Low Temperature Deposition of Ferromagnetic Ni-Mn-Ga Thin Films From Two Different Targets via rf Magnetron Sputtering
- PDF / 225,131 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 65 Downloads / 154 Views
1250-G08-02
Low Temperature Deposition of Ferromagnetic Ni-Mn-Ga Thin Films From Two Different Targets via rf Magnetron Sputtering
A. C. Lourenço1, F. Figueiras1, S. Das1, J. S. Amaral1,5, G. N. Kakazei5, D. V. Karpinsky1, N. Soares1, M. Peres2, M. J. Pereira1, N. M. Santos2, P. B. Tavares4, N. A. Sobolev2, V. S. Amaral1 and A. L. Kholkin3 1
Department of Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal
2
Department of Physics, I3N, University of Aveiro, 3810-193 Aveiro, Portugal
3
Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal
4
Centro de Quimica, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal 5
IFIMUP-IN and Departamento de Física e Astronomia da Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal
ABSTRACT Low temperature (400°C) deposition of ferromagnetic Ni-Mn-Ga thin films is successfully performed via rf magnetron sputtering technique using co-deposition of two targets Ni50Mn50 and Ni50Ga50 on sapphire (0001) and Si (100) substrates. The films are in part amorphous with significant degree of crystallinity. The obtained crystallographic structure is shown to be substrate-dependent. Films on both substrates are ferromagnetic at room temperature (Curie temperature ~ 332 K) demonstrating well-defined hysteresis loops, low coercivity (~ 100 Oe), and saturation magnetization of ~ 200 emu/cc. At low temperature (5 K), both films are characterized by increased magnetization and wider hysteresis loops with higher coercivity and remanent magnetization. The process is therefore effective in achieving the appropriate thermodynamic conditions to deposit thin films of the Ni-Mn-Ga austenitic phase (highly magnetic at room temperature) at relatively low substrate temperature without the need for post-deposition annealing or further thermal treatment, which is prerequisite for the device fabrication.
INTRODUCTION Ni–Mn–Ga thin films hold great promise in obtaining a shape memory effect with a high power density and a low driving field. The films can be produced by different techniques like sputtering [1], pulsed laser deposition [2-3], molecular beam epitaxy [4], or flash evaporation [5]. However, a magnetically induced reorientation of the martensite variants is observed only in few cases. Recent work by Heczko et al. [6] showed a distinct
room temperature shape memory effect in a substrate-constrained film, which was attributed to the magnetic field induced reorientation of a small percentage of the twin variants. These results provide us the evidence and requirement for developing the growth/preparation conditions to optimize the shape memory effect by improving the crystallinity and microstructure of these films. Ni–Mn–Ga films having room temperature ferromagnetism needs sufficiently high deposition temperatures [2], which, on the other hand, disrupts the corresponding stoichiometric compositions. General approach is therefore taken by depositing the films at low t
Data Loading...
