A data storage device for use as a portable card, magnetically encodeable card, magnetic credit card or the like is shown. The data storage device includes a substrate having at least one surface. A high density, magnetically coercive material layer is disposed on or is deposited on the substrate for storing magnetic signals. The magnetically coercive material may have an axis of magnetization that is oriented in a predetermined direction relative to the at least one surface of the substrate. A layer of non-magnetically material is disposed on the substrate for defining an exchange break layer. A relatively hard, abradeable protective coating is formed on said magnetic material layer and is selected to have a thickness between a maximum thickness which would materially attenuate magnetic signals passing between the magnetic material layer and a transducer and a minimum thickness enabling said protective coating to be abraded by usage in an ambient natural atmosphere operating environment for removing therefrom a known quantity of the protective coating. The protective coating may comprise one, two or more layers of materials.