Control of Bistable Antiferromagnetic States for Spintronics

Scientists from MPI CPfS, in collaboration with colleagues from National Yang Ming Chiao Tung University, National Cheng Kung University, and National Synchrotron Radiation Research Center in Taiwan as well as from Hiroshima University in Japan, have used strained engineering on multiferroic BiFeO₃ (BFO) thin films, to fabricate bistable antiferromagnetic states at room temperature for the first time.

These two antiferromagnetic states are non-volatile and very close to each other in energy, which was verified by soft x-ray linear dichroism spectroscopy. Moreover, these two non-volatile antiferromagnetic states can be reversibly switched by a moderate magnetic field and a non-contact optical approach. The team stressed that the conductivity of the two antiferromagnetic domains is drastically different.

Nowadays, spintronic devices for magnetic memory and information processing are mainly based on the bistability of ordered spin states in ferromagnets. The use of ferromagnetic units, however, sets in a bottleneck for high-density memory integration and information retention due to its ferromagnetic stray field from the neighbors and its vulnerability to the magnetic field perturbations, respectively. All these could be changed and improved by replacing ferromagnets with antiferromagnets as the units. Moreover, the switching speed attainable in antiferromagnets is expected to far exceed those of ferromagnets. The use of antiferromagnetic units requires manipulatable and non-volatile antiferromagnetic bistable states at ambient temperature, however, those states are rarely reported in materials. Furthermore, the insensibility or even invisibility of antiferromagnetic character (i.e. zero net magnetic moment) to external stimuli poses great challenges in controlling and detecting antiferromagnetic states.

In this new work, the team effectually discovered two bistable and reversibly controllable antiferromagnetic states in strained BiFeO₃ (BFO) films. These two non-volatile antiferromagnetic states are successfully patterned with a non-contact approach combining both optical and magnetic methods. The written antiferromagnetic pattern is electrically readable with at least 30% signal difference. This work could lead to an efficient route toward practical applications of antiferromagnetic spintronics.