Magneto-optical element and magnetic field measurement apparatus

A magnetic field measurement instrument, comprising:

• a magneto-optical transducer including a polarizer, an analyzer and a magneto-optical element placed between the polarizer and the analyzer, the magneto-optical element being made of a bismuth-substitution rare earth iron garnet crystal of a chemical formula
• (Bi.sub.X Gd.sub.Y R.sub.Z Y.sub.3-X-Y-Z)(Fe.sub.5-W Ga.sub.W)O.sub.12,
• wherein R designates an element selected among rare earth
• elements, wherein
• 0. 8.ltoreq.X.ltoreq.1.3,
• 0.1.ltoreq.Y.ltoreq.0.3,
• 0.1.ltoreq.Z.ltoreq.1.0
• and
• 0.3.ltoreq.W.ltoreq.0.8,
• the analyzer being provided so as to make the direction of transmitted light through the magneto-optical element different from that of the polarizer;
• a first optical transmission line connected via the polarizer at an end of the magneto-optical element of the magneto-optical transducer;
• a light source for generating light to the first optical transmission line;
• a second optical transmission line connected via the analyzer at the other end of the magneto-optical element of the magneto-optical transducer;
• an optical sensor for detecting an optical output from the second optical transmission line to convert to an electrical signal;
• and
• a signal processor for processing an electrical output signal from the optical sensor;
• wherein a magnetic field is measured by placing the magneto-optical converter in a magnetic field and by detecting a change in intensity of output light with the signal processor when the incident light transmits the magneto-optical transducer.