GMI in Nanostructured FeNi/Ti Multilayers With Different Thicknesses of the Magnetic Layers

Nanostructured multilayers are proposed as a competitive alternative to magnetoimpedance (MI) thick films. However, the effect of the thickness of the magnetic layers on the properties of MI multilayers is still unclear. To perform a systematic study, three multilayered structures consisting of magnetic
${\rm Fe}_{20}{\rm Ni}_{80}$
layers and nonmagnetic Ti layers were prepared by sputtering. In each structure, FeNi layers have different thickness (25, 50, and 100 nm) keeping the same total thickness. Magnetic measurements and magnetic domain structure observations were used for the characterization of the samples. The MI of FeNi/Ti- based multilayers was evaluated in terms of the magnitude of the impedance variations and its sensitivity with respect to the applied magnetic field. The results show that the multilayer with 50 nm FeNi layers has a slightly better properties than the sample with a 100 nm FeNi layers, while the sample with a 25 nm thick FeNi layers performs considerably worse. The sample
$[{\rm FeNi}(50\ {\rm nm})/{\rm Ti}(6\ {\rm nm})]_{7}/{\rm FeNi}(50\ {\rm nm})$
displays a MI ratio of 24% at 200 MHz and a sensitivity of 135
$\%{\rm kAm}^{-1}$
at 140 MHz.