Atomic ordering and magnetic properties in Ni2Mn(GaxAl1-x) Heusler alloys

The phase stability and magnetic properties of Ni2Mn(GaxAl1-x) alloys were studied by differential scanning calorimetric and magnetometric measurements, and X-ray diffraction and transmission electronic microscopic observations. The order-disorder transition temperature from the B2 to the L2(1) phase, T-t(B2/L21), linearly increases with increasing x and the magnetic properties depend on the annealing conditions. Especially in the Ni2Mn(Ga0.5Al0.5) alloy, the condition of the atomic order can be varied from a B2 to an L2(1) structure by the annealing temperature. The magnetic property of the fully ordered L2(1) phase is ferromagnetic with a Curie temperature T-C of about 380 K, while that in the B2 phase is antiferromagnetic with the Neel temperature T-N of about 300 K. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.