Introduction

Fascinating physical properties of lanthanide metals turned attention to their alloys, particularly those with transition metals and with elements of the fourth and fifth group of the Mendeleyev Table. Microscopic models of magnetic moment interactions operating in cerium pnictides have been proposed also. It has been observed in experiments that magnetic structures are stable in the presence of strong external magnetic fields or pressures and fully confirm the necessity of considering the above interactions. In the compounds showing either Kondo or mixed valency effects, this gap becomes smaller. The ternary systems with the crystal structure of ThCr2Si2 type attracted particular attention during the last few years because all of the most interesting properties which have been observed earlier in binary phases are shown by these phases, including mixed valence, Kondo lattice, and heavy fermion effects.