Fabrication And Characterization Of Noise Suppressors Based On Ferromagnetic Nanowires

Due to the widely application of the high-frequency electromagnetic devices inour daily life or the industry and the rapid development of large-scale integratedcircuits, the electromagnetic interference of the electrical systems and electronicdevices has become an increasingly serious problem. It has become more and moreimportant for the researchers to synthesize a high-performance noise suppressor,which can absorb high-frequency electromagnetic noise. The ferromagneticnanowires have higher permeability and higher ferromagnetic resonance frequenciesthan the conventional ferrites or magnetic thin films. Noise suppressors based on theferromagnetic nanowires have better noise absorption properties. Their workingfrequencies can be above20GHz and it is easy for us to achieve the miniaturizationand integration. Multilayered magnetic nanowire arrays have special magneticproperties and can enhance the functionalities of the noise suppressors.In our study, the Co/Au multilayered nanowires with the diameters of80nm or200nm were successfully electrodeposited into the porous anodic aluminum oxide(AAO) templates in a single bath. The structure and magnetic property of the Co/Aunanowires with various Co-layer thicknesses were studies. The pure Co nanowireswere also electrodeposited with the same method for reference. The dark segmentsalternate with the bright segments in the Co/Au multilayered nanowire could beobserved through the transmission electron microscopy. X-ray diffraction spectrarevealed that Au layers and Co-rich layers exhibited an fcc (111) texture and an hcpstructure, respectively. Hysteresis loops measured by vibrating sample magnetometrydemonstrated that the Co/Au multilayered nanowires with the diameters of80nm hada strong magnetic anisotropy along the nanowires and the magnetic anisotropybecame larger as the Co-layer thickness increased. The Co/Au multilayerednanowires with the diameters of200nm had a strong magnetic anisotropyperpendicular to the nanowires.The coplanar waveguide (CPW) transmission lines were patterned on the AAO templates filled with the pure Co, Co-Ni alloy or Co/Au nanowires. The transmissioncoefficient S21and reflection coefficient S11of the devices were measured by thevector network analyzer. The reflection could be reduced by adjusting the width ofthe signal line to achieve the impedance matching. The noise suppressors based onthe pure Co nanowires showed a strong absorption peak at22~27GHz due to theferromagnetic resonance. Similarly, S21of the noise suppressors based on the Co-Nialloy nanowires had a broadband absorption from23GHz to40GHz. Moreinterestingly, S21of the noise suppressors based on the Co/Au multilayered nanowiresshowed a dual-band absorption phenomenon because of the ferromagnetic resonanceof the nanowires and the periodicity of the magnetic/nonmagnetic nanostructure. Thefrequencies of the two absorption peaks were24~25GHz and36~38GHz indicatingthat the working frequency of the microwave devices could be beyond20GHz.