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

The Gd₅Si_2.75P_1.25 phase with all interslab Si/P–Si/P dimers broken (Sm₅Ge₄-type structure) undergoes a ferromagnetic transition at 184 K. For this phase, the magnetocaloric effect in terms of the magnetic entropy change, ΔS, reaches the maximum value of −7.8 J/kg K at 177 K. 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. Gd₅Si_3.5P_0.5 and Gd₅Si_3.25P_0.75, 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 336 K to 332 K in Gd₅Si_3.25P_0.75.