High sensitive detection of susceptibility modulation by LC resonator embedded with ferromagnetic multilayer

In the present study, high sensitive detection of the reversible susceptibility modulation in the magnetic thin film was performed by an LC circuit resonant technique. A flat pick-up coil with the inductance of 0.80 μH and a capacitance of 100 pF construct the LC resonant circuit. The reversible susceptibility χ of the magnetic thin film, embedded in the pick-up coil, was measured with a sinusoidal exciting field (H). The out put signal was modulated by applying an orthogonal bias field (H_b). A multilayer sample of [NiFe(100 nm)/Cu(10 nm)₂₀ exhibits the most sensitive modulation effect among the fabricated samples. That is, the resonant frequency f_r was decreased from 11.58 MHz (H_b = 0 Oe) to 8.22 MHz (H_b = 7 Oe) at H_ex = 2.5 mOe, suggesting the marked increase of χ. The value of H_b, which minimizes f _r, is comparable to the anisotropy field. Thus, the observed drastic increase of χ can be associated with the compensation of the anisotropy with H_b, as confirmed from the theoretical prediction. The practical out put voltage change of 55%/Oe was realized for the fabricated resonator.