High Frequency Magnetic Properties Of Co₂FeAl Films On Different Substrates

With the rapid development of integration,miniaturization and high-frequency magnetic random memory devices,small size and sensitivity to high-frequency sig-nals are increasingly required.Soft magnetic materials have become the key materials for information processing and storage due to their high magnetic permeability and high resonant frequency.Among them,Co₂FeAl alloy has unique advantages in fields such as high-frequency communication,artificial intelligence,and aerospace due to its high spin polarization rate,high Curie temperature,and low damping factor.However,these properties of Co₂FeAl alloystronglydepend on the degree of crystal structure orderliness and magnetic structure.Therefore,in this paper,Co₂FeAl thin films were sputteredon single crystal Si and single crystal Pb(Mg_1/3Nb_2/3)O₃-Pb Ti O₃（PMN-PT）substrates by magnetron sputtering to explore the effects of substrate type,film thick-ness and applied electric field on crystal structure,transport characteristics and high frequency magnetism of Co₂FeAl thin films.The following conclusions are reached:Theferromagnetic properties of Co₂FeAl thin films with well-ordered structure were investigated.Co₂FeAl thin films were sputtered on single crystal Si substrate by magnetron sputtering.It was found that the crystal structure of Co₂FeAl thin films changed from disordered to ordered with the change of sputtering power,substrate temperature and annealing temperature.Ferromagnetic Resonance was used to test the high frequency magnetic properties of Co₂FeAl films with different thicknesseswhich was found that the magnetic anisotropy and damping in the hard and easy axes in-creased first and then decreased as the thickness of the films increased from 20 nm to200 nm.The reason was that when the film thickness increases,the crystallinity of Co₂FeAl film increased and the interface effect decreased with the increased of grain size,therefor,the magnetic anisotropy increased.When the film thickness exceeded100 nm,the number of magnetic momentwereexcessiveanddeviated from the film sur-face,resulting in the magnetic anisotropy decreases.The transport characteristics and static magnetism of Co₂FeAl/PMN-PT polyfer-ro heterostructure regulated by electric field were investigated.Co₂FeAl films were sputtered on a single crystal PMN-PT ferroelectric substrate.The remanence and co-ercivity showed a volatile sphen-like behavior with the change of electric field,which was consistent with the change trend of the strain curve of PMN-PT substrate.There-fore,the behavior was attributed to the stress effect.The high frequency magnetism of Co₂FeAl/PMN-PT polyferric heterostructure regulated by electric field wasinvestigated.According to the Ferromagnetic Reso-nance test results,it was found that Co₂FeAl film with thickness of 20 nm exhib-iteduniaxial magnetic anisotropy,aswellas the resonance field in the easy axis and the hard axis direction showed a volatile sphen-like behavior with the change of electric field,which was consistent with the results of transport and Magneto-Optical Kerr test,therefor,the behavior was also considered to be caused by stress effects.The test re-sults of Vector Network Analyzer showed that the internal uniaxial magnetic anisotro-py decreased and the damping decreased under the residual polarization state.