NiAl Thin Films Research Articles

Kinetics of ion-induced transformations inβ-NiAl thin films as characterized byin situelectrical resistivity measurements

In situ electrical resistivity of thin film $\ensuremath{\beta}$-NiAl at 77 K under 120 keV ${\mathrm{Ar}}^{+}$ irradiation has been measured as a function of the total dose for film thickness of 25, 37.5, 50, 62.5, and 75 nm. A qualitative change was observed in the resistivity versus dose behavior for 50 nm films that cannot be explained by the standard kinetic models. It is shown that depth-dependent cross sections account for the phenomenon as well as for the variety of dose-dependent electrical behaviors reported in the literature.

Effects of Sputtering Conditions on Texture, Microstructure and Magnetic Properties of the CoCrPt/NiAl Thin Films

AbstractThe effects of sputtering argon pressures and sputtering power on the microstructure, texture and magnetic properties of NiAI underlayers on CoCrPt films were investigated. In this paper, the relationship between the sputtering conditions, microstructure, crystallographic texture and magnetic properties of these thin films will be discussed. By controlling the sputtering pressure and sputtering power, the texture and microstructure of NiAI underlayers were found to vary. This in turn was found to influence the magnetic properties of CoCrPt thin films. It was found that 10 mtorr is the optimum pressure to deposit the NiAl thin films to obtain the best magnetic properties for our system. At this argon pressure, the coercivity reached a maximum value because of the strongest CoCrPt (1010) texture and smallest grain size. At lower argon pressures (< 10 mtorr), NiAI tended to have a (110) texture reducing the CoCrPt (1010) texture, which in turn reduced the CoCrPt coercivity and S*. Also, high NiAl deposition pressures (>30 mtorr) yielded larger grains and a weaker CoCrPt (1010) texture, thereby decreasing the coercivity of the CoCrPt films. Increasing the sputtering power has been found to increase the CoCrPt coercivity and S* value. However, the grain sizes of the CoCrPt/NiAl thin films deposited at higher sputtering power were larger than those obtained at lower sputtering power.

The extraordinary Hall effect in coherent epitaxial τ (Mn,Ni)Al thin films on GaAs

Ultrathin coherent epitaxial films of ferromagnetic τ(Mn,Ni)0.60Al0.40 have been grown by molecular beam epitaxy on GaAs substrates. X-ray scattering and cross-sectional transmission electron microscopy measurements confirm that the c axis of the tetragonal τ unit cell is aligned normal to the (001) GaAs substrate. Measurements of the extraordinary Hall effect (EHE) show that the films are perpendicularly magnetized, exhibiting EHE resistivities saturating in the range of 3.3–7.1 μΩ-cm at room temperature. These values of EHE resistivity correspond to signals as large as +7 and −7 mV for the two magnetic states of the film with a measurement current of 1 mA. Switching between the two magnetic states is found to occur at distinct field values that depend on the previously applied maximum field. These observations suggest that the films are magnetically uniform. As such, τ(Mn,Ni)Al films may be an excellent medium for high-density storage of binary information.

MBE growth of ferromagnetic (Mn,Ni)Al thin films on AlAs/GaAs

We describe the coherent epitaxy of MnNiAl fenomagnetic thin films on AlAs/GaAs heterostructures using molecular beam epitaxy. The epitaxy helps to stabilize the τ phase, which is known to be a metastable ferromagnetic phase with a tetragonal lattice. The easy axis of the ferromagnetic thin film is oriented perpendicular to the surface as a consequence of the coherent epitaxy. The results of structural and magnetic analysis are given for thin Mn x Al 1- x films with 0.40 < x < 0.60. We have further assessed the change in structural and magnetic properties of the thin films when Ni is added as a substitution for Mn in Mn 0.60- y Ni y Al 0.40, with 0 < y < 0.18. We find that coherent epitaxy is obtained over these wide compositional ranges and that the change in magnetic properties using various Ni additions adds a degree of freedom in the design of ferromagnetic thin layers on AlAs/GaAs for future device structures.

Fabrication of Ni–Al thin films by the pulsed laser deposition technique

We have fabricated Ni3Al and NiAl thin films on different substrates by the pulsed laser deposition (PLD) technique. A high energy nanosecond laser beam was directed onto Ni–Al (NiAl, Ni3Al) targets, and the evaporated material was deposited onto substrates placed parallel to the target. The substrate temperature was varied between 300 and 400 °C, and the substrate-target distance was maintained at approximately 5 cm. The films were analyzed using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry. At energy densities slightly above the evaporation threshold, a slight enrichment of Al was observed, while at higher energy densities the film stoichiometry was close (&lt;5%) to the target composition. Barring a few particles, the surface of the films exhibited a smooth morphology. X-ray and TEM results corroborated the formation of Ni3Al and NiAl films from similar target compositions. These films were characterized by small randomly oriented grains with grain size varying between 200 and 400 Å.

High-temperature growth of epitaxial NiAl thin films on AlAs by molecular-beam epitaxy

Good NiAl single-crystal films were successfully grown on AlAs at high temperature (600 °C) by means of molecular-beam epitaxy. It was found that there existed three characteristic temperature regions in the crystal growth. Below 300 °C, the in situ formation of NiAl failed. Above 300 °C, NiAl was formed in situ, while other Ni-Al intermetallic compounds (Ni3Al2, NiAl3, Ni3Al) also appeared. Above 400 °C, remarkable improvements of the crystallinity, epitaxy, and monocrystallinity were found. The best NiAl film was obtained at 600 °C, where no interfacial disorder attributed to the interdiffusion and no film discontinuity due to balling up were observed. It is suggested that high-temperature growth is powerful for synthesis of high-quality NiAl-(Al,Ga)As heterostructures.

Ion-induced phase formation in Ni-Al and Fe-Al thin films: Role of chemical disordering energy on amorphization

Phase formation in the metallic systems Ni/Al and Fe/Al by ion beam mixing is studied at low temperature when chemical diffusion is prevented. Chemical disorder or/and topological disorder are therefore observed. Thermodynamic analysis based on free energy diagrams shows that stored energy in antisite defects in intermetallic compounds plays a determining role. Chemical disorder, by raising the energy of the crystal lattice, induces the transformation towards the amorphous state. The dissimilar results obtained for equiatomic ordered compounds FeAl and NiAl can be easily understood in this regard. Moreover a high mixing energy in the twc phases regions can explain the preferential stability of the topological disordered state.