Magnetic transitions in the Gd5Si4−xPx (x=0.5, 0.75, 1.25) phases. Magnetocaloric effect of the Gd5Si2.75P1.25 phase

The Gd5Si2.75P1.25 phase with all interslab Si/P–Si/P dimers broken (Sm5Ge4-type structure) undergoes a ferromagnetic transition at 184K. For this phase, the magnetocaloric effect in terms of the magnetic entropy change, ΔS, reaches the maximum value of −7.8J/kgK at 177K. Absence of a temperature-dependant structural transition, as confirmed by the low-temperature single crystal diffraction studies, together with the moderate value of ΔS points to the presence of a conventional magnetocaloric effect. Gd5Si3.5P0.5 and Gd5Si3.25P0.75, which are composites of the Gd5Si4- (all Si/P–Si/P dimers intact) and Sm5Ge4-type phases, possess two magnetic transitions associated with the two-phases. Introduction of P into Gd5Si4 lowers the Curie temperature from 336K to 332K in Gd5Si3.25P0.75.