An apparatus according to one embodiment includes at least one write transducer, and a plurality of detector structures positioned in an array. Each of the detector structures includes a pair of conductive layers separated by an insulating material. None of the detector structures include an operable reader for reading data from a magnetic medium. A computer-implemented method according to one embodiment includes monitoring a resistance value of each of a plurality of detector structures positioned in an array, and detecting a change in a resistance value of at least one of the detector structures for identifying a defect on a magnetic medium. Each of the detector structures include a pair of conductive layers separated by an insulating material. None of the detector structures include an operable reader for reading data from a magnetic medium.