Nanogranular structure material and method for producing same

A nanogranular thin film comprising:

• a matrix formed of a fluorine compound having a composition represented by M-F;
• and
• metal oxide nanoparticles dispersed in the matrix and having a composition represented by L-O,
• the nanogranular thin film having a composition represented by L-M-F—O,
• wherein L is at least one element selected from the group consisting of Fe, Co, and Ni, M is at least one element selected from the group consisting of Li, Be, Mg, Al, Si, Ca, Sr, Ba, Bi, and rare earth elements, F is fluorine, O is oxygen, and an atomic ratio of L is within a range of 0.03 to 0.50, an atomic ratio of M is within a range of 0.03 to 0.30, an atomic ratio of F is within a range of 0.06 to 0.65, and an atomic ratio of O is within a range of 0.04 to 0.50, and
• wherein an absolute value of a Faraday rotation angle for light in a wavelength region of 500 to 680 nm is within a range of 0.1 deg/μm or more.