Unraveling the effect of Gd doping on the structural,optical, and magnetic properties of ZnO based diluted magnetic semiconductor nanorods

The structural, magnetic, and optical properties of the pristine and Gd-doped ZnO nanorods (NRs), prepared by facile thermal decomposition, have been studied using a combination of experimental and density functional theory (DFT) with Hubbard U correction approaches. The XRD patterns demonstrate the single-phase wurtzite structure of the pristine and doped ZnO. The rod-like shape of the nanoparticles has been examined by FESEM and TEM techniques. Elemental compositions of the pure and doped samples were identified by EDX measurement. Due to the Burstein–Moss shift, the optical band gaps of the doped samples have been widened compared to pristine ZnO. The PL spectra show the presence of complex defects. Room temperature magnetic properties have been measured using VSM and revealed the coexistence of paramagnetic and weak ferromagnetic ordering in Gd³⁺ doped ZnO-NRs. The magnetic moment was increased upon addition of more Gd ions into the ZnO host lattice. The DFT+U calculations confirm that the presence of vacancy-complexes has a significant effect on the structural, electronic, and magnetic properties of a pristine ZnO system.

Gd doped ZnO nanorods.     

Fiber optic magnetic field sensor using Co doped ZnO nanorods as cladding

A fiber optic magnetic field sensor is proposed and experimentally demonstrated. Pristine and Co doped ZnO nanorods of different Co concentrations (5, 10, 15 and 20 at%) were synthesized using a hydrothermal method. The synthesized nanorods were subjected to various characterization methods like X-ray diffraction (XRD), optical absorption, scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometry and X-ray photoelectron spectroscopy (XPS). XRD and XPS analysis confirms that the Co ions were successfully incorporated into the Zn site of the wurtzite ZnO lattice without altering the structure. The pristine and Co doped ZnO nanorods showed remarkable changes in the M–H loop where the diamagnetic behavior of ZnO changes to paramagnetic when doped with Co. The sensor structure is composed of cladding modified fiber coated with Co doped ZnO nanorods as a sensing material. The modified cladding is proportionally sensitive to the ambient magnetic field because of the magneto-optic effect. Experimental results revealed that the sensor has an operating magnetic field range from 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods. The proposed magnetic field sensor would be attractive due to its low cost fabrication, simplicity of the sensor head preparation, high sensitivity and reproducibility.

A fiber optic magnetic field sensor based on Co doped ZnO nanorods is proposed and demonstrated. The sensor has an operating magnetic field range of 17 mT to 180 mT and shows a maximum sensitivity of ∼18% for 15 at% Co doped ZnO nanorods.     

Structural and magnetic study of undoped and cobalt doped TiO2 nanoparticles

The present study investigates the influence of cobalt doping on the structural and magnetic properties of TiO₂ nanoparticles prepared by a simple wet chemical method. The single phase anatase structure of Co-doped TiO₂ nanoparticles was confirmed by X-ray powder diffraction. A morphological study using scanning electron microscopy and transmission electron microscopy indicates the formation of TiO₂ nanoparticles of sizes 6–10 nm. The high resolution TEM image shows clear lattice fringes indicating the highly crystalline nature of the nanoparticles which was further analysed by selected area electron diffraction pattern which indicates a polycrystalline nature of anatase TiO₂. The shifting and broadening of the most intense E_g (1) mode in micro-Raman study of Co-doped TiO₂ nanoparticles and XPS spectra indicate the incorporation of Co in TiO₂. Magnetic measurement shows ferromagnetic behavior at room temperature in undoped TiO₂ which has originated due to the presence of oxygen vacancies which are intrinsic in nature. But the M–H curve of Co-doped TiO₂ shows the coexistence of ferromagnetic and paramagnetic phases with enhanced magnetization. The enhancement in magnetization has arisen due to Co doping and the paramagnetism may be due to the presence of some undetected clusters of oxides of cobalt.

The present study investigates the influence of cobalt doping on the structural and magnetic properties of TiO₂ nanoparticles prepared by a simple wet chemical method.     

