Magnetic and magnetocaloric properties of the coloured Heusler phases GdAg2Mg and REAgAuMg (RE=Gd, Tb, Dy)

Abstract

Abstract The magnetocaloric effect (MCE) of the ferromagnetic compound GdAg2Mg [T C=98.3(5) K] was investigated along with its electrical resistivity and the specific heat capacity. The magnetic entropy changes (–ΔS M) as well as the changes in adiabatic temperature (ΔT ad) have been calculated from these data. Furthermore, the magnetic susceptibility of the pseudo-quaternary Heusler phases GdAgAuMg, TbAgAuMg and DyAgAuMg [i.e. RE(Ag0.5Au0.5)2Mg] were measured and compared to the data for the pure silver and gold compounds REAg2Mg and REAu2Mg. The substitution of the transition metal at the crystallographic Wyckoff site 8c influences the magnetic ground state of the trivalent rare earth metals and therefore drastically alters the Curie temperatures. The structure of GdAgAuMg was refined from single crystal X-ray diffraction data, revealing a small deviation from the equiatomic composition leading to the refined formula GdAg0.92(6)Au1.08(6)Mg [space group Fm3̅m, Z=4, a=695.03(10) pm, wR2=0.0883, 55 F 2 values, six parameters]. The intermetallic compounds were synthesised in sealed niobium ampoules under high temperature conditions. They have reddish to brassy colour.