Small Changes Yield Major Advances in Materials Research

Small Changes Yield Major Advances in Materials Research
by Riko Seibo
Tokyo, Japan (SPX) Jun 27, 2024

A minor adjustment can lead to significant advancements, as demonstrated by researchers at Pohang University of Science and Technology (POSTECH). The team developed a material known as "spin-orbit torque (SOT)," gaining attention in the field of next-generation DRAM memory.

Led by Professor Daesu Lee and PhD candidate Yongjoo Jo from the Department of Physics, alongside Professor Si-Young Choi from the Department of Materials Science and Engineering, the POSTECH researchers achieved efficient field-free SOT magnetization switching through precise atomic-level control of composite oxides. Their findings were published in the international journal Nano Letters.

SOT results from the interplay between the spin (magnetic property) and motion (electrical property) of electrons, allowing control over magnetic states via spin movement when current flows. Utilizing magnetic information rather than electrical information reduces memory power consumption, benefiting non-volatile memory which retains data without power. Researchers are exploring various materials, particularly those exhibiting both magnetism and the "spin-Hall effect." The quest for efficient SOT-based magnetization switching is of great interest, although challenges persist, such as opposing spin currents within a single layer cancelling each other out.

The POSTECH team addressed this issue by modifying the material's structure. They synthesized strontium ruthenate (SrRuO3), a complex oxide known for its magnetism and spin-Hall effects, with asymmetric spin-Hall effects on the top and bottom surface layers by finely adjusting the atomic lattice structure. This created an imbalance in the spin-Hall effect, allowing specific direction control of magnetization.

Utilizing this method, the team achieved efficient magnetization switching without a magnetic field. Incorporating SOT into a SrRuO3-based device, they reoriented the magnetic domain using only electric current for data writing and reading. The resulting memory device exhibited the highest efficiency (2 to 130 times greater) and lowest power consumption (2 to 30 times lower) compared to any known single-layer, field-free system to date. This was accomplished without a magnetic field, maintaining the conventional properties of SrRuO3 from previous studies.

Professor Daesu Lee of POSTECH stated, "The asymmetric SrRuO3 synthesized by the team is a crucial platform for studying the interaction between ferromagnetism and the spin-Hall effect." He added, "We look forward to further research to uncover new SOT mechanisms and develop highly efficient, room-temperature, single-phase SOT materials."

Research Report:Field-Free Spin-Orbit Torque Magnetization Switching in a Single-Phase Ferromagnetic and Spin Hall Oxide