Observation of room temperature d0 ferromagnetism, bandgap narrowing, zero dielectric loss, dielectric enhancement in highly transparent p-type Na-doped rutile TiO2 compounds for spintronics applications

Abstract

The Na-doped TiO2 compounds, i.e Ti1−xNaxO20≤x≤0.12 were synthesized via the solid-state synthesis method. The formation of single rutile phase with tetragonal structure was identified through the structural study by recording the XRD patterns. The analyses of the XRD patterns further indicate that Na+ ions are likely being substituted at the interstitial site of Ti4+ ions. The microstructural study using SEM revealed the homogeneous morphology of all compounds, with the particle size in the range of 1–2 μm. The room temperature magnetization versus field measurement reveals a ferromagnetic behavior for all Na-doped compounds with coercivity values ranging from 100 to 930 Oe. The saturation magnetization was observed to be maximum for Ti0.97Na0.03O2 compound but thereafter it decreases. According to optical property measurements, the bandgap reduces from 2.94 to 2.71 eV as the concentration of Na doping increases. The maximum transmittance value 91% was noted for Ti0.97Na0.03O2 compound. The Hall effect measurements indicate that the carrier concentration of all Na-doped TiO2 ranged from 1.077×1015 to 7.579×1015/cm3, and it grew monotonically with the increase of Na-doping concentration. The value of the ac conductivity and dielectric constant were observed to enhance with increasing Na-doping concentration; indicating that transport occurs via hopping of the charge carrier. Further, the dielectric properties observation reveals lossless nature in the produced sample, which suggests that this material could be employed in high-frequency optoelectronic devices.