Ferromagnetism, superconductivity and magnetoresistance of Y$_{9}$Co$_{7}$

Crystal structures and physical properties of Y$_{9}$Co$_{7}$ and the related compound Y$_{8}$Co$_{5}$ will be discussed. In both materials, the crystallographic units consist of trigonal prisms formed by yttrium atoms centered around a cobalt atom. However, superconductivity and ferromagnetism occur only in Y$_{9}$Co$_{7}$. Magnetic susceptibility measurements (Arrot's method) on Y$_{9}$Co$_{7}$ give a Curie temperature T$_{Curie}$ = 4.25K and specific heat measurement provide evidence for bulk superconductivity with T$_{SC}$= 2.6K. The very large residual resistance ratio (RRR=30) confirm the excellent quality of the samples. Results of magnetoresistance up to 35T obtained in National High Magnetic Field Laboratory (NHMFL) will be discussed. The electrical resistivity measured at a temperature of 1.8K exhibits three different regions: for the field H$<$H$_{C}$ the material is superconducting, for H$_{C} \quad <$ H $<$ 1T resistivity rapidly increases and then for H $>$ 1T magnetic field causes excellent linear response of rho(H).