Investigation of antiferromagnetic spinwaves at nanoscale in Cr2O3 crystals

Understanding and controlling the interaction between antiferromagnetic (AFM) spin systems and spin currents is a crucial step toward the realization of antiferromagnetic spintronics. Achieving this requires the excitation and detection of spin waves at nanometer length scales, which presents significant experimental challenges and demands fully electrical detection schemes.

In this work, we investigate single-crystalline Cr₂O₃ samples cut along the C- and A-planes. Patterned platinum (Pt) micro- and nanostructures are fabricated on the crystal surfaces using ion milling and lift-off techniques. By applying a magnetic field parallel to the c-axis, we tune the frequency of the left-handed AFM magnons into the gigahertz (GHz) range, enabling a series of spin-dynamic measurements.

Spin pumping experiments are performed by irradiating the crystals with microwaves via a coplanar waveguide, allowing electrical detection of distinct AFM modes, including the left-handed magnon, spin-flop, and Goldstone-like excitations. Furthermore, by driving an electrical current through the Pt structures, we achieve reliable electrical detection of AFM magnons and the spin-flop transition. When a microwave current is applied directly through the Pt nanostructures, spin-torque antiferromagnetic resonance (ST-AFMR) enables the detection of AFM magnons from regions as small as 300 × 300 nm².

These results demonstrate electrical excitation and detection of AFM dynamics at the nanoscale, marking a key step toward functional spin-torque devices based on antiferromagnets. We also report and discuss a yet-unexplained, frequency-dependent anomaly in the spin-current polarization observed in our spin-pumping measurements.