Effect Of Cobalt Addition On Structure And Properties Of FeN Thin Films

Iron nitrides（Fe–N）are an important class of material in basic research and practical application.Especially α’’-Fe₁₆N₂ phase has a large saturation magnetization values and magnetic anisotropy what provid the conditions of a large magnetic energy product.It has important application in high density magnetic recording aspect and has good potential for use in rare-earth-free permanent magnets,magnetic writers,and spintronic devices in the future.Fe,FeN,and a series of FeCoN thin films were deposited on glass substrates at RT by DC magnetron sputtering and subsequently annealed.The structures were determined by X-ray diffraction（XRD）and TEM.The morphological analyses of the samples were conducted by scanning electron microscopy（SEM）and Atomic force microscopy（AFM）.Magnetic force microscopy（MFM）measurements were performed to determine the domain structures on the surface of the ?lms.The magnetic properties and △ M curve were measured by a vibratingsample magnetometer（VSM）.In this study,we describe the surface morphology,structure,magnetic properties and resistivity of N and Co additions in pure Fe film and study the properties of a series of Co-containing different concentration of FeCoN films.We choose the optimum Fe CoN film and study its thermal stability.Intergranular interactions were studied by means of Delta-M curve.The results are summarized as follows:（1）As N was introduced,α’’ phase appears in the Fe film and proper Co addition helps to enhance the α’’ phase.The magnetization and resistivity in FeN film improved with the addition of Co,and the value of Ms in the sample FeCoN was about 2088 emu/cm3,and the resistivity of our FeCoN ?lm was 455.5 μΩ cm.Moreover,the FeCoN film has a large perpendicular anisotropy,which is the reason to produce a clear striped domain structure in sample.（2）The α’’ phase enhanced and Ms reached a maximum value of2088 emu/cm3 as the Co concentration reached to a value of 13.2 at%by comparing the structure and properties of a series of Co-containing different concentration of FeCoN film.At this time,the resistivity of FeCoN ?lm is higher.Therefore,Co concentration reached to a value of 13.2 at% helps to enhance the α’’ phase and improves a variety of properties.（3）At 13.2 at% of Co,the FeCoN films annealed at differenttemperatures for the same period of time.The FeCoN film annealed at200℃ show very high saturation magnetization and the α’’ phase is stable up to 450℃.While FeN and FeCoN film were exposed to the air for some time at room temperature,the improvement of thermal stability of α’’ phase in FeCoN thin film was also found.We report on the analysis of the intergranular（IG）interactions in the Fe,FeN and FeCoN films.Intergranular interactions were studied by means of Delta-M curve and the positive Delta-M means that exchange dominates the IG interactions in three films.This finding is in good agreement with grain size data.Because magnetic domain is larger than grain size.In summary,proper Co addition can not only help to enhance theα’’ phase and improve Ms,can also has an increase in resistivity.These properties indicated that the FeCo N film had good potential for use in rare-earth-free permanent magnets and became a new magnetic material.