Magnetism Modulation Of Co₂FeAl Huesler Alloys

With development of spintronics,it has been found that high spin polarization and low damping factor can increase the reversal ability of magnetization.Co₂FeAl Heusler alloys show great potential applications because of the high spin polarization,low damping factor and high Curie temperature.However,the above properties of the Co₂FeAl alloys strongly depend on the order of atomic distribution in the crystal lattice,the morphology of the grain and the magnetic structure.Therefore,the magnetic properties of the Co₂FeAl alloys are modulated by adjusting film thickness,substrate temperature and applied electric field.The main results obtained are shown as follows.（1）Thickness dependence of magnetic anisotropy and damping factor was found in the Co₂FeAl/Si films.When the thickness of the Co₂FeAl films increase from 20nm to 120 nm,the in-plane uniaxial anisotropy field changes from 120 Oe to 90 Oe,and the resonance frequency drops from 3 GHz to 2 GHz.At the same time,by fitting the FMR spectra,it is found that the extrinsic line width(H_ex)increases with the increase of the films thickness,and the intrinsic line width(H_in)is independent of the films thickness.Therefore,the intrinsic damping factor of the films does not change.（2）The modulation of the semi-metallic abundance and damping factor of Co₂FeAl/PMN-PT is achieved by changing the temperature of the substrate.By comparing the peak intensity of the（002）and（004）diffraction in XRD spectra the Huesler alloys change from a highly ordered B2 phase to an A2 phase as the substrate temperature decreases from 500°C to 350°C.At the same time,the corresponding AMR changes from negative to positive,and the alloys loss their semi-metallic properties.As the substrate temperature decreases,the resonance field and line width increase,the saturation magnetization decreases,and the intrinsic damping factor increases significantly.（3）The modulation of static magnetic properties by electric field is realized in the Co₂FeAl/PMN-PT heterojunction.By measuring the remanence along the[100]and[01-1]directions,a non-volatile remanent change was found under electric field.This is mainly due to the change of the effective anisotropy caused by the stress anisotropy induced by the substrate.Two reversible stable remanent states can be obtained by applying a pulsed electric field along the[100]and[01-1]directions of the heterojunction respectively.This remanent polymorphism can be used for polymorphic storage.（4）The dynamic magnetic modulation of the semi-metal Heusler alloys Co₂FeAl/PMN-PT heterojunction is realized under electric field.Applying a longitudinal DC electric field in the heterojunction,the resonance field and line width of the FMR spectra exhibit a non-volatile loop-like curve.This can be attributed by the changes of the effective anisotropy magnitude and direction,which results from a109°reversal of the ferroelectric domain in the PMN-PT substrate.