Co magnetism and related phenomena in the Er(Co1-xSix)2 compounds

Results of magnetic, transport and dilatometric studies of the Er(Co1-xSix)2 compounds (for x≤0.15) in ambient and elevated pressures are presented. The Si substitution for Co yields a dramatic increase of TC although the room-temperature lattice volume does not change. The first-order magnetic phase transition at TC observed in ErCo2 persists for x≤0.075. The large resistivity drop observed just below TC and the negative magnetoresistance accompanying the field-induced metamagnetic transition above TC are attributed to Fermi surface reconstruction and to quenching of Co 3d spin fluctuations due to Co moment formation. Formation of the Co magnetic moment is reflected also in a pronounced lattice expansion. The resistivity, magnetoresistance and thermal expansion anomalies are progressively reduced with increasing x (and also with external pressure), which can be conceived with a progressively reduced Co moment. Application of external hydrostatic pressure causes reduction of TC at a rate ∂ ln TC/∂p∝-30 Mbar-1 in all the studied compounds. (orig.)