Thermal effects on delta-M measurements in magnetic thin films

Thermal effects on delta-M curves have been studied in a series of CoCrPtB thin films. Film thicknesses ranged from 5 nm to 50 nm and K/sub u/V/k/sub B/T values ranged from 29 to 132. Delta-M curves were measured as a function of field step, wait time at each field step, and measuring conditions. If dc-demagnetization remanence (DCD) curves are measured by applying a saturating field before each reverse field, then the delta-M curves depend on field step for all films and on wait time for the film with the smallest K/sub u/V/k/sub B/T. At small field steps, the field step dependence is approximately logarithmic and the rate is approximately the same as the remanent viscosity coefficient. If a saturating field Is applied only at the beginning of the DCD measurement sequence, the field step and wait time dependences are essentially eliminated. For fixed field step and waiting time, the area under the delta-M curve normalized to the remanent coercivity increases linearly with k/sub B/T/K/sub u/V when the repeat saturation method is used. The dependence on k/sub B/T/K/sub u/V is largely eliminated if there is no repeat saturation field.