5-氟尿嘧啶磁性纳米粒的制备及性能

背景:磁性载药微粒在外加磁场作用下,能实现定向治疗作用,减少全身毒副作用,同时作为缓释载体,能减少药物的频繁给药,达到有效治疗目的.目的:制备5-氟尿嘧啶的磁性纳米粒,评价微球性能.方法:以海藻酸钠和壳聚糖作为壁材,5-氟尿嘧啶为模型药物,Span80为乳化剂,液体石蜡为分散介质,乳化-复凝聚法制备磁性纳米粒.并从外观、稳定性、磁响应性、结构、溶胀实验及体外释放实验等多方面考察纳米粒性能.结果与结论:所制5-氟尿嘧啶的磁性纳米粒形态良好,均匀圆整,分散性较好,粒径在100～300 nm,具有较好稳定性和磁响应性.考察Fe3O4用量的影响,发现随着Fe3O4用量的增加,磁响应性增强,但载药量下降.红外谱图说明微粒中包裹磁性物质Fe3O4,及5-氟尿嘧啶与壁材之间产生相互作用.将5-氟尿嘧啶磁性纳米粒分别浸渍在蒸馏水,0.9%NaCl溶液和磷酸盐缓冲液(pH=7.4)中,结果蒸馏水吸水速度最快且溶胀率最大,磷酸盐缓冲液(pH=7.4)吸水程度最小且溶胀率最小.微粒的缓释性能良好,50 h内释放的药物占总含药量的53.20%.     

Experimental and ab initio studies on the structural,magnetic, photocatalytic,and antibacterial properties of Cu-doped ZnO nanoparticles

Copper-doped ZnO nanoparticles with a dopant concentration varying from 1–7 mol% were synthesized and their structural, magnetic, and photocatalytic properties were studied using XRD, TEM, SQUID magnetometry, EPR, UV-vis spectroscopy, and first-principles methods within the framework of density functional theory (DFT). Structural analysis indicated highly crystalline Cu-doped ZnO nanoparticles with a hexagonal wurtzite structure, irrespective of the dopant concentration. EDX and EPR studies indicated the incorporation of doped Cu²⁺ ions in the host ZnO lattice. The photocatalytic activities of the Cu-doped ZnO nanoparticles investigated through the degradation of methylene blue demonstrated an enhancement in photocatalytic activity as the degradation rate changed from 9.89 × 10⁻⁴ M min⁻¹ to 4.98 × 10⁻² M min⁻¹. By the first-principles method, our results indicated that the Cu(3d) orbital was strongly hybridized with the O(2p) state below the valence band maximum (VBM) due to covalent bonding, and the ground states of the Cu-doped ZnO is favorable for the ferromagnetic state by the asymmetry of majority and minority states due to the presence of unpaired electron.

Magnetic, photocatalytic and antibacterial performance of ZnO NPs were enhanced as doped with Cu.     

Size-dependent magnetic and magnetothermal properties of gadolinium silicide nanoparticles

Gadolinium silicide (Gd₅Si₄) nanoparticles are an interesting class of materials due to their high magnetization, low Curie temperature, low toxicity in biological environments and their multifunctional properties. We report the magnetic and magnetothermal properties of gadolinium silicide (Gd₅Si₄) nanoparticles prepared by surfactant-assisted ball milling of arc melted bulk ingots of the compound. Using different milling times and speeds, a wide range of crystallite sizes (13–43 nm) could be produced and a reduction in Curie temperature (T_C) from 340 K to 317 K was achieved, making these nanoparticles suitable for self-controlled magnetic hyperthermia applications. The magnetothermal effect was measured in applied AC magnetic fields of amplitude 164–239 Oe and frequencies 163–519 kHz. All particles showed magnetic heating with a strong dependence of the specific absorption rate (SAR) on the average crystallite size. The highest SAR of 3.7 W g⁻¹ was measured for 43 nm sized nanoparticles of Gd₅Si₄. The high SAR and low T_C, (within the therapeutic range for magnetothermal therapy) makes the Gd₅Si₄ behave like self-regulating heat switches that would be suitable for self-controlled magnetic hyperthermia applications after biocompatibility and cytotoxicity tests.

Gadolinium silicide (Gd₅Si₄) nanoparticles prepared by surfactant-assisted ball milling exhibit a size-dependent reduction in magnetic ordering temperature and a high magnetothermal effect making them suitable for magnetic hyperthermia applications.     

High responsivity and 1/f noise of an ultraviolet photodetector based on Ni doped ZnO nanoparticles

This study involves the novel fabrication of a high responsivity, fast response, and low-cost (UV) photodetector (PD) based on ZnO/Ni nanoparticles deposited on a glass substrate. The ZnO/Ni nanoparticles were synthesized using a polyol process. The structure and the morphology of the samples were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Optical properties were measured using UV-visible, diffuse reflectance and photoluminescence (PL) spectroscopy. The photodetector exhibited high photoresponse characteristics under 375 nm laser excitation. Our device shows a high responsivity (121 A W⁻¹) with rise time (about 5.52 s) and fall time (about 12 s) at a bias voltage of 1 V. The device exhibits excellent reproducibility and stability characteristics with time. The noise spectra obtained from the UV photodetector were caused by the 1/f noise. The noise-equivalent power (NEP) is 1.08 × 10⁻⁹ W. Thus, the polyol process can be a useful and effective method for improving the performance of ZnO/Ni UV photodetectors.

