Controllable synthesis of γ′-Fe_4N via prolonged high vacuum magnetic annealing of deposited Fe-N thin films

摘要

In order to develop a fast and low-cost method for preparing gamma'-Fe4N thin films for spintronic applications, the iron nitride (Fe-N) thin films were deposited through reactive sputtering in pure nitrogen, followed by high vacuum magnetic annealing process. The X-ray diffraction pattern (XRD) results revealed that the N content of the Fe-N thin films were decreasing continuously with the increase of annealing temperatures and times, so as to affect their crystal phase compositions, thus a single phase of gamma ''-FeN, xi-Fe2N and gamma'-Fe4N can be controllable prepared through annealing process. The phase transition characteristics for Fe-N to gamma'-Fe4N were studied carefully. It was found that the sample (Fe1.8N) with a mixed crystal phase of gamma ''-FeN and xi-Fe2N can be totally changed into a single phase of gamma'-Fe4N by annealing it at 430 degrees C for 3 h, and the annealing temperatures can also be as low as 375 degrees C but for a prolonged time to 24 h. The stoichiometric matter of the as-prepared Fe-N thin films was confirmed by the XPS analysis. The vibrating sample magnetometer (VSM) results indicated that the magnetic properties of the Fe-N thin films are mainly depending on their crystal phase compositions. The saturation magnetization (M-s) of y'-Fe4N films depends on various factors, and it was to about 1080 emu/cm(3) for the gamma'-Fe4N/MgO/Si.