Effects of thickness on structure and magnetic property of Fe-Y-B thin films

The effects of film thickness on structure and magnetic property of Fe-Y-B were investigated systematically. The 283 nm-thick film was in fully amorphous state, and nanocrystals gradually appeared in the amorphous matrix with increasing thickness. Local roughness at small length scale also rose, indicating the anomalous growth mode. Meanwhile, soft magnetic property and magneto-impedance (MI) effect were significantly enhanced as the film thickness was initially increased. The appearance of nanograins in the soft magnetic matrix may lead to “exchange averaging of the magnetic anisotropy”, decreasing the coercivity and increasing both electrical conductivity and magnetic permeability, which can lessen the skin depth with the increasing thickness and result in the improved MI effect. As the deposition time was further prolonged, MI sensitivity remained almost unchanged in the thicker films, while MI ratio further increased, indicating that MI sensitivity relied more on the coercivity and electrical conductivity, and MI ratio on magnetic permeability and the ratio of skin depth to film thickness, since both the coercivity and electrical conductivity approach the saturated ranges and magnetic permeability continuously increased with thickness.