Ortho-atomic projector assisted DFT+U study of room temperature Ferro- and antiferromagnetic Mn-doped TiO₂ diluted magnetic semiconductor

Abstract

Using ortho-atomic Hubbard-corrected density functional theory, we present magnetic properties, ferromagnetic transition temperature Tc, Neel temperature TN, electronic structure, structural formation energy, and crystal structure of anatase (Ti16−xMnxO32 for x = 1,2,3,4 and 6). According to the calculated formation energy, an oxygen-rich condition is more structurally stable than a Ti-rich situation. The geometric and lattice parameter optimization result indicates that Mn2+ exists in the system. In addition, when Mn is substituted in the system, some of the bonds that connect oxygen with the Mn ion are broken, and the bond lengths show variation; this results in defects, which cause the formation of oxygen vacancies that enhance the both ferromagnetic and antiferromagnetic properties of the system. According to the structure of electronic bands and PDOS analysis, 2p and 3d hybridization leads to a decrease in the edge of the CB and an increase in the edge of the VB, narrowing the bandgap from 3.23 eV to 2.21 eV(for 4.17 % of Mn), 2.13 eV (for 8.33 % of Mn) and 1.69 eV ( for 12.5% of Mn). Results also showed that both ferromagnetic and antiferromagnetic properties are energetically favored. Furthermore, the material exhibits antiferromagnetic with predicted TN to be 804.13 K for small concentration of Mn dopant (for 4.17 % of Mn), which is higher than room temperature. In contrast, the calculated ferromagnetic temperature (Tc) was increased from 255.42 K (for 8.33 % of Mn) to 385.63 K (for 12.5 % of Mn), most likely as a cause for bound magnetic polarons (BMPs) production. Result also reveals, oxygen vacancy for the relaxed pristine (Ti16O31) a non-zero magnetic moment and total magnetization 2.00 μB which is observed as a result of ortho-atomic projector. The present findings suggest that, TiO2 could be tailored through doping and oxygen vacancy for versatile spintronic applications, in consistent with previous experimental results.

Experimental Studies on TiO2 NT with Metal Dopants through Co-Precipitation, Sol–Gel, Hydrothermal Scheme and Corresponding Computational Molecular Evaluations

“…The structure simulation and mechanism analysis have demonstrated the co-doped TiO 2 gas sensor's improved characteristics and excellent gas-sensing capabilities at ambient temperature [131]. An ab initio study of the systems Ti 1−x R x O 2 (R = Mn, Fe, Co, Ni, Cu for various concentrations of substitutional impurities) in the rutile structure revealed that magnetic moments are present in Fe, Co, and Mn but not in Cu or Ni [132,133]. These calculations reveal an essential fact: doping reduces the energy required for vacancies to occur, resulting in doped systems having more vacancies than undoped systems.…”

“…All dopants significantly stabilize anatase compared to the rutile phase, indicating that the conversion of anatase to rutile is prevented in such systems, with the dopants arranged in the order F > Si > Fe > Al according to the strength of anatase stabilization. The Al and Fe dopants act as shallow acceptors, with charge balance achieved by the formation of mobile charge carriers rather than anion vacancies [133,134,[137][138][139]. In Si-TiO 2 , the Si dopant acts as an inhibitor of the phase transformation from anatase to rutile; in Al-TiO 2 , the Al dopants act as weak inhibitors of the phase transformation from anatase to rutile, and the Fe dopants act as inhibitors of the phase transformation in TiO 2 [133].…”

“…The Al and Fe dopants act as shallow acceptors, with charge balance achieved by the formation of mobile charge carriers rather than anion vacancies [133,134,[137][138][139]. In Si-TiO 2 , the Si dopant acts as an inhibitor of the phase transformation from anatase to rutile; in Al-TiO 2 , the Al dopants act as weak inhibitors of the phase transformation from anatase to rutile, and the Fe dopants act as inhibitors of the phase transformation in TiO 2 [133]. TiO 2 (Li-TiO 2 ) have been studied by DFT [140].…”

First-Principles Study of the Quasi-Particle and Excitonic Effect in o-BC2N: The GW + BSE Study

“…Semiempirical approaches, such as DFT + U [24][25][26] and hybrid density functionals (HSE) [27], which were originally developed to improve the description of the ground-state energies of small molecules, have been shown to improve the description of bandgaps in semiconductor systems [28]. Furthermore, the prediction of quasi-particles necessitates the use of many-body techniques, such as the many-body perturbation theory (MBPT) based on the GW method, to describe the energies of solid-state electronic excitation spectra.…”