Probing Defect-Induced Magnetism in ZnO Nanoparticles via Small Angle Scattering of Polarized Neutron (SANSPOL) and Soft X-ray Techniques

ZnO nanoparticles exhibit room-temperature ferromagnetism (RTFM), primarily driven by surface oxygen vacancies and structural defects, rather than magnetic doping. In our recent study, we observed magnetic hysteresis at 2 K in both Co- and Al-doped ZnO nanoparticles, with Al-doped ZnO showing magnetic behavior up to 300 K, despite lacking magnetic ions. μSR experiments revealed a quasi-static distribution of internal fields, supporting the presence of shallow donor states, while XPS confirmed oxygen-deficient chemical states. These findings suggest defect-driven magnetism, but the spatial distribution of magnetism remains unresolved. To address this, we propose using polarized Small-Angle Neutron Scattering (SANSPOL) to map magnetization profiles at the nanometer scale, isolating magnetic from nuclear scattering. We hypothesize that ZnO nanoparticles have a magnetically ordered core surrounded by a disordered shell, with the shell's magnetism influenced by surface defects. Measurements will be performed on 3 samples at 3 temperatures (2 K, 100 K, 300 K) and across 7 field points, requiring 6 days of beamtime. Complementary soft X-ray measurements at the BLADE beamline at Diamond Light Source will test whether oxygen vacancies or Zn 3d states are magnetically polarized. This research will deepen our understanding of defect-driven magnetism in semiconductor nanoparticles and inform the design of spin-functional nanomaterials for room-temperature applications.