The energy crisis and critical need of advanced materials for engineering, pharmaceutical, and medical applications are calling for the development of new materials to response quickly and efficiently to such demand. For such imperative request, the fundamental understanding of materials, the origin of the properties in correlation with structure could be the main pathway toward the successful design and discovery. The principle of homologous series has been successful in creating new materials with control of specific module in the structure, to improve the electronic, magnetic and optical properties [1, 2]. For example, we can create and manipulate cooperatively in within the same crystal lattice of complex transition metal chalcogenide, ferromagnetism and semiconductivity, two properties difficult to combine in a conventional inorganic compound. However, ferromagnetic semiconductors are very attractive and might result in new physical phenomena and novel applications such as spintronic that has the particularities to use both the charge and the spin of electron to process and store information [3, 4]. In this talk, we will discuss my recent work using that principle of homologous series to develop a model of high Curie temperature ferromagnetic semiconductors using the complex metal chalcogenides. We will mainly focus on my recent discovery of both FeSb2Se4 [5] a p-type and FeBi2Se4 [6] n-type ferromagnetic semiconducting materials with a Curie temperature of 450K [5, 6] that can be tuned through doping with Sn or In.

_{Reference: [1] R. J. Cava, J.Am.Ceram.Soc. 83 [1] 5-28(2000) [2] A. Mrotzek and M. G. Kanatzidis, Accoun. Chem. Re. 36(2) 111-119 (2003) [3] H.Ohno et al. Appl. Phys. Lett. 69, 363-365 (1996) [4] M. N. Leuenberger et al. Nature, 410, 789-793 (2001) [5] H. Djieutedjeu et al. Angew. Chem. Int. Ed. 49, 9977-9981 (2010) [6] K. G. S. Ranmohotti et al. J. Am. Chem. Soc. 137, 691-698 [7] H. Djieutedjeu et al. Manuscript in progress.}