Abstract: A material for use in a 1.5 .mu.m wide-band optical isolator, includes a bismuth-substituted terbium-iron garnet single crystal having a composition of Bi.sub.x Tb.sub.3-x Fe.sub.5 O.sub.12 in which x is 0.35 to 0.45. This bismuth-substituted terbium-iron garnet single crystal is grown by a solid phase reaction. A process for producing such a material is also disclosed.

Abstract: A method of manufacturing ferrite crystals such as single crystal bodies and polycrystal bodies with garnet structure is disclosed, which includes the steps of effecting a composition controlling for raw powders, forming raw powders, sintering formed bodies and effecting hot isostatic press treatment for sintered bodies. Also, a method of producing ferrite powders preferably used for the ferrite crystal manufacturing method mentioned above.The thus obtained ferrite crystal bodies with garnet structure show good magnetooptical properties such as light transmissivity, Faraday rotation angle and Verdet constant, and are preferably used for magnetooptical elements such as optical isolators and optical magnetic field sensors etc.

Abstract: A high sensitivity optomagnetical sensor comprising a light source, a magnetic field-detecting section, a light-receiving section for receiving light emitted from the light source through the magnetic field-detecting section, a measurement-controlling section for controlling the light source, the magnetic field-detecting section, and the light-receiving section, and for measuring an intensity of light received by the light-receiving section, and light transmission paths using optical fibers for optically connecting the light-source section and the magnetic field-detecting section and optically connecting the magnetic field-detecting section and the light-receiving section. The magnetic field-detecting section is constituted by a polarizer, an analyzer and a magnetooptical element arranged between the polarizer and the analyzer. A garnet type ferrite polycrystal is used as a magnetooptical element of the sensor. The ferrite polycrystal has a Verdet constant of not less than 1 deg/cm.