Observation of room temperature ferromagnetism in pure La2O3 nanoparticles

In this paper, we report the observation of intrinsic room temperature ferromagnetism in pure La₂O₃ nanoparticles. Magnetism measurement indicates that all of the samples exhibit room temperature ferromagnetism and the saturation magnetization for the samples decreases with the increase in annealing temperature from 700 to 1,000 °C. X-ray photoelectron spectroscopy identifies the presence of oxygen vacancies in the La₂O₃ nanoparticles. The fitting results of the O 1s spectrum indicate that the variation of the oxygen vacancy concentration is in complete agreement with the change of the saturation magnetization. It is also found that the saturation magnetization of the La₂O₃ nanoparticles can be tuned by post-annealing in argon or oxygen atmosphere. These results suggest that the oxygen vacancies are largely responsible for the room temperature ferromagnetism in pure La₂O₃ nanoparticles.     

Enhanced room temperature ferromagnetism and photoluminescence behavior of Cu-doped ZnO co-doped with Mn

Cu, Mn co-doped ZnO nanoparticles were successfully synthesized by the sol–gel technique. XRD pattern described that Mn-doping did not affect the hexagonal wurtzite structure of the samples and no secondary phases were found. The reduced crystallite size at Mn=2% is due to the suppression of grain surface growth by foreign impurity. The enhancement of crystal size after Mn=2% is due to the expansion of lattice volume produced by the distortion around the dopant ion. The better dielectric constant and conductivity noticed at Mn=2% are explained by charge carrier density and crystallite size. The suppression of broad UV band by Mn-doping is discussed based on the generation of non-radiative recombination centers. Hysteresis loop showed the clear room temperature ferromagnetism in all the samples and the magnetization increased with Mn-doping. Better electrical and magnetic behavior of Zn_0.94Cu_0.04Mn_0.02O sample is suggested for effective opto-magnetic devices.     

Fe doping induced enhancement in room temperature ferromagnetism and selective cytotoxicity of CeO2 nanoparticles

In the present study, structural, optical, magnetic properties as well as cytotoxicity of undoped and Fe doped Ceria (CeO₂) nanoparticles synthesized by simple soft chemical method have been reported. SEM and XRD results have shown that the synthesized samples are comprised of ultrafine spherical nanoparticles having single phase cubic fluorite structure of CeO₂. Raman spectroscopy results have depicted a red shift in F_2g mode with Fe doping which reveals enhancement in the oxygen vacancies. The optical band gap calculated from UV–visible absorption spectra has been found to vary unsystematically with Fe doping which is associated with the creation of impurity level and abundance in oxygen vacancies with Fe doping. The oxygen vacancies have introduced the room temperature ferromagnetism (RTFM) in undoped and Fe doped CeO₂ nanoparticles. The saturation magnetization (M_s) value of pristine CeO₂ nanoparticles has been found to be 0.00083 emu/g which is increased up to 0.0126 emu/g for 7% Fe doped nanoparticles. For cytotoxicity tests, the synthesized nanoparticles induced effects on Neuroblastoma cancer cells & HEK-293 healthy cells have been analyzed via CCK-8 analysis. It has been observed that the prepared undoped and Fe doped CeO₂ nanoparticles have nontoxic nature towards healthy cells while they are extremely toxic towards cancerous cells. Furthermore, the anticancer activity is found to enhance with Fe doping. The selective toxicity and enhancement in anticancer activity with Fe doping has observed to be strongly correlated with reactive oxygen species (ROS) generation.     

