Abstract:Recent trends in the development of magnetic sensors are focused on the miniaturization of their size, improvement of their features and on finding of new operating principles based on fundamental studies of new materials. Among new magnetic materials a family of thin wire with reduced dimensions recently gained considerable importance [1,2]. Particularly, studies of giant magneto-impedance (GMI) effect of thin microwires attracted considerable interest [1,2].
We present the results on tailoring of soft magnetic properties and GMI effect in thin microwires at elevated frequencies paying special attention to achievement of low hysteretic high GMI effect in extended frequency range (till 4 GHz). BothGMI ratio and hysteresis loops of Co- rich low magnetostrictive microwires exhibit strong sensitivity to the internal stresses related with the ratio, r, of the metallic nucleus diameter to the total microwire diameter. The hysteresis loops exhibit low coercivity (generally below 10 A/m) with well defined magnetic anisotropy field, Hk. Hk increases when rdecreases. Field dependence of the off-diagonal voltage response measured in pulsed regime (pulsed GMI) exhibits anti-symmetrical shape. Annealing significantly affects the GMI effect of Co- and Fe-rich microwires.
We found, that if the surface anisotropy is not circumferential, then the magnetization and, consequently, the MI curve Z(H) present hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current IB that creates a circumferential bias field HB. On the other hand the magnetic anisotropy of Co and Fe-rich microwires can be tailored by stress or magnetic field annealing. Particularly stress annealed microwires exhibit stress-sensitive GMI effect and hysteretic properties. Varying the time and the temperature of such stress annealing we are able to tailor both magnetic properties and GMI.
Among the other magnetic properties suitable for applications the magnetic bistability and fast Domain Wall (DW) propagation in Fe-rich compositions, considerable magnetoresistace in microwires with granular structure and magnetocaloric effect in Heusler-type microwires should be mentioned. The nanocrystalline structure has been observed in FeSiBCuNb and FeHfBSi microwires.
We manipulated the DW dynamics of microwires through the magnetoelastic anisotropy: decreasing the magnetoelastic energy, Kme,DW velocity increases.
 DC Jiles Acta Materialia 51 (2003)5907
 V. Zhukova, M. Ipatov and A. Zhukov, Sensors 9 (2009) 9216
Short CV: Dr. A.P. Zhukov graduated in 1980 from the Physics-Chemistry Department of the Moscow Steel and Alloys Institute. In 1988 he received Ph.D. degree from the Institute of Solid State Physics (Chernogolovka) of the Russian Academy of Science, in 2010- habilitation in Moscow State University. Present employment: Ikerbasque Research professor at the Department of the Materials Physics of the University of Basque Country, Spain. Current fields of interest: amorphous and nanocrystalline ferromagnetic materials, in particular micro-wires, giant magneto-impedance, giant magnetoresistance, magnetoelastic sensors. He has published more than 300 referred papers in the international journals (total number of citations of A. Zhukov’s papers, updated December 02, 2011: 2162, Citation H-index = 26), edited conference proceedings, chaired III Joint European Magnetic Symposia, few sessions at MMM and Intermag Conferences, gave a number of invited talks at few international conferences, wrote a book “Magnetic properties and applications of ferromagnetic microwires with amorphous and nanocrystalline structure”, few book chapters, articles for the “Enciclopedia of NanoScience and Nanotechnology” and “Enciclopedia of Sensors”. He is a member of several editorial boards and various committees of International Conferences. In 2000 A . Zhukov funded a spin-off company “TAMAG” involved in magnetic microsensors development.