MAGNETIC-BEHAVIOR OF GAMMA-PHASE HYDRIDES RCO3H-SIMILAR-TO-4 IN HIGH MAGNETIC-FIELDS

High-field magnetization measurements have been carried out for single -crystal gamma-phase hydrides RCo3H(approximately 4) with R = Th and D y and for powder samples with R = Nd and Gd. The results indicate that these gamma-phase hydrides with R = Y, Ho and Er become antiferromagn etic except for R = Gd at low temperatures due to the appearance of a negative Co-Co intersublattice interaction. A metamagnetic transition of the Co-sublattice magnetization occurs from the antiferromagnetic t o the forced ferromagnetic state if the field is applied along the c-a xis. GdCo3H(approximately 4), being ferrimagnetic at low temperatures, becomes antiferromagnetic above 32 K. The significant weakening of th e R-Co interaction due to hydrogenation leads to a Neel temperature of about 200 K in all hydrides and an almost independent behaviour of th e R and Co sublattices in the compounds with R = Nd, Ho and Er. The ro le of the R-Co interaction in the magnetic behaviour of the hydrides i s discussed.