Room temperature ferromagnetism in chemically synthesized ZnO rods

We report structural and magnetic properties of pure ZnO rods using x-ray diffraction (XRD), magnetization hysteresis (M−H) loop and near edge x-ray fine structure spectroscopy (NEXAFS) study at O K edge. Sample of ZnO was prepared by co-precipitation method. XRD and selective area electron diffraction measurements infer that ZnO rods exhibit a single phase polycrystalline nature with wurtzite lattice. Field emission transmission electron microscopy, field emission scanning electron microscopy micrographs infers that ZnO have rod type microstructures with dimension 200 nm in diameter and 550 nm in length. M-H loop studies performed at room temperature display room temperature ferromagnetism in ZnO rods. NEXAFS study reflects absence of the oxygen vacancies in pure ZnO rods.     

Room temperature ferromagnetism in Tb-doped ZnO dilute magnetic semiconducting nanoparticles

Pure and Tb-doped ZnO nanoparticles have been synthesized by chemical co-precipitation method. The transmission electron microscopy study reveals the spherical morphology of synthesized nanoparticles with average particle size 14–18 nm. The effect of Tb-doping on structural, optical and magnetic properties has been studied. X-ray diffraction shows that pure and Tb-ZnO nanoparticles exhibit wurtzite structure having hexagonal phase with primitive unit cell. It further reveals that there is no effect of Tb-doping on the X-ray diffraction pattern up to 2 % doping, however, higher doping concentration result in accumulation of Tb on ZnO surface. Photoluminescence spectra reveal that the doping Tb in ZnO changes crystallographic structure generating non-radiative oxygen vacancies. Three emission peaks located around 423, 485 and 515 nm has been observed. Pure ZnO nanoparticles show diamagnetic character, however, Tb-doped ZnO nanoparticles exhibit room temperature ferromagnetism. The correlation between defects generated upon Tb-doping to the observed ferromagnetism, in the synthesized nanoparticles, has been reported.     

Room temperature ferromagnetism in solvothermally synthesized pure CdSe and CdSe:Ni nanorods

We report here room temperature ferromagnetism in CdSe and Ni-doped CdSe nanorods. Pure and 3% Ni-doped CdSe nanorods are synthesized by using low temperature solvothermal process by using ethylenediamine as solvent. X-ray diffractogram depicts the wurtzite (hexagonal) structure of the CdSe nanorods. From Transmission Electron Microscopy analysis, it is found that the average diameter of the CdSe nanorods is about 4–5 nm having length of about 50 nm. Magnetic studies are made by the analysis of M–H curves, obtained by using Superconducting Quantum Interference Device. The room temperature ferromagnetic behaviour has been shown by both pure CdSe as well as Ni-doped CdSe nanorods.     

Room temperature ferromagnetism in Ni doped In2O3 nanoparticles

In the present work, Ni doped In₂O₃ nanoparticles were prepared using simple co-precipitation method. From the x-ray diffraction analysis it is observed that all samples exhibit single phase polycrystalline nature. All the diffraction lines correspond to the bixbyite type cubic structure. A UV visible analysis reveals that optical band gap decreases from 4.63 to 3.84 eV with Ni doping. DC magnetization measurements reveal that Ni doped In₂O₃ nanoparticles exhibit room temperature ferromagnetism.     

Room temperature ferromagnetism in Co-incorporated TiO2 thin films

Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.     

Room temperature ferromagnetism in Zn0.99La0.01O and pure ZnO nanoparticles

Room temperature ferromagnetism (RTFM) was observed in both La-doped and pure ZnO nanoparticles synthesized by the sol–gel method. RTFM is intrinsic according to the results of X-ray diffraction and X-ray photoelectron spectroscopy. The saturation magnetization (M_S), the remnant magnetization at zero field and coercive field are 5 × 10⁻³, 7 × 10⁻⁴ emu g⁻¹, 100 Oe for Zn_0.99La_0.01O nanoparticles and 1.5 × 10⁻⁴, 1 × 10⁻⁵ emu g⁻¹, 50 Oe for pure ZnO nanoparticles, respectively. The magnetization is enhanced greatly by doping of La. Furthermore, the M_S of Zn_0.99La_0.01O nanoparticles decreases from 0.005 to 0.001 emu g⁻¹ as the annealing temperature increases from 500 to 700 °C. The doping of La introduces more oxygen vacancies into ZnO. The decrease of annealing temperature also produces more oxygen vacancies in La-doped ZnO. These results indicate that the origin of the RTFM is related to oxygen vacancies.     

