Metamagnetism of manganese subsystem in RMn2 intermetallic compounds

Results are presented of an investigation of the magnetic properties and crystal structure of intermetallic compounds RMn2 possessing a cubic structure C15 (R=Cd, Tb, Dy) or hexagonal structure C14, (R=Ho, Er, Tm). The study is carried out in the temperature range from 5.5 to 300 K. It is shown that whereas for R=Dy, Ho, Er, Tm the transition to the magnetically ordered state is a transition of the second kind, for R=Gd and Tb it is a transition of the first kind with a discontinuous increase in volume of the elementary unit (ΔV/V approximately 15x10-3 at 5.5 K). It is concluded that such behaviour of GdMn2 and TbMn2 is related to magnetic ordering of the manganese subsystem, which is of a metamagnetic nature. In other RMn2 compounds the exchange field acting op the manganese sUbsystem from the rare earth sublattice is smaller, and consequently the manganese sublattice does not become ordered. The results are compared with the behaviour of the 3d-subsystem in similar RM2 compounds in which M=Fe+ Co or Ni