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The magnetization measurement of systems with the nominal formula (R = Eu, Gd, Tb, Y) has been made. It has been found that and are weak ferromagnets of Dzialoshinsky - Moriya type whereas is an antiferromagnet. The substitution of manganese ions by cobalt ones leads to the appearance of different magnetic states: cluster-spin-glass-like , inhomogeneous ferromagnets with well defined Curie temperatures and again a spin glass state . Spontaneous magnetizations and Curie temperatures reach maxima for compounds with x = 0.5. External magnetic field induces a metamagnetic transition in (R = Gd, Tb, Y). The transition becomes irreversible at low temperature in the Tb- and Y-based compounds. The annealing in vacuum of leads to the increase of the Curie temperature and to the appearance of a metamagnetic transition for the compound. The metamagnetic behaviour is interpreted taking into account the ionic ordering of and ions and possible 3d-orbital ordering in the sublattice.

Transport and magnetic properties of have been studied to construct the magnetic phase diagram. is found to be a weak ferromagnet with K. Anomalous magnetic behaviour of x = 0 and x = 0.1 compositions is attributed to the Nd-sublattice magnetic contribution. Materials with and are suggested to be mixtures of antiferromagnetic and ferromagnetic states. The inhomogeneous ferromagnets exhibit the giant magnetoresistance effect without the temperature-induced metal-insulator transition. The results are discussed in terms of the superexchange interaction model proposed by Goodenough.

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