The invention discloses an iron-based alloy sheet as a material for preparing a magnetic yoke member to build up a magnetic circuit in a hard-disk voice-coil motor as well as a magnetic yoke member made from such a sheet material. With an object to improve the magnetic circuit in respect of compactness and flatness, the iron-based alloy forming the sheet material contains inherent side elements including C, Si, Mn, P, S, Al, O and N each in a specified amount and is characterized by specified values of saturated magnetic flux density, maximum magnetic permeability and coercive force. The iron-based alloy may further contain up to 10% by weight of cobalt and/or one or a combination of adjuvant elements selected from Ti, Zr, Nb, Mo, Cr, V, Ni, W, Ta and B.