Spontaneous Magnetization and Magnon-TA Phonon Interaction during the Premartensitic Transformation in Ni₂ MnGa Alloy

The magnetic anomaly associated with the premartensitic transformation (PT) in Heusler alloy Ni₂MnGa is investigated by using the Green's function technique based on the magnon-TA phonon interaction. The results of the numerical calculations suggest that the magnetic anomaly during the PT may originate from the strong magnon-TA phonon interaction, because this kind of coupling effect will destroy the magnetic ordering in some local zones and reduce the magnetization of the system. Magnon-magnon interaction plays a positive role in enhancing the magnetization and tends to reduce the PT temperature while this kind of interaction has little effect on the characteristic TA phonon-wavevector corresponding to the anomaly of spontaneous magnetization at the PT temperature.