Disclosed is a ferromagnetic alkali
chalcogen compound capable of providing a completely-spin-polarized transparent ferromagnetic material using an alkali
chalcogen compound having light-transparency, and a method of adjusting ferromagnetic properties thereof. The transparent ferromagnetic alkali
chalcogenide comprises an alkali
chalcogen compound which has an anti-
fluorite structure and contains at least one
metal element selected from a 3d
transition metal element group consisting of Ti, V, Cr, Mn, Fe, Co, Ni and Cu; a 4d
transition metal element group consisting of Zr, Nb, Mo, Tc, Ru and Rh; a 5d
transition metal element group consisting of Hf, Ta, W, Os, Re and Ir; and a
lanthanum-series rare-earth element group consisting of Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The selected
metal element is incorporated in the alkali chalcogen compound in the form of a
solid solution to provide a ferromagnetic characteristic thereto. The ferromagnetic properties are adjusted through control of valence states based, for example, on adjustment of a concentration of each of the
metal elements, selection of a combination of two or more of the metal elements, and / or addition of an
acceptor and a donor.