The magnetization, a.c. susceptibility, resistivity and magnetoresistance have been measured for the invariable-unit-cell-parameter Ho(Co1-xSix)2 compounds. The Si substitution for Co in HoCo2 yields a dramatic initial increase of TC, whereas the 3d magnetic moment is reduced. These findings may be attributed to the strong involvement of Si p states in the hierarchy of exchange interactions. The magnetic phase transition at TC is of first order for the compounds with x < 0.075. For these compounds, the coexistence of metamagnetism and the quenching of spin fluctuations at T > TC are provided.
