Titanium dioxide (TiO2) is a material that has been put to practical use for the photodecomposition of water and the decomposition and removal of a hazardous substance, and further improvements in the photocatalytic activity of titanium dioxide are now demanded from the standpoint of energy and environmental problems.
Also, as semiconductors, Si and GaAs are now in the mainstream. While these conventional semiconductors are materials capable of realizing electrical functions by carrier control, or photoelectric functions as in laser diodes and photodiodes, there has been made available no semiconductor material that can realize a magnetic function as with a magnetic memory. Titanium dioxide is a semiconductor crystal which with its band gap in the ultraviolet range has a photoelectric function. If given a magnetic function anew and left to continue to possess the photoelectric function, then this material could become a semiconductor material that is capable of realizing an optical, an electrical and a magnetic function all together.
A material so far called a magnet is a substance that does not transmit a visible light and hence is black. If a transparent magnet is realized, then such magnets will unquestionably be useful over diverse fields of industry, not to speak of their good serviceability in paper clips.
By the way, the prior art where it is designed to impart magnetism to a transparent insulator includes a technique illustrated in FIG. 14. A powder of a nonmagnetic insulator, such as Al2O3, transparent to a visible light is mixed with particles of a magnetic metal such as Co or the like, and the mixture is then sintered. In a transparent magnet so prepared, increasing the magnetic metal particles in amount brings about amorphization of the nonmagnetic insulator due to the presence of the magnetic metal particles, and let it lose its crystallinity, thus the transparency and insulating properties which the transparent insulator as the matrix originally possesses.
As a magnetic semiconductor there exists now a mixture of GaAs with Mn as well as a CdMnTe material, and there is indeed a material having a magnetic function and further an optical function as the Faraday rotation. But none of these conventional magnetic semiconductors is transparent to a visible light, however.
Thus, no semiconductor material has hitherto existed or been made available that is transparent to a visible light and possesses a magnetic function.
In view of the problems mentioned above, it is an object of the present invention to provide the titanium dioxide-cobalt magnetic film and the method of its manufacture, the titanium dioxide-cobalt magnetic film having a magnetic function added to, and without losing the crystallinity of titanium dioxide, and being usable as a semiconductor possessing an optical, an electrical and a magnetic function all in combination, and a transparent magnet as well.