| With the rapid development of communication,high density magnetic recording and radar technology,the requirement for high frequency and integration of devices is becoming higher and higher,and high performance soft magnetic materials with working frequency in GHz band are urgently needed.In many important technical fields such as electromagnetic signal conversion,magnetic information writing,electromagnetic shielding,microwave integrated circuits,soft magnetic materials are required to have the highest high-frequency permeability in the GHz frequency range.However,according to Acher limit,the natural resonance frequency and permeability of traditional single-layer ferromagnetic are limited,while the magnetic sandwich structure with antiferromagnetic coupling possesses higher resonance frequency and permeability.The sandwich structure of ferromagnet/nonmagnet/ferromagnet(FM/NM/FM)with interlayer coupling and uniaxially anisotropic system was grown on a single crystal Si substrate by the co-induction of external magnetic field and oblique sputtering.The interlayer exchange coupling and high-frequency magnetism were studied by the means of vibration sample magnetometer(VSM)?vector network analyzer(VNA)and temperature-dependent ferromagnetic resonance(CryoFMR).New materials,principles and methods were provided to break through Acher limit and improve the working frequency of magnetic devices.Our main research contents are as follows:(1)The sandwich films of FM/NM/FM were prepared by magnetron sputtering.With the increasing the NM layer,the VSM datas showed that the coupling mode between the two layers changed from ferromagnetic to antiferromagnetic coupling,and the coupling strength decreased.Ferromagnetic resonance was used to characterize the dynamical magnetic properties of the antiferromagnetic coupled sample,two ferromagnetic resonance modes of acoustic and optical,which are characterized by inphase and out-of-phase precession of the moments,were observed.The experimental results are consistent with the theoretical RKKY interaction,therefore,we can realize the ferromagnetic or antiferromagnetic coupling by changing the thickness of the nonmagnetic layer.(2)The sample of FeNi(20 nm)/Ru(1.0 nm)/FeNi(20 nm)/Si with strong interlayer antiferromagnetic coupling was selected by VSM.,The absorption spectra of the acoustic mode and optic mode at different temperatures were obtained via frequencydependent ferromagnetic resonance measurements.By fitting the absorption spectra of the two modes using the Kittel equation,we found that the exchange coupling field,which is related to the interface and the spin-wave excitations,decreases with increasing temperature.The experimental results shown that the optical mode damping is significantly higher than that of the acoustic mode.The Gilbert damping including an additional nonlocal damping due to the pump spin effect in the interface does exist in the out-of phase precess mode and it is related to the strength of the interlayer coupling.(3)In this part,the dependence of complex permeability on frequency of FM/NM/FM sandwich structure with interlayer antiferromagnetic coupling was obtained by vector network analyzer.The optical resonance with higher natural resonance frequency and permeability can be controlled by applying external magnetic field along the easy axis.In the natural resonance state without external magnetic field,the angle-dependent mode of magnetic resonance exhibits the transition of acoustic or optical resonance modes,and the dependence with the angle between magnetic moment and microwave field was qualitatively obtained as h | cos?|.When the applied magnetic field is close to the saturated field,the angle-dependent resonance mode exhibits only low-frequency acoustic mode,and the resonant frequency of acoustic mode exhibited quasi-isotropic,which provides research ideas and methods for improving the effective utilization of soft magnetic films in microwave integrated circuits. |
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