Effects of hydrogen in solid solution upon the magnetic order in erbium

The magnetisation of polycrystalline Er and α ErHsub(x) solid solutions (O <= x <= 0.03) was measured between 4.2 and 200 K in applied fields 0.2 <=H<=55 kOe. A drop in the paramagnetic Cure temperature, thetasub(p), was observed from 40 K in Er to 31.5 K in ErHsub(x) (with no significant x dependence); a decrease of the antiferromagnetic and the helical transition temperatures, Tsub(N) and Tsub(H), with increasing x; an increase in the Curie temperature, Tsub(C), and in another critical point, Tsub(Cl), with increasing x; and a strong magnetic hardening of the solid solutions, with the appearance of an x-dependent critical field, Hsub(c) = 18, 16 and 13 kOe for x = 0.01, 0.02 and 0.03. The decrease in Tsub(N) and Tsub(H) is attributed to a weakening RKKY exchange interaction due to a pumping of conduction electrons by hydrogen. The other results are explained through an anisotropic magnetoelastic interaction of hydrogen atoms with the crystal field, leading to an opening-up of the top angle of the ferromagnetic cone structure thus turning the total moment towards the basal plane. (author)