Room temperature ferromagnetism in laser ablated Zn ferrite thin films

Nanocrystalline ZnFe₂O₄ was synthesized using sol–gel method. The room temperature ferromagnetic behavior was observed in ZnFe₂O₄ thin films fabricated by pulsed laser deposition (PLD) technique. The ZnFe₂O₄ nanoparticles and target material used for the fabrication of thin films was observed to have paramagnetic behavior at room temperature. The possible ferromagnetic behavior observed in ZnFe₂O₄ thin films has been explained in terms of random distribution of Zn²⁺ and Fe³⁺ ions at tetrahedral (A) and octahedral [B] sites. The blocking temperature T_B was observed in the case of both nanoparticles and thin films.     

Room temperature ferromagnetism in triple perovskite Sr3CrFeMoO9

Triple perovskite Sr₃CrFeMoO₉ was designed and prepared in reducing atmosphere. The ceramics are single phase with homogeneous, porous-like microstructure. The valences of the interior Cr, Fe, and Mo cations are +3, +2/+3, 0/+6, whereas that of the surface cations are +3, +3, and +6, respectively. The ceramics show well-saturated magnetization-magnetic field hysteresis loop, the saturation magnetizations are 1.0 and 0.6 μ_B per formula unit at 10 K and room temperature, respectively. The ferromagnetic Curie temperature is determined to be 385 K. Furthermore, semiconductor behavior in the measuring temperature range (10–300 K) and large negative magnetoresistance of ?30.7 % at 10 K are observed. Our results may stimulate further works on room temperature ferromagnetism in triple perovskite.     

Room temperature ferromagnetism and hopping transport in amorphous CrN thin films

Magnetic and electronic properties of stoichiometric amorphous CrN thin films grown on MgO (001) substrates by radio-frequency nitrogen-plasma-assisted molecular beam epitaxy have been investigated. The magnetic property of the amorphous CrN thin films shows a ferromagnetic behavior even at room temperature, and can be interpreted by the percolation theory of magnetic polaron where we consider Cr³⁺ defects as magnetic impurities which lead to the formation of bound magnetic polarons. The obtained results of electrical conductivity are explained by the variable-range-hopping theory of the Mott and Davis model.     

溶胶-凝胶法制备Cu/ZnO的室温铁磁性

为研究稀磁性半导体的室温铁磁性来源,采用溶胶-凝胶法制备了Cu掺杂ZnO半导体粉末。X射线衍射光谱显示Cu在ZnO中的固溶度小于0.08 (摩尔比);透射电子显微镜分析显示颗粒尺寸较为均匀,呈单结晶态;振动样品磁强计测试表明,Cu/ZnO具有室温铁磁性。由于Cu本身不具有任何磁性,样品的铁磁性来源为氧化锌晶格中的缺陷与Cu2+离子之间的交换作用。     

Room temperature magnetism in Ni-doped CdSe nanoparticles

Room temperature ferro-magnetism in Ni-doped CdSe nanoparticles (NPs) synthesized by a wet chemical precipitation method is reported. Transmission electron microscopy shows that the average particle size of Ni-doped CdSe NPs is about 8 nm. X-ray diffraction shows the zinc blende (cubic) structure of Cd_1-x Ni _x Se NPs. Superconducting quantum interference device was utilized to study the magnetic behavior of NPs. Magnetic studies revealed that pure CdSe NPs exhibit diamagnetic behavior at 300 K, whereas 5% Ni doped CdSe NPs shows the mixture of paramagnetic and ferromagnetic behavior.     

Signature of room temperature ferromagnetism in Mn doped CeO2 nanoparticles

We report structural and magnetic properties of Mn doped CeO₂ nanoparticles using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM) and dc magnetization measurements. XRD results infer that all the samples have single phase nature and lattice parameters decrease with Mn doping. The particle size calculated using XRD and TEM analysis was found to decrease with Mn doping. Field cooled magnetization measurement shows that the transition temperature is above room temperature. Magnetic hysteresis loop studies indicate that undoped and Mn doped CeO₂ nanoparticles show weak ferromagnetic behavior at room temperature.     

