Tunable spin-flop transition in artificial ferrimagnets

Spin-flop transition (SFT) consists in a jump-like reversal of antiferromagnetic (AF) lattice into a noncollinear state when the magnetic field increases above the critical value. Potentially the SFT can be utilized in many applications of a rapidly developing AF spintronics. However, the difficulty of using them in conventional antiferromagnets lies in (a) too large switching magnetic fields (b) the need for presence of a magnetic anisotropy, and (c) requirement to apply magnetic field along the correspondent anisotropy axis. In this work we propose to use artificial ferrimagnets (FEMs) in which the SFT occurs without anisotropy and the transition field can be lowered by adjusting exchange coupling in the structure. This is proved by experiment on artificial Fe-Gd FEMs where usage of Pd spacers allowed us to suppress the transition field by two orders of magnitude.