Extraordinary magnetic field response by diluting spin — Demonstration using both theory and experiments by the University of Tokyo

Assistant Professor Hidemaro Suwa of the School of Science at the University of Tokyo, in collaboration with research groups from the University of Tennessee, Chinese Academy of Sciences, Argonne National Laboratory, Brookhaven National Laboratory, Oklahoma State University, Charles University and Dublin City University, has theoretically and experimentally demonstrated a mechanism to control spin anisotropy and obtain an extraordinary magnetic field response by diluting antiferromagnetic spin. The results were published in Nano Letters.

The research group has theoretically shown that an effectively spin-isotropic strong magnetic field response can be achieved when the dilution rate exceeds a threshold in a 2D system of spin-anisotropic antiferromagnets. Based on this theory, the team synthesized thin films with various site dilution rates by substituting spin-bearing iridium with spin-free titanium in a superlattice structure [(SrIrO₃)₁/(SrTiO₃)₂] with strong two-dimensionality. This material exhibits a slightly tilted antiferromagnetic order at low temperatures.

The team determined the antiferromagnetic order parameter's magnetic field-temperature dependence using resonant X-ray magnetic scattering. At a 50% dilution rate, they observed the extraordinary magnetic field response. Specifically, at a magnetic field of 0.5 Tesla, which corresponds to a mere 0.1% of the spin interaction energy (50 meV), the antiferromagnetic transition temperature increased by as much as 600%. The dilution rates of 0,15 and 35% may be accounted for by an anisotropic model; however, the 50% dilution rate aligns well with theoretical calculations using an isotropic model, resulting in a significant increase in the transition temperature.

The group theoretically clarified the mechanism of spin-isotropic magnetic field response owing to dilution. By integrating the mechanism with the quantum Monte Carlo calculations, the group quantitatively explained the experimentally observed increase in the transition temperature. The loss of anisotropy owing to dilution revealed in this study can be applied to various materials and is expected to lead to efficient spin manipulation in future antiferromagnetic spintronics.

Journal Information
Publication: Nano Letters
Title: Extraordinary Magnetic Response of an Anisotropic 2D Antiferromagnet via Site Dilution
DOI: 10.1021/acs.nanolett.3c02470