Room temperature ferromagnetism in Mn-doped TiO2 nanopillar matrices

• Ferromagnetic (FM) Mn-doped TiO2 nanopillars were synthesized by ALD.
• Anatase nanopillars form by deposition at 400 °C with no catalyst or seed layer.
• Nanopillars (Mn-doped) enhance the coercive field and saturation magnetization.
• Nanopillars promote congregation of bound magnetic polarons near grain boundaries.
• Such effects are not as pronounced with conventional columnar grains.

Diluted magnetic semiconductors have attracted considerable attention for potential applications in spintronics. Morphology and microstructure exert strong, but complicated, effects upon ferromagnetic behavior. To partially unravel such effects, the present work compares room temperature ferromagnetism (RTFM) in Mn-doped anatase TiO2 films synthesized by two different atomic layer deposition protocols, leading to either nanopillars or more conventional columnar grains. RTFM is largely unaffected by this difference for undoped material, but nanopillaring greatly increases both the coercive field (100 Oe) and saturation magnetization (14–21 emu/cm3) for Mn doping up to 2.7 at%. Nanopillaring seems to enhance the congregation of defect-related bound magnetic polarons near grain boundaries, thereby increasing RTFM.