Mn-Znフェライト単結晶の初透磁率に及ぼす応力効果の異方性

Abstract

Manganese Zinc ferrite single crystals have been widely used for making video cassette recorder (VCR) heads. The initial permeability is one index relating to the performance of magnetic heads. It was known that the initial permeability of the crystals decreased as a function of residual stresses left after machining of the magnetic heads. At that time, most of the crystals were grown in the Bridgman furnace, so that compositional segregation could not be avoided and no research work was systematically carried out on the relationship between anisotropic stress effects and initial permeability of the crystals. For the tensile and compressive samples we used very uniform single crystals of less than 0.1mol% compositional segregation, produced by solid phase reaction. The variously orientated crystal samples, shaped like picture frames, were cut by ultrasonic machining and etched more than 20μm deep by a heat phosphoric acid to remove residual stresses. The initial permeability was measured during tensile and compressive tests as a parameter of frequency from 100kHz to 100MHz, in a temperature-controlled silicon oil bath. The initial permeability of the crystal samples under uniaxial stress was also obtained theoretically by the magnetocrystalline anisotropy energy due to the rotation magnetization. It was found that the initial permeability at 50MHz might be improved by more than 10dB by applying the tensile stress of 25MPa at <100> direction. This phenomenon may be applied to other applications.