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 L21 phase, TtB2/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 L21 structure by the annealing temperature. The magnetic property of the fully ordered L21 phase is ferromagnetic with a Curie temperature TC of about 380 K, while that in the B2 phase is antiferromagnetic with the Néel temperature TN of about 300 K.