Structural,dielectric and photoluminescence properties of co-precipitated Zn-doped SnO2 nanoparticles

Zn-doped SnO₂ nanoparticles were prepared by the chemical co-precipitation route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses of these prepared nanoparticles were carried out for structural and morphological studies. All the samples have been found to have tetragonal rutile structure of the polycrystalline SnO₂ having crystallite size in the range 13–25 nm. TEM micrographs show agglomeration of nanoparticles in all the samples. At a particular temperature, the dielectric constant of all the samples has been found to decrease with increasing frequencies which may be due to rapid polarization processes occurring in SnO₂ nanoparticles. The ac conductivity, σ (ω), has been found to vary with frequency according to the relation σ (ω) ∝ ω^S. The value of S has been found to be temperature dependent, decreasing with increasing frequency which suggests that a hopping process is the most likely conduction mechanism in these nanoparticles. The room temperature photoluminescence (PL) spectra of the undoped and Zn-doped SnO₂ nanoparticles consist of the near band-edge ultraviolet (UV) emission and the defect related visible emissions. The origin of emission peaks in the visible region is attributed to oxygen-related defects that are introduced during growth.     

Defect types and room temperature ferromagnetism in N-doped rutile TiO2single crystals

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device （SQUID）, X-ray photoelectron spectroscopy （XPS）, and positron annihilation analysis （PAS）. Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3＋, arising from titanium vacancies and the replacement of O with N atoms in the futile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism （RTFM）, and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.     

Effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles

We explore the effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles synthesized by the sol-gel method. X-ray diffraction and x-ray photoelectron spectroscopy data show evidence that Cr has been incorporated into the wurtzite ZnO lattice as Cr²⁺ ions substituting for Zn²⁺ ions without any detectable secondary phase in as-synthesized Zn_0.97Cr_0.03O nanopowders. The room temperature magnetization measurements reveal a large enhancement of saturation magnetization M_s as well as an increase of coercivity of H₂-annealed Zn_0.97Cr_0.03O:H samples. It is found that the field-cooled magnetization curves as a function of temperature from 40 to 400 K can be well fitted by a combination of a standard Bloch spin-wave model and Curie–Weiss law. The values of the fitted parameters of the ferromagnetic exchange interaction constant a and the Curie constant C of H₂-annealed Zn_0.97Cr_0.03O:H nanoparticles are almost doubled upon H₂-annealing. Photoluminescence measurements show evidence that the shallow donor defect or/and defect complexes such as hydrogen occupying an oxygen vacancy H_o may play an important role in the origin of H₂-annealing induced enhancement of ferromagnetism in Cr-H codoped ZnO nanoparticles.     

Al掺杂SnO2 材料电子结构和光学性质

采用基于第一性原理的线性缀加平面波方法(FP-LAPW),研究Al掺杂SnO₂材料Sn_1-xAl_xO₂ (x= 0,0.0625,0.125,0.1875,0.25)的电子结 构和光学性质,包括能带结构、电子态密度、介电函数和其他一些光学性质.计算结果表明,掺杂Al之后价带上部分折叠态增加,价带宽度发生收缩,对导带底起作用的Sn 5s态减少,使得带隙增宽,且态密度整体向高能方向发生移动.随着Al掺杂量的增加带隙越来越宽,Al杂质能级在导带部分与Sn 5p态电子相互作用逐渐增强,虚部谱中的第一介电峰的强度随掺杂Al浓度增大而减弱.同时,吸收谱及其他光学谱线与介电函数虚部谱线相对应,各谱线均发生蓝移现象,对应带隙增宽,从理论上指出了光学性质与电子结构之间的内在关系. 关键词： 能带结构 态密度 光学性质 介电函数     

Pressure-induced two-color photoluminescence in MnF(2) at room temperature

A novel two-color photoluminescence (PL) is found in MnF(2) at room temperature under high pressure. Contrary to low-temperature PL, PL at room temperature is unusual in transition-metal concentrated materials like MnF(2), since the deexcitation process at room temperature is fully governed by energy transfer to nonradiative centers. We show that room-temperature PL in MnF(2) originates from two distinct Mn(2+) emissions in the high-pressure cotunnite phase. The electronic structure and the excited-state dynamics are investigated by time-resolved emission and excitation spectroscopy at high pressure.     

