Bimagnetic Microwires, Magnetic Properties, and High-Frequency Behavior
Bimagnetic microwires are cylindrically multilayered systems consisting of two magnetic metallic microlayers, a cylindrical nucleus, and an external shell, separated by an insulating layer. Such microwires are synthesized by combined quenching and drawing, sputtering, and electrodeposition, and the magnetic configuration of each phase can be suitably tailored to result in soft/soft, soft/hard, or hard/soft biphase microwires. Several families of alloy composition for each phase are considered in this overview: magnetostrictive Fe-based and non-magnetostrictive CoFe-based amorphous alloys for the nucleus and soft FeNi and harder CoNi alloys with polycrystalline character for the shell. The phenomenology of the magnetic behavior of the different microwires under low-frequency applied field is firstly described. Particularly the influence of the thickness of layers and that of thermal annealing are presented. A specific study is performed as a function of the measuring temperature in the range of below (15–300 K) and above (300–1000 K) room temperature. Magnetic and structural phase transitions are determined.
Special attention is paid to the ferromagnetic resonance and microwave absorption experimentally investigated with the help of network analyzer, NA-FMR, as a function of applied field in the frequency range up to 14 GHz and with perturbation cavity at X-band (9.5 GHz) and K-band (69 GHz) under different applied fields. The network analyzer-FMR allows us to conclude the presence of multipeak resonance spectra for soft/soft biphase systems while no absorption is detected for the hard phase. In addition, the observed non-Kittel absorption in bimetallic microwires allows us to confirm the equivalency to a capacitor.
The analysis in perturbation cavity is carried out as a function of the measuring dependence (X-band) where the role of the different contributing phases is determined. A correlation between FMR absorption data with that obtained through NA-FMR is performed. Further analysis at room temperature allows us to conclude the need of magnetic saturation of the hard phase to observe properly its FMR absorption. In addition, the screening effect induced by the external metallic shell on the nucleus is observed.
KeywordsCoNi Shell Biphase System Ferromagnetic Resonance External Shell Metallic Nucleus
Authors thank I. Orue and Luis Lezama (UPV-EHU) for special support. Selected microwave measurements were made at SGIker services UPV-EHU. Work in Madrid has been supported by the Government of Madrid under Project S2013/MIT195, 2850 NANOFRONTMAG-CM. The work done in Prague was partly supported by the Grant Agency of the Czech Republic under the project P102/12/2177.
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