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

Abstract

We report a study of the effect of hydrostatic pressure (P) on the Griffiths-like phase in selected compounds of the R5(SixGe1 ? x)4 family of alloys (Tb4.925La0.075Si2Ge2 and Gd5Ge4) which present either the Gd5Si2Ge2-type (monoclinic, M) or the Sm5Ge4-type [orthorhombic-II, O(II)] structural phases at room temperature. The downward deviation in the inverse low-field dc susceptibility ??1 dc from the Curie-Weiss law below a characteristic temperature TG 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 Dy5Si3Ge 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 ?0.5 between the dT G/dP and the pressure coefficient of long-range magnetic ordering temperatures, dTC,N/dP (TC, ferromagnetic; TN , antiferromagnetic), is found in all the studied compounds.