Decoupling of the magnetic ordering of the rare-earth and the Co sublattice in Er1-xYxCo2 compounds driven by substitution or pressure

The thermodynamic and transport properties of the Er1-xYxCo2 system were st udied in the concentration range 0.0 less than or equal to x less than or e qual to 1.0: In this system, the first-order magnetic phase transition obse rved in ErCo2 at T-C = 32 K is related to the itinerant electron metamagnet ism of the d subsystem (Co sublattice) driven by the onset of magnetic orde ring within the Er sublattice. By employing magnetic, specific heat, therma l expansion, and resistivity measurements we show that in a limited concent ration range x(cr') < x < x(cr) and pressure P-cr' < P < P-cr the itinerant Co sublattice orders magnetically at T-C(Co), which is lower than T-C(R) o f the Er sublattice. This is referred either to a weakening of the effectiv e molecular field acting on the Co sites owing to the yttrium subsititution or to a pressure-driven increase of the critical field necessary to induce a magnetic moment on the Co sites. On further increasing the yttrium conce ntration or the pressure only the Er sublattice exhibits long-range order. The theoretical calculations within the molecular field approximation are i n agreement with the experimental magnetic x-T phase diagram of the Er1-xYx Co2 system and confirm the effect of a separate ordering of the magnetic su blattices with reasonable parameters used for the intrasublattice Er-Er and intersublattice Er-Co exchange interactions. A field-induced collapse of t he Co moment, inverse itinerant electron metamagnetism, is well observable by magnetoresistance measurements at appropriate Values of concentration an d external pressure. The existence of itinerant electron metamagnetism in t he Co sublattice is found to be limited in temperature by T-0, a characteri stic temperature which is sensitive to substitution and pressure.