Perpendicular Exchange bias and Coercivity in FeMn/[Pt/Co]₃Films with Various FeMn Thicknesses

An antiferromagnetic FeMn layer was deposited on a [Pt/Co]3 layer that has a perpendicular magnetic anisotropy. The perpendicular exchange bias and coercivity of the [Pt/Co]₃layer with the FeMn thickness and temperature were studied. To induce the perpendicular exchange bias, the films were cooled from 450 to 20 K in a magnetic field of 5 kOe. When the FeMn film was 10-nm thick, the perpendicular exchange bias of [Pt/Co]₃at 20 K was ~200 Oe and its coercivity was ~2000 Oe. The perpendicular exchange bias, coercivity, and exchange-bias blocking temperature showed similar tendencies with varying FeMn thicknesses. The [Pt/Co]₃layers showed a decrease in coercivity after the deposition of the FeMn layer. In addition, the superparamagnetic blocking temperature of [Pt/Co]₃decreased as the FeMn thickness increased. These results suggested that the perpendicular magnetic anisotropy of [Pt/Co]₃was slightly suppressed by the FeMn deposition. Our results provide useful information on controlling the perpendicular exchange bias for future device applications.