Doping effect on the martensitic and magnetic phase transitions of Heusler-type Ni2MnGa

Summary form only given. While Heusler-type Ni₂MnGa exhibits both ferromagnetic and martensitic phase transitions at 380 K and 220 K, respectively, Ni₂MnAl with the L2₁ structure shows only a ferromagnetic ordering near room temperatures. In this work, we alloyed both compounds with different Al/Ga ratio to study the interplay between martensitic and magnetic phase transitions of Ni₂MnGa_1-xAl_x. Results indicate that both martensitic and magnetic transition temperatures considerably increase for the low Al concentration (x <; 0.04). However, upon substituting more Al (x > 0.10), a drastic suppression of martensitic transition along with a linear decrease of magnetic ordering temperature takes place. Such observations are in contrast to the general expectation for the nonmagnetic doping. It thus points out that the effect of disorder introduced by the Al substitution should play an important role on the phase transition characteristics of these alloys.