Effect of thermal treatment on high-frequency magneto-impedance in ferromagnetic/Cu/ferromagnetic trilayers

Abstract Ferromagnetic/Cu/ferromagnetic trilayers (FM/Cu/FM) have been produced by sputtering (FM = CoFeSiB or FeSiB, thickness 80–500 nm). The Cu layer, longer than the two FM layers, is connected to a strip line attached to a network analyzer (frequency interval 30 kHz–6 GHz). The variation of the characteristic impedance of the line with a static magnetic defines the giant magneto-impedance (GMI) ratio. Trilayers have been annealed in furnace, with and without a magnetic field (aimed to induce a magnetic anisotropy). The effect on GMI of the FM material composition, thickness and annealing has been studied. In general, transverse annealing improves the GMI response of the device, whereas longitudinal annealing on CoFeSiB-based trilayers does not improve the GMI response, but reduces the field value at which peak GMI effect is observed.