An information recording medium having such a recording material layer on a substrate where reversible
phase change between electrically or optically detectable states can be caused by
electric energy or electromagnetic energy. The recording material forming the
recording layer is either a material having a
crystal structure including
lattice defects in one phase of the reversible
phase change or a material having a complex phase composed of a
crystal portion including a lattice defect in one phase of the reversible
phase change and an amorphous portion. Both portions contain a
common element. A part of the
lattice defects are filled with an element other than the element constituting the
crystal structure. The recording medium having a recording thin film exhibits little variation of the recording and
reproduction characteristics even after repetition of recording and
reproduction, excellent weatherability, strong resistance against composition variation, and easily controllable characteristics.