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

Abstract

The thermodynamic and transport properties of the ${\mathrm{Er}}_{1-x}{\mathrm{Y}}_x{\mathrm{Co}}_2$ system were studied in the concentration range $0.0<~x<~\mathrm{1.0.}$ In this system, the first-order magnetic phase transition observed in ${\mathrm{ErCo}}_2$ at $T_{\mathrm{C}}=32\mathrm{}$ K is related to the itinerant electron metamagnetism of the d subsystem (Co sublattice) driven by the onset of magnetic ordering within the Er sublattice. By employing magnetic, specific heat, thermal expansion, and resistivity measurements we show that in a limited concentration range $x_{{\mathrm{cr}}^{\prime }}<x<\mathrm{}{x}_{\mathrm{cr}}$ and pressure $P_{{\mathrm{cr}}^{\prime }}<P<\mathrm{}{P}_{\mathrm{cr}}$ the itinerant Co sublattice orders magnetically at $T_{\mathrm{C}}^{\mathrm{Co}},$ which is lower than $T_{\mathrm{C}}^R$ of the Er sublattice. This is referred either to a weakening of the effective 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 concentration or the pressure only the Er sublattice exhibits long-range order. The theoretical calculations within the molecular field approximation are in agreement with the experimental magnetic x-$T$ phase diagram of the ${\mathrm{Er}}_{1-x}{\mathrm{Y}}_x{\mathrm{Co}}_2$ system and confirm the effect of a separate ordering of the magnetic sublattices with reasonable parameters used for the intrasublattice Er-Er and intersublattice Er-Co exchange interactions. A field-induced collapse of the Co moment, inverse itinerant electron metamagnetism, is well observable by magnetoresistance measurements at appropriate values of concentration and external pressure. The existence of itinerant electron metamagnetism in the Co sublattice is found to be limited in temperature by $T_0,$ a characteristic temperature which is sensitive to substitution and pressure.