Micromagnetic behavior and recording performance in high density 5 Gb/in.2 CoCrPtTa medium

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Abstract
Micromagnetic studies of the magnetization process in high density 5 Gb/in.2 CoCrPtTa and 0.8 Gb/in.2 CoCrTa media were carried out in conjunction with recording performance measurements. The maximum value of the δM curves measured at room temperature and at 373 K is smaller for CoCrPtTa compared to CoCrTa which indicates lesser intergranular exchange coupling in the quaternary medium. At room temperature, the Barkhausen volume V*, which is the smallest switching unit in magnetization reversal, corresponds approximately to one grain for CoCrPtTa but to three to four grains for CoCrTa. These results are consistent with the lower media noise found for CoCrPtTa especially at high bit densities. A decrease in V* to the size of one grain for CoCrTa is observed for temperatures below 200 K. The reduced intergranular exchange is confirmed by δM measurements at 77 K. Low coupling, however, leads to low values of Mr which leads to a reduction in the reading signal. The value of Mr for CoCrTa at 77 K is 60% greater than that of CoCrPtTa at room temperature despite the reduced exchange coupling indicating that larger values of Mr can still be achieved while confining the switching volume to no more than a grain.