Magnetic field measurement apparatus

Claim 1

A magnetic field measurement apparatus comprising a magneto-optic transducer that has a polarizer, an analyzer, and a magneto-optic element made of a Bi-substituted rare-earth iron garnet crystal which is represented by the general formula Bi x Gd y Y 3- (x+y) Fe 5 O 12 (1.0≦x≦1.4; 0.1≦y≦0.7) and placed between the polarizer and the analyzer which have polarization directions different from each other, wherein the difference between the variation in the Faraday rotation angle of said crystal with temperature and the change in the saturation magnetization of said crystal with temperature is not more than ±0.025% /deg; light transmission paths that are provided on both sides of the magneto-optic transducer; a light generating means that supplies light to the light transmitting path; a light detecting means that detects the optical output power generated by the incident light that has passed through the magneto-optic transducer so as to convert the optical output power into electric signals; and an electric circuit that processes the electric signals fed from the light detecting means, wherein the magneto-optic transducer in a magnetic field is placed into the magnetic field to be measured to thereby determine the intensity of the magnetic field.