Magnetism in HoCo2 and ErCo2 under high pressure

Temperature dependencies of the electrical resistivity rho (T) was studied on HoCo2 and ErCo2 under the hydrostatic pressure up to 8 GPa, At ambient pressure the resistivity drops dramatically at the Curie temperature T-C (=78 and 33 K, respectively) as a result of the Co 3d-band moment formation in these two RECo2 compounds (RE=rare earth), The applied pressure P affects considerably both, T-C and the rho (T) anomaly in the vicinity of T-C. Initially, the value of T-C becomes reduced linearly with increasing P up to approximately 1.5 Gpa. The measurements in pressure beyond 1.5 GPa, however, reveal that the real T-C vs. P dependence gradually deviates from the initial linear trend. Simultaneously, the rho (T) drop at T-C becomes gradually reduced and vanishes for higher pressures (P>4 GPa) where T-C becomes nearly pressure independent. We conclude that these phenomena reflect the pressure induced suppression of Co metamagnetism. This behavior will be discussed within a model assuming that for P > P-c the projected Co-3d density of states in the vicinity of E-p decreases critically and the RE-Go-RE exchange channel becomes ineffective to induce the metamagnetic splitting of the Co 3d majority and minority subbands. This scenario is corroborated by results of ah initio electronic structure calculations. (C) 2001 Elsevier Science B.V. All rights reserved.