the alternating magnetic field and the domain magnetization vectors, and usually occur in the frequency range below 1 GHz. The third is the same transverse interaction effect that is exploited in magnetic resonance, where a magnetic field renders the material single domain. It can set in below 1 GHz, usually after the longitudinal permeability has been reduced to small values by damping effects, and can cause large absorption over a band that reaches to several GHz, depending on the anisotropy and geometrical demagnetizing fields.