Zhengang Guo

Structural and room-temperature ferromagnetic properties of Fe-doped CuO nanocrystals

Fe-doped CuO (Cu1−xFexO) nanocrystals (NCs) (x=0, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3) are prepared by using the urea nitrate combustion method. X-ray diffraction (XRD) analysis confirmed the monoclinic structure of CuO. Single-phase structure is obtained for the 0%–20% Fe-doped CuO, whereas for the 25% and 30% Fe-doped CuO material, secondary phase, α-Fe2O3, is presented. Rietveld refinements of XRD data revealed that with an increase in Fe doping level, there is a monotonic increase in cation vacancies in the Fe-doped samples. X-ray photoelectron spectroscopy measurements on the Cu0.98Fe0.02O sample revealed that the Cu2+ sites are partly substituted by Fe3+ ions. The microstructure is investigated by high-resolution transmission electron microscopy. The magnetic hysteresis loops and the temperature dependence of magnetization of the samples indicated that the samples are mictomagnetic of ferromagnetic domains originated from ferromagnetic coupling between the doping Fe ions in Cu1−xFexO NCs rando...

Ferromagnetism analysis of Mn-doped CuO thin films

Mn (6.6–29.8%)-doped CuO thin film fabricated on a thermally oxidized silicon substrate by radio-frequency magnetron sputtering has been reported. The films were structurally characterized using x-ray diffraction with Rietveld refinement. The analysis indicates that Mn uniformly substituted at the Cu position in the CuO lattice. 5% cation vacancies were detected at the Cu sites and are supposed to be responsible for the p-type electrical conduction of Cu1−xMnxO films. No evidence for large scale Mn aggregation was found in the composition range analyzed. The origin of ferromagnetism was analyzed in the context of competition among several interactions among Mn and Cu ions. A chain model was developed to simulate the ferromagnetic behavior with the random Mn distribution in the samples. The consistency between simulation and experiment strongly indicates that the ferromagnetism mainly arises from the super-exchange interactions of Mn–O–Cu–O–Mn coupling in the [] chain and Mn–O–Mn coupling contributes to the antiferromagnetism.

STRUCTURAL, MAGNETIC AND DIELECTRIC PROPERTIES OF Fe-DOPED BaTiO3 SOLIDS

The structural, ferroelectric and magnetic properties of bulk perovskite Fe-doped BaTiO3 (BFTO) prepared by standard solid-state reaction have been investigated. X-ray diffraction (XRD) identifies the tetragonal structure of BFTO samples. Rietveld refinements of XRD data indicates that the doping ions led to ab-plane expansion and out-of-ab-plane shrinkage of the BFTO phases. X-ray photoelectron spectroscopy (XPS) measurements for the prepared samples reveals that Fe3+ and Fe4+ ions replaces Ti4+ ions in the crystal lattice to form single-phase BFTO solids. The results of the temperature-dependent dielectric properties and magnetic hysteresis loops for the BFTO solids show simultaneously the ferroelectric order and ferromagnetic order at room temperature. The doping of magnetic element Fe brings about ferromagnetic order for the samples, and the measured magnetic moment for each Fe atom increases from 0.70 μB to 1.55 μB in BFTO samples. The origin of ferromagnetism of the BFTO samples should be attributed to the double exchange interactions of Fe3+–O2–Fe4+ ions.

Controlled synthesis, phase formation, growth mechanism, and magnetic properties of 3-D CoNi alloy microstructures composed of nanorods

3-D flower like CoNi alloys nanostructures composed of nanorods have been synthesized by template free hydrothermal method at relatively low temperature (120 °C). The detailed characterizations confirm the formation of good crystalline fcc CoNi alloy, average crystallite size of 18.8 ± 1.0 nm, lattice parameter of 3.531 ± 0.01 A, and the nearly equiatomic composition (Co50Ni50). Highly uniform flower like nano structures are built up with nanorod of diameter about 100 nm and length in range of 200–400 nm. The nanorods (building blocks of flower) have single crystalline nature with [111] preferred growth direction. The concentration of NaOH plays a vital role in formation of alloys and high concentration promotes the formation of CoNi alloy at low temperature. The concentration of NaOH also affects the morphology remarkably by changing the growth/reaction rate of CoNi nanostructures and results in hollow spheres to nanoplate flower of CoNi alloys. Based on the evolution of the morphology of the products, a step wise growth mechanism is rationally proposed for flower like nanostructures by considering the effects of kinetic parameters on growth. Magnetic measurements show Co50Ni50 flower like nanostructure have high saturation magnetization, coercivity, remanent magnetization, and high effective anisotropy constant of value 101.3 emu g−1, 210.5 Oe, 16.2 emu g−1, and 4.457 × 104 J m−3 respectively. The enhancements of coercivity and effective anisotropy constant are attributed to nanoscale effects such as shape/surface anisotropy.

Fabrication and magnetic properties of ferromagnetic Co50Fe50 nanorings

In this paper, ferromagnetic Co50Fe50 nanorings were fabricated by template-assisted sputtering deposition. The obtained Co50Fe50 nanorings have a good dimensional uniformity, with outer diameter of 360 nm, width of 50 nm and thickness of 40 nm. The magnetic properties of Co50Fe50 nanorings were investigated by micromagnetic simulations and vibrating sample magnetometer. We observed two parallel magnetic switching processes in the micromagnetic simulations of nanorings, the vortex formation process and onion rotation process, respectively. Quantitative analysis on the basis of experimental results indicates that 43.7% of the Co50Fe50 nanorings undergo the vortex formation process and others undergo the onion rotation process.