The lower core layer 7 is formed in approximately constant thickness at the portion confronting the upper core layer so that its thickness gradually reduces toward its side edge. Therefore, the thickness of the layer of the non-magnetic material 8 formed on the lower core layer 7 becomes uniform, stabilizing the coil layer formed thereon. An excellent material of soft magnetic materials can be used since the lower core layer 7 is formed by sputtering, enabling to record at a high frequency.