To provide a reluctance sensor having a novel fixation mechanism where the force of a fixed layer moment can be sustained in a micro reluctance sensor.

A fixed layer structure 308 is formed on a seed layer 326 having a surface roughened anisotropically. Magnetic anisotropy is generated in fixed layers 316 and 318 by this anisotropic roughness. Because of the processed seed layer 326, rigid securing of the fixed layer can be sustained without requiring a thick AFM layer and the size of an air gap is reduced. Anisotropic roughness can be formed on the surface of the seed layer 402 by a low-voltage ion mill 404 applied at an inclination angle with respect to the normal to the surface of the seed layer. Ion mill can be applied at 20-100 V by using a nine-region ion extraction grid. Angle of ion mill is 20-80° with respect to the normal to the surface of the seed layer.