Muon spin rotation of the relaxation of Ho and Er magnetic moments in high-T(sub c) 1-2-3 compounds

High-temperature superconductors HoBa2Cu3O(sub 7-delta) (T sub c= 93 K), Ho(sub 0.5)Y(sub 0.5)Ba2Cu3O(sub 7-delta) (T sub c approx equal 93 K) and ErBa2Cu3O(sub 7-delta) (T sub c approx equal 95 K) were investigated by zero-field mu SR-technique. The muon spin depolarization rate connected with the fluctuation frequency of rare-earth ion magnetic moments was measured. It was found that the samples with holmium show fast increase of the muon spin depolarization rate at the temperatures below 20 K while in ErBa2Cu3O(sub 7-delta), the depolarization rate remains low in the whole studied temperature region (4.2 - 270 K). The sharp difference between the behaviours of the muon spin depolarization rate may be explained by the difference between the ground state of Ho(exp 3+) and Er(exp 3+) ions in the crystalline field of the lattice.