Quantitative correlation of phase structure with the magnetic moment in rf sputtered Fe-N films

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Abstract
Single-layer Fe-N films were deposited onto DC biased glass substrates at room temperature by reactive rf magnetron sputtering in an N2-Ar atmosphere. The Ar pressure was fixed at 6 mTorr and the properties were investigated as a function of N2 flow rate (R). X-ray diffraction and transmission electron diffraction were used to identify phases in the films. At R=0, the saturation magnetic moment density σS measured in a vibrating-sample magnetometer (VSM) was 210 emu/g, within experimental error equal to the value for bulk α-Fe, and only a single phase with the bulk lattice constant of α-Fe was detected. At R=5 sccm, σS=227 emu/g, and an α-Fe(N) phase with a ∼1% expanded lattice constant was detected. At R=15 sccm, σS reached a maximum of 247 emu/g and x-ray and transmission electron diffraction gave clear evidence of the Fe16N2 phase in addition to α-Fe(N). At R=30 sccm, σS dropped to 196 emu/g, and the diffraction data showed α-Fe, α-Fe(N), and a significant fraction of Fe4N. The value of σS calculated from the volume fractions of each phase estimated from transmission electron microscopy statistical sampling of single grain diffraction quantitatively agreed, within the experimental error, with the measured value.