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

Experimental studies of the physical properties of the three equiatomic com pounds GdMgX (X = Al, Ga, In) are reported. GdMgAl (MgCu2-type structure) o rders ferromagnetically below 59 K. Between 70 and 300 K it follows the Cur ie-Weiss law with mu (eff) = 8.59 mu (B) and theta (p) = +70 K. The magneti sation, in the ordered state, saturates almost completely at 5 K in a magne tic field of 9 Tesla (mu (sat) = 6.71 mu (B)). From several magnetisation i sotherms 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. T he crystal structure of the two new phases GdMgGa and GdMgIn (hexagonal ZrN iAl-type structure) is determined by single crystal X-ray analysis and the positional and displacement parameters refinements of both compounds are re ported. GdMgGa orders antiferromagnetically at 15.3 K; above 50 K the compo und follows the Curie-Weiss law with theta (p) = 124.5 K and mu (eff) = 7.5 2 mu (B). 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, theta (p) = -130.5 K and mu (eff) = 7.75 mu (B) are obtained. The magnetisa tion of the two compounds does not saturate at 5 K in an applied magnetic f ield of 9 T (mu (sat)(GdMgGa) = 0.88 mu (B), mu (sat) (GdMgIn) = 1.05 mu (B )). (C) 2000 Elsevier Science B.V. All rights reserved.