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Griffiths-like phase and magnetic correlations under pressure of magnetocaloric R5(SixGe1-x)4 (R = Dy, Tb and Gd)

AutorMarcano, N.; Algarabel, Pedro A. ; Rodríguez Fernández, J.; Herrero-Albillos, Julia; Magen, Cesar; Araújo, J. P.; Pereira, A. M.; Belo, J. H.
Fecha de publicación2016
CitaciónSCTE (2016)
ResumenThe discovery of the giant magnetocaloric effect in Gd5Si2Ge2 has attracted a strong interest in the study of other R5(SiGe)4-type (R= rare earth) compounds in order to understand the relationship between their structural and magnetic properties. The extraordinary sensitivity of the electronic and crystal structures to external parameters such as the application of hydrostatic pressure have led to a systematic investigation over the last years in order to comprehend the microscopic processes taking place in the 5:4 materials. Experimental observations of a Griffiths-like phase (GP) in the paramagnetic (PM) phase at a characteristic temperature TG above the long-range order temperature (either TC or TN) were reported later in these compounds. The appearance of this regime has pointed to arise from the strong interplay between structure and magnetism present in these materials. According to a recent work, this behavior has been found to be restricted to 5:4 compounds which present the monoclinic Gd5Si2Ge2-type (M) or the orthorhombic Sm5Ge4-type (O(II)) of crystal structure at room temperature. The short-range magnetic correlations observed in the M-PM and O(II)-PM phases, an essential ingredient for the existence of Griffiths-like singularities, indicated that the system retains memory of the O(I) phase (pure state) signaled by an anomaly at TG. In this work we report on a detailed study of the pressure effect on the Griffiths-like phase in several compounds of the R5(Si1-xGex)4 ( R = Tb, Gd and Dy) system stable in the M - PM and O (II) – PM phases at room temperature. The selected compounds for this study are representative of O(II)-AFM (R = Gd), O(I)-FM (R = Tb) and O(I)- FM (R = Dy) ground states, respectively presenting GP in both AFM and FM states. For all the analyzed cases, low field - dc susceptibility measurements show that the GP persists at pressures up to 10 kbar. The value of TG, associated with the onset of short-range ferromagnetic correlations, increases linearly with pressure. However, large differences in the rate of change dTG/dP have been observed among them: The rate of the Tb - based compound is an order of magnitude greater than that of the Dy-based compound. Such a different pressure dependence of the Griffiths phase in these compounds could arise from the particular character of the clusters and the competition between the different structural and magnetic phases.
DescripciónResumen del trabajo presentado a la 20th International Conference on Solid Compounds of Transition Elements, celebrada del 11 al 15 de abril de 2016 en Zaragoza (España).
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