Martensitic transformation in Ni2MnGa magnetic shape memory alloy thin films

Abstract

This project focuses on Ni2MnGa thin film and its aim is to obtain the five-modulated (5M) martensite. Direct Current (DC) Sputtering was applied to prepare Ni-Mn-Ga thin films on SiNx/SiO2/Si and PLZST/Pt/Ti/SiO2/Si substrates. The samples were deposited in Ar atmosphere at different sputtering power based on different type of heat treatments used; vacuum annealing and rapid thermal process. In particular, the crystal structure and magnetic properties of the thin films were investigated as a function of sputtering and heat treatment parameters by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX) and Alternating Gradient Magnetometer (AGM). The results show that different types of heat treatments, sputtering and heat treatment parameters significantly influence the structure and magnetic properties of the thin films. When vacuum annealing was used, the films were prone to diffusion and oxidation problems. Consequently, the 5M structure was not obtained and the saturation magnetization obtained was small. For rapid thermal process, Ni-Mn-Ga thin films were found magnetic at annealing temperature of 600oC even though oxide phases still remained in the films. Fast Fourier Transform (FFT) revealed the possibility of the presence of 5M structure. It was found that higher annealing temperature and dwelling duration promote the formation of oxide phases. For sputtering power, we observed that the higher the sputtering power, the lower the magnetic properties of the films.