Crystallographic, magnetic and magnetocaloric properties of GdMgX intermetallic phases (X=Al, Ga, In)

Experimental studies of the physical properties of the three equiatomic compounds GdMgX (X=Al, Ga, In) are reported. GdMgAl (MgCu2-type structure) orders ferromagnetically below 59 K. Between 70 and 300 K it follows the Curie-Weiss law with μeff=8.59 μB and θP=+70 K. The magnetisation, in the ordered state, saturates almost completely at 5 K in a magnetic field of 9 Tesla (μsat=6.71 μB). From several magnetisation isotherms between 10 and 120 K, the total entropy change and the refrigerant capacity of the material at 1.5, 3 and 5 T magnetic fields is evaluated. The crystal structure of the two new phases GdMgGa and GdMgIn (hexagonal ZrNiAl-type structure) is determined by single crystal X-ray analysis and the positional and displacement parameters refinements of both compounds are reported. GdMgGa orders antiferromagnetically at 15.3 K; above 50 K the compound follows the Curie-Weiss law with θP=-124.5 K and μeff=7.52 μB. On the contrary, no evidence of a magnetic order is observed for the GdMgIn phase. From the Curie-Weiss law, applied in the 70-290 K range, θP=-130.5 K and μeff=7.75 μB are obtained. The magnetisation of the two compounds does not saturate at 5 K in an applied magnetic field of 9 T (μsat(GdMgGa)=0.88 μB, μsat(GdMgIn)=1.05 μB). (orig.)