Growth Of Iron Nitride Films By Pulsed Laser Deposition

Iron nitride is an important iron alloy with superior corrosion resistance, mechanical hardness and magnetic properties, which makes it very attractive for a number of applications including protective coating of steels, magnetic fluids, magnetic recording and catalysis, etc. The nitrogen poor phasesα"-Fe16N2 andγ'-Fe4N have stimulated the most intense research interest because of their excellent magnetic properties together with corrosion resistance. The giant saturation magnetization was observed in Fe-N films and a"-Fe16N2 phase, which is higher than any soft magnetic materials in existence. In terms ofy'-Fe4N, this is a simple structure Fe-N phase, and possessed some attractive magnetic properties, such as high spin-polarized transport, which makes it interesting to apply in magnetic thin film devices, e.g. magnetic tunnel junctions (MTJs).In order to fabricate special structure Fe-N films, various methods have been applied, e.g. reactive sputtering, ion beam assisted deposition, molecular-beam epitaxy, mechanical alloying, chemical vapor deposition and ion implantation, etc. However only few groups have previously reported results of Fe-N films deposited by the technology of reactive pulsed laser deposition (PLD). PLD is a facile method to grow special structure metallic films at nonequilibrium conditions. In the present work, Fe-N thin films have been deposited by reactive PLD at various nitrogen pressures.In series of Fe-N films, a anomalous Ms increase was observed for the films deposited at 8 mTorr nitrogen pressure. In addition, it was surprised to find that the a-Fe phase of Fe-N films deposited at 8 mTorr exhibited the same lattice constant of 2.8705A. According to the analysis of XRD and CEMS, this anomalous Ms increase in Fe-N films was speculated to due to a heterogeneous state ofγ'-Fe4N and Fe mixture. The calculated nitrogen concentration of the Fe-N film deposited at 8 mTorr is approximately 9.1%, which is very close to the value of 11.1% forα"-Fe16N2 phase. Considering the magnetic properties and nitrogen concentration, it can be concluded that the optimal nitrogen pressure for obtaining giant Ms Fe-N films is near 8 mTorr.XRD results confirmed that the 10 mTorr is the optimal nitrogen pressure for obtaining single phaseγ'-Fe4N films. Furthermore, it is the first time that the (001)-orientedγ'-Fe4N film was successfully deposited on Si (100) substrate at relatively low deposition temperature of 150℃by pulsed laser deposition technique. The (001) preferred orientationγ'-Fe4N film exhibited in-plane magnetic isotropy and out-plane magnetic anisotropy. This out-plane magnetic anisotropy is speculated to due to the magnetic anisotropy in film interface. The out-plane magnetic anisotropy soft magnetic films applied in special magnetic thin film devices can greatly improve the performance properties of film devices, reduce the devices size.