Temperature-compensated magnetic field measuring instrument

A measuring instrument of magnetic field comprising:

• a light source part;
• a magnetic filed sensing part including a magnetic material, said magnetic material being provided with a medium capable of exhibiting Faraday rotation, said medium having at least one thin magnetic garnet film, means for providing linearly-polarized light from said light source to be vertically indicent upon said at least one thin magnetic garnet film, said thin magnetic garnet film having a composition expressed by a general formula R.sub.3-x Q.sub.x (Fe.sub.5-y M.sub.y)O.sub.12 (where R is at least one element selected from a group consisting of Y, La, Lu, Ca, Sm and Bi, Q is at least one element selected from a group consisting of Gd, Eu, Er, Tb, Yb, Ho and Dy, M is at least one element selected from a group consisting of Ga, Al, Ge, Si, Sc, Mn, In, V and Cr, the value of x lies in a range expressed by a formula 0.1.ltoreq.x.ltoreq.3.0, and the value of y lies in range expressed by a formula 0.ltoreq.y.ltoreq.5.0) so as to provide temperature-compensation for said magnetic field measuring instrument, said thin magnetic garnet film being magnetized in a propagation direction of the linearly-polarized light;
• a measuring part for receiving and processing light from said magnetic field sensing part;
• and
• an optical transmission line for optically connecting said light source part, said magnetic field sensing part and said measuring part;
• whereby said temperature-compensated measuring instrument enables stable measurement of a magnetic field substantially independent of temperature variation.