Modulation On Magnetic And Spin-Dependent Transport Properties Of Facing-Target Reactively Sputtered Fe₄N Films

Antiperovskite-type cubic Fe₄N is a typical ferromagnetic material with a large saturation magnetization,high Curie temperature,high spin polarization,high ductility and corrosion resistance,which has the wide potential applications in spintronics.High storage density,low energy consumption and high speed are the key features of the next generation of spintronic devices.However,the in-plane magnetic anisotropy of Fe₄N limits its practical applications in spintronic devices.Therefore,it is of great value to tailor the structure,magnetic and spin-related transport properties of Fe₄N films by means of doping engineering,strain engineering and interface engineering.In this dissertation,the magnetic and spin-dependent transport properties of facing-target reactively sputtered Fe₄N films are modulated by doping element,bending strain and interfacial effects.The main results of this dissertation are as follows:Polycrystalline Cu Fe₃N films were fabricated on Si（001）and quartz substrates by facing-target reactive sputtering.The magnetic and electronic transport properties of Cu Fe₃N films were investigated.It is found that the saturation magnetization of Cu Fe₃N films is smaller than that of Fe₄N films due to the doping of nonmagnetic element Cu.The magnetoresistance sign of Cu Fe₃N films is opposite to that of Fe₄N films below 20 K due to the competition among the Lorentz force,spin-orbit interaction,weak localization and s-d exchange interaction.Moreover,the transformation from the two-fold to one-fold symmetry appears in the planar Hall resistivity of the 10-nm thick Cu Fe₃N film due to the competition between the temperature-dependent electron scattering and magnetic-field-dependent spin-related scattering.Epitaxial Fe₄N films were fabricated on mica substrates by facing-target reactive sputtering.The saturation magnetization,magnetic anisotropy and electronic transport properties can be effectively tailored by the bending-induced strains.Both the saturation magnetization and squareness of Fe₄N films were enhanced under the bending strains.Moreover,the bending-strain tailored multiresistance states appear.The mechanism of strain-tailored magnetic properties of epitaxial Fe₄N films was analyzed by the first-principles calculations,which provides a theoretical basis for flexible spintronic devices.Epitaxial Ni Mn/Fe₄N bilayers were fabricated on mica substrates by facing-target reactive sputtering.The bending-strain tailored exchange-biased field,coercive field,anisotropy magnetoresistance and planar Hall resistance of Ni Mn/Fe₄N bilayers have been investigated.The variation regulation of bending-strain tailored exchange bias effect appeared,whose mechanism was also analyzed.The efficient modulations on magnetic and electronic transport properties via bending strains provide guidance for the novel spintronic devices.Epitaxial Pt/Fe₄N bilayers were fabricated on Mg O（001）substrates by facing-target reactive sputtering.The effects of Pt layer and Pt/Fe₄N interface on the magnetic and spin-related transport properties have been investigated.The reversals and the nonmonotonic magnetotransport anomaly of Hall curves appear by varying the Fe₄N film thickness,the measuring temperature and external magnetic field.The mechanisms of Pt layer effect on magnetic and electronic transport properties of Pt/Fe₄N bilayers have been analyzed by first-principles calculations and micromagnetic simulations.These results provide the experimental and theoretical basis for the practical applications of Pt/Fe₄N bilayers.