Demagnetising field reduction in keepered media

We have used a comparative study of time decay of magnetisation and thermal loss of signal in keepered and unkeepered recording media to obtain a meas urement of the effective reduction in demagnetising field resulting from th e keeper. By measuring magnetic viscosity in the recording layer of a CoCrT a media we have determined the loss of magnetisation per decade of time, ov er a wide range of fields around the coercivity. Measurements of recorded s ignal thermal loss effects in the same media both with and without a keeper layer exhibit a significant reduction in the thermal loss from 2.8% to 1.1 % per decade of time due to the keeper. Comparison with the bulk time depen dence data shows that this corresponds to a reduction in the effective dema gnetising field from 1786 to 1493 Oe which moves the demagnetising field aw ay from the edge of the switching field distribution onto the flat portion of the hysteresis loop. (C) 1999 Elsevier Science B.V. All rights reserved.