A threshold of Vo/Vo to room temperature ferromagnetism of hydrogenated Mn doped ZnO nanoparticles

Hydrogenated Mn doped Zn_1−xMn_xO (x = 0.03, 0.04, 0.08) nanoparticles were prepared by co-precipitation method. With the increase of Mn ions concentration, the magnetization of the hydrogenated Zn_1−xMn_xO increased. Photoluminescence spectra of samples annealed in Ar and H₂ respectively were performed and the visible bands were fitted with Gaussian analysis. It is concluded that the sharp magnetization enhancement could be attributed to the long-rang interaction between bound-magnetic-polarons led by the singly charged oxygen vacancy (Vo⁺).     

Room-temperature ferromagnetism in pure and Mn doped SnO2 powders

We report here observation of ferromagnetism in pure and Mn doped SnO₂ powder with different Mn contents. Magnetic measurements revealed that all samples exhibit room temperature ferromagnetism (RTFM), which is identified as an intrinsic characteristic. The RTFM has been observed in the pure SnO₂ powder, which is believed to be defect induced, with a saturation magnetization of ～0.017 emu/g. The RTFM was enhanced considerably in the Mn doped samples and the magnetic properties strongly depend on doping content. A sample with 1% of Mn is ferromagnetic at room temperature with a saturation magnetization of ～0.98 emu/g, a remanent magnetization of ～27%, and a coercivity of ～270 Oe. The average magnetic moment per Mn atom decreases with increasing Mn content. Our results reveal that the large RTFM observed in Mn doped SnO₂ powder originates from a combination effect of oxygen vacancies and transition metal doping.     

稀释磁性半导体Sn1-xMnxO2的室温铁磁性

采用固相反应法,制备了不同成分的稀释磁性半导体Sn1-xMnxO2(x=0.02,0.04,0.06).利用x射线衍射和傅里叶变换红外光谱法证明了锰均匀地掺杂到二氧化锡中.在室温下研究了掺锰二氧化锡基稀释半导体的磁性,发现它具有明显的铁磁性,同时对磁性的强弱与锰的含量和烧结温度的关系作了研究.     

Defect induced room temperature ferromagnetism in methylammonium lead iodide perovskite

The meteoric rise in the photovoltaic performance of organic-inorganic hybrid perovskite is a conspicuous reflection of its defect tolerance nature. The presence of lattice defect in organo lead halide perovskite can manipulate or even gives rise to some exceptional properties which otherwise would have remained unseen. One of such properties reported in this article is the experimental observation of defect mediated room temperature ferromagnetism in methylammonium lead halide perovskite for the very first time, ably supported by ab-initio calculations. Theoretical analysis predicts that the ferromagnetism principally arises from the iodine vacancies in the orthorhombic and cubic crystal phases but not in the tetragonal phase. The low temperature (100 K) ferromagnetic hysteresis loop was stable even at a high temperature of 380 K, substantiating the fact that the origin of magnetism embedded in its defective nature.     

Spin-polarized room temperature ferromagnetism in co-doped ZnO synthesized by electrodeposition

We have investigated the structural, optical and magnetic properties of Zn_0.90Co_0.10O, synthesized by the method of two electrode electrodeposition. X-ray diffraction measurement confirms the evolution of a single-phase polycrystalline hcp Wurtzite structure. Co-2p core-level XPS confirms that Co is present in mixed 2+ and 3+ states. The Fourier Transform Infrared (FTIR) spectrum findings substantiate the fact that a single-phase Hexagonal Wurtzite ZnO Crystal Structure has evolved. The SEM micrograph of the sample reveals smooth and dispersed morphology consisting of fine particles. The U-V visible NIR and PL spectroscopy measurements substantiate the fact that Co²⁺ has substituted Zn²⁺ in the matrix of ZnO which agrees with XRD findings. The sample shows good optical property and reveals a blue shift. It seems that the material is a potential candidate to be used as UV sensors. Room Temperature Intrinsic Ferromagnetism has been confirmed by VSM measurement.     

