Negative Coercivity and Spin Configuration in Ni/TbFeCo/Ni Trilayers

Hysteresis loops of Ni/TbFeCo/Ni deposited by sputtering are presented and discussed. The magnetization easy axis of TbFeCo layer is perpendicular to the films plane. Trilayers with Ni thickness less than 3 nm show lower magnetization at 24 kOe, which is attributed to the antiferromagnetic exchange coupling. Trilayer with Ni layer thickness higher than 5 nm show negative coercivity in the perpendicular direction. Micromagnetic simulations suggest that the negative coercivity is contributed by the strong antiferromagnetic exchange coupling in the interface between the TbFeCo and Ni layer. Antiferromagnetic exchange coupling tend to align the magnetization of the soft Ni layer antiparallel to the applied field.