Preparation Of Spin-Pinned Magnetic Nano-Film And Its Application On Microstrip Filter

Radio and microwave frequency magnetic devices based on magnetic materials are essential basic components in today's military and civilian communication systems,such as magnetic tunable filters,circulators and phase shifters.As communication equipment generally develops in the direction of miniaturization,integration and high frequency,this also requires the development of magnetic devices in the direction of miniaturization,integration and high frequency.The saturation magnetization of the permalloy(Ni₈₁Fe₁₉)is 10 k Gs,and its working frequency can reach 9.7 GHz under 1k Gs external magnetic field.Therefore,metal soft magnetic film materials with high saturation magnetization and high magnetic permeability have great prospects in the application of radio and microwave frequency.The research in this dissertation is based on NiFe multilayer films.In terms of materials,it mainly focuses on the microstructure,static magnetic properties,and dynamic properties of the NiFe film which pinned by antiferromagnetic material?FeMn?,low saturation magnetization material?Ni?,and high saturation magnetization material?Fe?.In terms of devices,research work is carried out on the principle and design implementation of magnetic tunable band-stop filters based on the magnetic multilayer films.Firstly,NiFe/FeMn/NiFe multilayer films were prepared on Si?111?substrates by DC magnetron sputtering,and the FeMn film is the intermediate layer.The effects of NiFe film thickness and FeMn film thickness on the microstructure,static magnetic properties and dynamic magnetic properties of the multilayer films were successively studied.The research results show that:As the thickness of the NiFe film increased,the multilayer film changed from vertical growth to lateral growth,the critical thickness was 50 nm,and the minimum surface roughness?R_a=2.3 nm?and minimum average grain size?D=94 nm?were obtained at 50 nm NiFe film;The relationship between coercivity,surface roughness and average grain size was clarified.The studies showed that the magnetostatic energy in samples with large roughness and small grain size is much larger than that in samples with small roughness and large grain size,thereby enhanced the coercivity.The ferromagnetic resonance field showed a downward trend with the increasing thickness of NiFe film,and the ferromagnetic resonance linewidth first decreased and then increased.The optimal performance of the film is obtained when the NiFe film is 50 nm:4?M_s=9073 Gs,H_c=0.61 Oe,?H=95 Oe,H_r=970 Oe.Secondly,in the aspect of double-sided pinning of NiFe film,the effects of NiFe film thickness and FeMn film thickness on the microstructure,static magnetic properties and microwave loss of FeMn/NiFe/FeMn multilayer films are successively studied.The results manifest that:The performance of the multilayer film induced by the FeMn film as a buffer layer is inferior to the multilayer film induced by the NiFe film,which has larger surface roughness and poor static magnetic properties;As the thickness of the NiFe film increases,the growth mode of the film transitions from vertical growth to lateral growth.The grain size increases first and then decreases,reaching a minimum value of 32 nm at 50 nm NiFe film thickness.As the thickness of FeMn increases,the grains of the multilayer film are in the vertical growth mode,and the average grain size and surface roughness are on a downward trend.As the thickness of the antiferromagnetic layer increases,the saturation magnetization shows increasing trend.The coercivity presents a trend of first decreasing and then increasing.The optimal performance of the film is obtained when the FeMn film is 15 nm:4?M_s=9048Gs,H_c=3.017,H_r=1023 Oe.Thirdly,based on the Ni film with low saturation magnetization,the effect of the change of Ni film thickness on the microstructure,static magnetic properties,ferromagnetic resonance linewidth and exchange stiffness coefficient of Ni/NiFe/Ni multilayer film are studied.The results show that:As the thickness of the Ni film increases,the growth mode of multilayer film changes from vertical growth to lateral growth,with a critical thickness of 8 nm.And the multilayer films obtain a lower surface roughness?R_a=5.85 nm?and minimum average grain size?D=82 nm?at 8 nm Ni film.Ni film with low saturation magnetization has a strong pinning effect on NiFe film,and can effectively excite perpendicular standing spin wave.When the thickness of the Ni film increases from 2 to 8 nm,the perpendicular standing spin-wave field?H_P?increases from 683 to 967 Oe at 9 GHz.The perpendicular standing spin-wave disappears when the Ni film thickness reaches 10 nm,indicating that the large grain size will cause the pinning effect to be weakened.As the thickness of the Ni film increases,the exchange stiffness coefficient?A?first decreases and from 15.08×10^-12 to 8.52×10^-12J/m,and then increases to 9.46×10^-12J/m at 8 nm Ni film thickness.The results show that by adjusting the thickness of the pinned layer?Ni film?,the saturation magnetization,gyromagnetic ratio and exchange stiffness coefficient of the film can be effectively adjusted.Then,based on the Fe film with high saturation magnetization,the influence of Fe film thickness change on the microstructure,static magnetic properties,ferromagnetic resonance linewidth and exchange stiffness coefficient of Fe/NiFe/Fe multilayer films are studied.The results show that:Fe/NiFe/Fe film induced by Fe film has an extremely flat and dense morphology,and its surface roughness and average grain size decreased first and then increased with the increasing Fe thickness.With the increase of Fe film thickness,the saturation magnetization and ferromagnetic resonance linewidth both increased.It has a better overall performance at 8 nm:4?M_s=12604 Gs,H_c//=8.99 Oe,?H=84.24 Oe;Fe films with high saturation magnetization have a strong pinning effect on NiFe films,which can effectively excite perpendicular standing spin wave.When the thickness of the Fe film increases from 4 nm to 15 nm,the vertical spin wave field?H_P?increases from 133 to 379 Oe,and the perpendicular standing spin-wave linewidth??H_p?increases from 68 to 148 Oe;With the increase of Fe film thickness,the ferromagnetic resonance linewidth of the multilayer film increased from 111.5 to 140.3 Oe,and the exchange stiffness coefficient decreased from 22.1×10^-12 to 7.8×10^-12J/m.Finally,based on the Fe/NiFe/Fe multilayer film with the best performance,a series of microwave band stop filters are prepared,tested and analyzed at room temperature.The results show that:Compared with NiFe single-layer film microstrip band stop filter,the center frequency of the spin-pinned Fe/NiFe/Fe multilayer film microstrip band stop filter is increased by 1.9 GHz.For Fe/NiFe/Fe multilayer thin film microstrip band stop filters,as the linewidth increased,the center frequency moves to high field,but the in-band attenuation is smaller.Compared to the linear structure,the curved structure has a larger in-band attenuation.