Room temperature synthesis of colloidal platinum nanoparticles

Efficient preparation of stable dispersions of platinum nanoparticles from platinous chloride (K₂PtCl₄) was achieved by simultaneous addition of capping polymer material. The size of platinum nanoparticles was controlled by changing the ratio of concentration of capping polymer material to the concentration of platinum cation used. The morphology of colloidal particles were studied by means of UV-visible spectrophotometry and transmission electron microscopy (TEM). Particle size increased with low reagent concentration. The change in absorption spectra with the particle size was observed, i.e. blue shift attributed to decrease in particle size Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

PZT ceramics obtained from mechanochemically synthesized powders

PZT ceramics were obtained from the mechanochemically synthesized powders. Milling and sintering conditions were optimized based on results of density measurements, as well as on microstructural and electrical characterization. As a result, highly dense and homogeneous ceramics were obtained. Excellent microstructural properties resulted in good electrical properties. Samples showed values of dielectric constants reaching 12 800 at the Curie temperature, as well as low dielectric loss under the optimal processing conditions. High values of remanent polarization, reaching 60 C cm^–2, indicate high internal polarizability.     

Room temperature ferromagnetism in Co doped ZnO within an optimal doping level of 5%

We report on the structural, micro-structural and magnetic properties of Zn_1?xCo_xO (0 ≤ x ≤ 0.1) system. Electron probe micro-structural analysis on 5% Co doped ZnO indicates the presence of segregated cobalt oxide which is also confirmed from the Co 2p core level X-ray photoelectron spectrum. The presence of oxygen defects in lower percentage of Co doped ZnO (≤5%) enhances the carrier mediated exchange interaction and thereby enhancing the room-temperature ferromagnetic behaviour. Higher doping percentage of cobalt (>5%) creates weak link between the grains and suppresses the carrier mediated exchange interaction. This is the reason why room temperature ferromagnetism is not observed in 7% and 10% Co doped ZnO.     

Comparative study of room temperature ferromagnetism in undoped and Ni-doped TiO2 nanowires synthesized by solvothermal method

We report a comparative study of room temperature ferromagnetism (RTFM) in undoped and Ni-doped TiO₂ nanowires synthesized by solvothermal method. Both undoped and Ni-doped TiO₂ nanowire samples showed the RTFM with coercive field of ~125 Oe due to intrinsic effect. Interestingly, compared to the doped TiO₂ nanowires, the undoped nanowires exhibited the higher saturation magnetization value, indicating surface defects such as Ti³⁺ and oxygen vacancy play more important role in realizing RTFM than Ni doping. The origin of RTFM in the undoped nanowires can be attributed to the ferromagnetic coupling between Ti³⁺ ions via F⁺ center resulting from oxygen vacancy on the nanowire surface. Furthermore, saturation magnetization value of the doped nanowires is increased with increasing the doping concentration due to the enhanced ferromagnetic coupling between Ni²⁺ ions via F⁺ center.     

Room temperature synthesis of crystalline alpha-Fe2O3 nanoparticles

A room temperature process for the production of crystalline hematite Fe2O3 nanoparticles with an indirect band gap of 2 eV and size range from 15 to 35 nm is presented. The material to have an optical band gap of 2 eV as determined by the Tauc relationship which makes it suitable for visible light photocatalysis. The XRD pattern of the material shows no secondary phases to be present for the low temperature processed material.     

Room temperature self-organized gold nanoparticles materials for embedded electronic devices

In this study, we synthesize two different sizes of gold nanoparticles (NPs) with uniform size distribution. A novel technique of fabricating gold NPs embedded capacitor devices utilizing chemical self-assembled gold NPs has been developed. Room temperature process and uniform size distribution of gold NPs device are built and characterized. These electronic devices have lower leakage current, no metal diffusion problem, larger memory window, better charge retention time and following Fowler–Nordheim tunneling model. This method enables the possibility of future memory applications to fabricate devices with this simple and versatile technique based on the NPs assembly.