Lattice defect-formulated ferromagnetism and UV photo-response in pure and Nd, Sm substituted ZnO thin films

The induction of charge and spin in diluted magnetic semiconductor ZnO is explored for spintronic devices and its wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) exhibit potential in UV photodetectors. We reported the ferromagnetic and optical properties of pure ZnO, Zn_0.97Nd_0.03O and Zn_0.97Sm_0.03O thin films. These thin films were synthesized by a metallo-organic decomposition method and annealed at 500 °C for 7 h. Rietveld refinement of the XRD data results in a wurtzite ZnO structure with Nd, Sm doping. The dopants and nanoparticle size are responsible for wurtzite structural deformation, inducing lattice strain effect, which may influence the band gap energy and high-T_C ferromagnetism of ZnO. The average size of ZnO nanoparticles with Nd, Sm doping is 10 nm, confirmed with atomic force microscopy. The Raman spectra confirm the wurtzite structure of ZnO with crystalline quality and lattice defect formation with dopant Nd, Sm ions. A near-band-edge emission due to band gap energy is evaluated with photoluminescence spectra, which also involved multiple visible emissions due to oxygen vacancies. The oxygen vacancies-mediated magnetic interactions impart room temperature ferromagnetism in pure ZnO which is enhanced with Nd, Sm doping. The electron paramagnetic resonance spectra revealed the effects of defects and unpaired electrons responsible for observed room temperature ferromagnetism. The zero field cooling and field cooling magnetic measurements include antiferromagnetic interactions without any spin-glass formation. The observed ferromagnetism also correlates with first principle calculations reported for Nd, Sm-doped ZnO and suggests long-range ferromagnetic ordering attributed to defect carriers. The Nd, Sm doping into ZnO thin films significantly enhances absorption in the UV region and suggests its usability for UV detectors. Under UV irradiation (λ = 325 nm), the value of photocurrent in Nd, Sm:ZnO thin films is highly enhanced for possible use in UV sensors.

dz2 orbital-mediated bound magnetic polarons in ferromagnetic Ce-doped BaTiO3 nanoparticles and their enriched two-photon absorption cross-section

The enriched ferromagnetism and two-photon absorption (TPA) cross-section of perovskite BaTiO3 nanoparticles are indispensable for magnetic and optical data storage applications. In this work, hydrothermally synthesized Ce-doped BaTiO3 nanoparticles exhibited the maximum room temperature ferromagnetism (4.26 × 10-3 emu g-1) at 4 mol% due to the increase in oxygen vacancies, as evidenced by X-ray photoelectron and electron spin resonance spectroscopy and density functional theory (DFT) calculations. Hence, the oxygen vacancy-constituted bound magnetic polaron (BMP) model was invoked to explain the enhancement in ferromagnetism. The BMP theoretical model indicated an increase in BMP magnetization (M0, 3.0 to 4.8 × 10-3 emu g-1) and true spontaneous moment per BMP (meff, 4 to 9.88 × 10-4 emu) upon Ce doping. DFT calculations showed that BMPs mediate via the Ti dz2 orbitals, leading to ferromagnetism. Besides, it is known that the magnetic moment induced by Ce at the Ba site is higher than Ce at the Ti site in the presence of oxygen vacancies. The open aperture Z-scan technique displayed the highest TPA coefficient, β (7.08 × 10-10 m W-1), and TPA cross-section, σTPA (455 × 104 GM), at 4 mol% of Ce as a result of the robust TPA-induced excited state absorption. The large σTPA is attributed to the longer excited state lifetime, τ (7.63 ns), of the charge carriers created by oxygen vacancies and Ce ions, which encounter several electronic transitions in the excited sub-states.

Tailoring the multiferroic behavior in BiFeO3 nanostructures by Pb doping

Substituting Pb²⁺ for Bi³⁺ in BiFeO₃ can induce lattice distortions and structural transitions to tune the lone-pair activity for ferroelectricity and neutralized oxygen vacancies to valence Fe²⁺/Fe³⁺ ions for ferromagnetism.

Realizing ferromagnetic ordering in SnO2 and ZnO nanostructures with Fe, Co, Ce ions

The dopants Co and Ce in SnO₂ nanostructures favour room temperature ferromagnetism, whereas in ZnO, the dopants involve in antiferromagnetic interactions at room temperature.