Unidirectional anisotropy in exchange coupled NiFe/FeMn system for thin NiFe films

The unidirectional exchange anisotropy field H/sub ex/ was investigated in NiFe/FeMn films. It was found that the H/sub ex/ is proportional to t/sub NiFe//sup -1.2/ for 30 /spl Aring//spl les/t/sub NiFe//spl les/400 /spl Aring/ where t/sub NiFe/ is the NiFe film thickness. For t/sub NiFe/=30 /spl Aring/, H/sub ex/ was measured to be 800 Oe in some samples. NiFe/FeMn structures on alumina underlayers were also studied; their presence reduces the strength of the anisotropy significantly.