Role of donor defects in stabilizing room temperature ferromagnetism in (Mn, Co) co-doped ZnO nanoparticles

We report the effects of co-doping ZnO with Co and Mn in an n-type environment on ferromagnetism (FM). Two sets of samples, Zn(0.95-x)Co(0.04)Mn(x)O (0.000 ≤ x ≤ 0.02) and Zn(0.95-y)Co(y)Mn(0.04)O (0.000 ≤ y ≤ 0.02), were synthesized by the chemical route with oxygen vacancies introduced via annealing in a forming gas (reducing the atmosphere). In addition to the magnetization, the particles were characterized by x-ray diffraction, diffuse reflectance spectroscopy and x-ray absorption near-edge emission spectroscopy. The Co and Mn ions were determined to be in the + 2 state in a tetrahedral symmetry, with no evidence of metallic Co or Mn. We find that while a purely Mn-doped sample exhibits weak FM at room temperature, the general effect of Mn as a co-dopant with Co, in an n-type environment, is to decrease the moment strongly. All of our results can be systematically explained within the context of defect mediated FM in these wide bandgap semiconductors, where the coincidence of the spin-split-impurity (defect) band states and the 3d states leads to the development of a net moment alongside the formation of spin polarons.     

High temperature ferromagnetism with a giant magnetic moment in transparent co-doped SnO(2-delta)

The occurrence of room temperature ferromagnetism is demonstrated in pulsed laser deposited thin films of Sn(1-x)Co(x)O(2-delta) (x<0.3). Interestingly, films of Sn(0.95)Co(0.05)O(2-delta) grown on R-plane sapphire not only exhibit ferromagnetism with a Curie temperature close to 650 K, but also a giant magnetic moment of 7.5+/-0.5 micro(B)/Co, not yet reported in any diluted magnetic semiconductor system. The films are semiconducting and optically highly transparent.     

In situ investigation of ferromagnetism in magnetic nanolayers at room temperature

Ultrathin iron layers on different substrates and a Dy_{1 ? x} Ni _x /Nibilayer have been investigated in situ using the magneto-optical Kerr effect. Ferromagnetic ordering in the Dy_{1 ? x} Ni _x /Nistructure at room temperature has been established. A technique for estimating the thickness of the iron/silicon interface is proposed.     

Field emission and room temperature ferromagnetism properties of triangle-like ZnO nanosheets

Triangle-like ZnO nanosheets have been synthesized via conventional thermal evaporation method at a low temperature of 550 °C using CuO as catalyst. The obtained samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectra. The great influences of Cu catalyst on the morphology of the obtained ZnO nanostructures were investigated. The field emission measurements confirmed that the ZnO nanosheets possessed good performance with a turn-on field of 3.1 V μm⁻¹ and a field enhancement factor of 3250, which have promising application as a competitive cathode material in FE microelectronic devices. Room temperatures ferromagnetism has been observed in the triangle-like ZnO nanosheets, although the products consist of only nonmagnetic elements.     

A possible origin of room temperature ferromagnetism in Indium-Tin oxide thin film: Surface spin polarization and ferromagnetism

Room temperature ferromagnetism in both transition-metals doped and undoped semiconductor thin films and nanostructures challenges our understanding of the magnetism in solids. In this report, we performed the magnetic measurement and Andreev reflection spectroscopy study on undoped Indium-Tin oxide (ITO) thin films and bulk samples. The magnetic measurement results of thin films show that the total magnetization/cm² is thickness independent. Prominent ferromagnetism signal was also discovered in bulk samples. Spin polarized electron transports were probed on ITO thin film/superconductor interface and bulk samples surface/superconductor interface. Based on the magnetic measurement results and spin polarization measurement data, we propose that the ferromagnetism in this material originates from the surface spin polarization and this surface polarization may also explain the room temperature ferromagnetism discovered in other undoped oxide semiconductor thin films and nanostructures.