Narrow Band Gap and Room-temperature Ferromagnetism in KNb1-xFexO3-δ

We have investigated the structure, optical and magnetic properties of ferroelectric KNb1-xFe2O3-δ （x=0, 0.01, 0.03, 0.05, 0.10, 0.15, 0.20, 0.25） synthesized by a traditional solid-state reaction method. According to the X-ray diffraction and the results of Rietveld refinement, all the samples maintain orthorhombic distorted perovskite structures with Amm2 space group without any secondary phase, suggesting the well incorporation of Fe ions into the KNbO3 matrix. With the increase of Fe concentration, the band gap of each sample is decreased gradually, which is much smaller than the 3.18 eV band gap of pure KNbO3. Through X-ray photoelectron spectrum analysis, the increased density of oxygen vacancy and Fe ions may be responsible for the observed decrease in band gap. Compared with the pure KNbO3, Fe doped samples exhibit room-temperature weak ferromagnetism. The ferromagnetism in KNb1-xFexO3-δ with low-concentration dopants （x=0.01-0.10） can be attributed to the bound magnetic polaron mediated exchange. The enhancement of magnetism for the high-concentration （x=0.10-0.20） doped samples may arise from the further increase of magnetic Fe ions.

Defect induced room-temperature ferromagnetism and enhanced photocatalytic activity in Ni-doped ZnO synthesized by electrodeposition

Zn0.90Ni0.10O nanoparticles have been synthesized by single-bath two-electrode electrodeposition at constant voltage. X-ray diffraction, UV vis and photoluminescence studies reveal that a single-phase polycrystalline hcp wurtzite crystal structure of ZnO is evolved. The material consists of a large number of defects such as oxygen vacancy (Ov) and zinc interstitial (Zi). The magnetization study reveals that the sample exhibits room-temperature global ferromagnetism and the ferromagnetic ordering seems to be defect induced via bound magnetic polaron mechanism, and double exchange is also expected to have played role. Interesting optoelectronic properties have been found in the synthesized sample and the material seems to be a potential candidate to be used as a UV sensor. Such a transition metal doped ZnO based dilute magnetic semiconducting system exhibiting room-temperature ferromagnetism is likely to be first of its kind in the sense that such materials have not yet been reported to be synthesized by the simple method of electrodeposition to the best of our knowledge on the basis of ample literature review.

A Physical Insight into the Origin of the Corrections to the Magnetic Moment of Free and Bound Electron

The main goal of the present work is a unitary approach of the physical origin of the corrections to the magnetic moment of free and bound electron. Based on this approach, estimations of lowest order corrections were easily obtained. In the non-relativistic limit, the Dirac electron appears as a distribution of charge and current extended over a region of linear dimension of the order of Compton wavelength, which generates its magnetic moment. The e.m. mass (self-energy) of electron outside this region does not participate to this internal dynamics, and consequently does not contribute to the mass term in the formula of the magnetic moment. This is the physical origin of the small increase of the magnetic moment of free electron compared to the value given by Dirac equation. We give arguments that this physical interpretation is self-consistent with the QED approach. The bound electron being localized, it has kinetic energy which means a mass increase from a relativistic point of view, which determines a magnetic moment decrease (relativistic Breit correction). On the other hand, the e.m. mass of electron decreases at the formation of the bound state due to coulomb interaction with the nucleus. We estimated this e.m. mass decrease of bound electron only in its internal dynamics region, and from it the corresponding increase of the magnetic moment (QED correction). The corrections to the mass value are at the origin of the lowest order corrections to the magnetic moment of free and bound electron.

Effect of Cu Co-doping on the Magnetism of Zn_(0.95)Co_(0.05)O Films

Zno.95-xCoo.05CuxO （atomic ratio, x = 0-8%） thin films are fabricated on Si（lll） substrate by reactive magnetron sputtering method. Detailed characterizations indicate that the doped Cu ions substitute the Zn2＋ ions in ZnO lattice. The doped Cu ions are in ＋1 and ＋2 mixture valent state. The ferromagnetism of the Zno.95-xCoo.o5CuxO film increases gradually with the increase of the Cu＋ ion concentration till x = 6%, but decreases for higher Cu concentration. Experimental results indicate that the increase of ferromagnetism is not owing to the magnetic contribution of Cu＋ ions themselves, but owing to the enhancement of magnetic interaction between Co2＋ ions, which suggests that p-type doping of Cu＋ ions plays an important role in mediating the ferromagnetic coupling between Co ions.

Effect of Sn-doping on the structural,electrical and magnetic properties of(In_(0.95-x)Sn_xFe_(0.05))_2O_3 films

Room-temperature ferromagnetism was observed in （In0.95-xSnxFe0.05）203 （x = 0-0.09） films deposited by pulsed laser deposition. XRD results give a direct proof that both Sn and Fe ions have been incorporated into the In2O3 lattice. The carrier concentration in the films is obviously increased by the Sn-doping, while the ferromagnetic properties are rarely changed. We think that in our Fe-doped In2O3 films, the oxygen vacancy-related bound magnetic polaron model, rather than the carrier-mediated RKKY coupling, is the main mechanism for the observed ferromagnetism.