Magnetic and structural properties of nonstoichiometric Ni2MnGa alloys with Ni and Ga excess

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Abstract
The influence of nickel and gallium excess on local structure and magnetic properties of Ni–Mn–Ga alloys has been studied. Nuclear magnetic resonance experiments showed that excessive Ni occupies Mn and Ga positions. This leads to the appearance of low-frequency line from the nearest Mn55 nuclei and generation of fractional nuclear echo signals due to the increase of electrical field gradients on these nuclei. Magnetic measurements revealed the difference of Curie temperature determined from ac susceptibility and extrapolated from high-temperature magnetization behavior. The most probable explanation of this fact is the reduction of manganese–manganese indirect exchange via the faults in Mn–Ga layers interchange caused by excessive Ga.