Pressure dependence of the Griffiths-like phase in 5:4 intermetallics

We report a study of the effect of hydrostatic pressure (P) on the Griffiths-like phase in selected compounds of the $R_5{({\mathrm{Si}}_x{\mathrm{Ge}}_1-x)}_4$ family of alloys (${\mathrm{Tb}}_{4.925}{\mathrm{La}}_{0.075}{\mathrm{Si}}_2{\mathrm{Ge}}_2$ and ${\mathrm{Gd}}_5{\mathrm{Ge}}_4$) which present either the ${\mathrm{Gd}}_5{\mathrm{Si}}_2{\mathrm{Ge}}_2$-type (monoclinic, M) or the ${\mathrm{Sm}}_5{\mathrm{Ge}}_4$-type [orthorhombic-II, O(II)] structural phases at room temperature. The downward deviation in the inverse low-field dc susceptibility ${\chi }_{dc}^{-1}$ from the Curie-Weiss law below a characteristic temperature $T_G$ indicates that the Griffiths-like phase exists at pressures up to 10 kbar. From the obtained T-P phase diagrams, the pressure coefficient of the Griffiths-like temperature, ${dT}_G/dP$, has been determined. These results are compared with those obtained in ${\mathrm{Dy}}_5{\mathrm{Si}}_3\mathrm{Ge}$ in a previous work. The ${dT}_G/dP$ coefficient is strongly dependent on the nature (first or second order) of the long-range order (FM or AFM) transition. This effect can be ascribed to a different structural character of the clusters within the Griffiths phase. A ratio of $\sim 0.5$ between the ${dT}_G/dP$ and the pressure coefficient of long-range magnetic ordering temperatures, ${dT}_{C,N}/dP$ ($T_C$, ferromagnetic; $T_N$, antiferromagnetic), is found in all the studied compounds.