Researchers from Tohoku University and Toho University have demonstrated chirality switching by electric current pulses at room temperature in a thin-film MnAu2 helimagnetic conductor. The team also succeeded in detecting the chirality at zero magnetic fields by means of simple transverse resistance measurement utilizing the spin Berry phase in a bilayer device composed of MnAu2 and a spin Hall material Pt. These results may pave the way to helimagnet-based spintronics.
Helimagnetic structures, in which the magnetic moments are spirally ordered, host an internal degree of freedom called chirality corresponding to the handedness of the helix. The chirality seems quite robust against disturbances and is therefore promising for next-generation magnetic memory. While the chirality control was recently achieved by the magnetic field sweep with the application of an electric current at low temperature in a conducting helimagnet, problems such as low working temperature and cumbersome control and detection methods have to be solved in practical applications.
The scientists' new concept for magnet-based memory devices might revolutionize information storage devices owing to their potential for large-scale integration, non-volatility, and high durability.
Magnetic random access memory (MRAM) utilize the magnetization direction of ferromagnetic materials to memorize information. Because of their non-volatility and low energy consumption, spintronic devices will likely play a pivotal role in future information storage components.
However, ferromagnet-based spintronics devices will have to tackle the challenge of ferromagnets generating magnetic fields around them, which affect nearby ferromagnets. In an integrated magnetic device, this results in crosstalk between magnetic bits, which will limit the magnetic memory density.
The research team demonstrated that magnetic materials called helical magnets can be utilized for a magnetic memory device, which should resolve the magnetic field problem. In helical magnets, the directions of the atomic magnetic moments are ordered in a spiral. The right- or left-handedness of the spiral, called chirality, could be utilized to memorize the information. The magnetic fields induced by each atomic magnetic moment cancel each other out, so the helical magnets do not generate any macroscopic magnetic field. "The memory devices based on the handedness of the helimagnets, free from the crosstalk among bits, could pave a new pathway for improving the memory density", says author Hidetoshi Masuda.
The research team demonstrated that the chirality memory can be written and read out at room temperature. They fabricated epitaxial thin films of a room-temperature helimagnet MnAu2 and demonstrated the switching of chirality by the electric current pulses under magnetic fields. Furthermore, they fabricated a bilayer device composed of MnAu2 and Pt (platinum) and demonstrated that the chirality memory can be read out as a resistance change, even without magnetic fields.
"We have uncovered the potential capability of chirality memory in helical magnets for next-generation memory devices; it may offer high-density, non-volatile, and highly stable memory bits", adds Masuda. "This will hopefully lead to future storage devices with ultrahigh information density and high reliability."