This study involves the novel fabrication of a high responsivity, fast response, and low-cost (UV) photodetector (PD) based on ZnO/Ni nanoparticles deposited on a glass substrate.     

Synthesis of ZnO doped high valence S element and study of photogenerated charges properties

Nonmetal doping is an efficient way to increase the photoresponse range of ZnO. However, the mechanism for improving the light response range of ZnO with nonmetal doping is not clear. Herein, ZnO doped with S was successfully prepared by ion exchange and calcination methods, which resulted in the uniform distribution of sulfur ions in ZnO. The S element doped was mainly S⁴⁺ and S⁶⁺, which was identified by XPS. We studied the influence of S on the photogenerated charge characteristics of ZnO with SPS. Results indicated that the uniform distribution of S dopants elevated the valence band maximum by mixing S 3p with the upper valence band states of ZnO. The valence band maxima of S–ZnO was 0.37 eV higher than that of ZnO. This result was the main reason for the improvement in the light response. We also studied the photocatalytic activity of Ag/S–ZnO. Ag/S–ZnO with 10 wt% Ag loading showed the highest photocatalytic degradation rate for MO. In this paper, a potential photocatalytic mechanism has been proposed.

The uniform distribution of S dopants elevated the valence band maximum by mixing S 3p with the upper valence band states of ZnO. The valence band maxima of S–ZnO was 0.37 eV higher than that of ZnO.     

Room temperature dilute magnetic semiconductor response in (Gd,Co) co-doped ZnO for efficient spintronics applications

The co-precipitation approach was utilized to experimentally synthesize ZnO, Zn_0.96Gd_0.04O and Zn_0.96−xGd_0.04Co_xO (Co = 0, 0.01, 0.03, 0.04) diluted magnetic semiconductor nanotubes. The influence of gadolinium and cobalt doping on the microstructure, morphology, and optical characteristics of ZnO was investigated, and the Gd doping and Co co-doping of the host ZnO was verified by XRD and EDX. The structural investigation revealed that the addition of gadolinium and cobalt to ZnO reduced crystallinity while maintaining the preferred orientation. The SEM study uncovered that the gadolinium and cobalt dopants did not affect the morphology of the produced nanotubes, which is further confirmed through TEM. In the UV-vis spectra, no defect-related absorption peaks were found. By raising the co-doping content, the crystalline phase of the doped samples was enhanced. It was discovered that the dielectric response and the a.c. electrical conductivity display a significant dependent relationship. With the decreasing frequency and increasing Co co-dopant concentration, the ε_r and ε′′ values decreased. It was also discovered that the ε_r, ε′′, and a.c. electrical conductivity increased when doping was present. Above room temperature, co-doped ZnO nanotubes exhibited ferromagnetic properties. The ferromagnetic behaviour increased as Gd (0.03) doping increased. Increasing the Co content decreased the ferromagnetic behaviour. It was observed that Zn_0.96−xGd_0.04Co_xO (x = 0.03) nanotubes exhibit superior electrical conductivity, magnetic and dielectric characteristics compared to pure ZnO. This high ferromagnetism is typically a result of a magnetic semiconductor that has been diluted. In addition, these nanoparticles are utilized to design spintronic-based applications in the form of thin-films.

The structure parameters of the synthesize ZnO, Zn_0.96Gd_0.04O and Zn_0.96−xGd_0.04Co_xO (Co = 0, 0.01, 0.03, 0.04) diluted magnetic semiconductor nanotubes.     

Tuning of spinel magnesium ferrite nanoparticles with enhanced magnetic properties

Monodispersed magnesium ferrite nanoparticles with enhanced magnetic properties were successfully fabricated by a simple solvothermal method without employing any templates, complex apparatus or techniques. The structure, morphology, composition, and magnetic properties of the products were tuned and characterized by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy and vibrating sample magnetometry. The results show that the reaction time and temperature have an important influence on the morphology, composition, structure and particle size of the synthesized MgFe₂O₄ nanoparticles. Not only the size, size distribution, crystallization, but also the atomic ratio of Mg : Fe has a decisive effect on their magnetic properties. The MgFe₂O₄ magnetic nanoparticles synthesized at 180 °C for 12 hours have excellent dispersion, narrow size distribution, good crystallinity and a Mg : Fe atomic ratio of approximately 1 : 4.53 and an average particle size of 114.3 nm, thus the highest saturation magnetization of 67.35 emu g⁻¹. It provides a reliable synthesis method for the better application of spinel structure magnesium ferrite nanoparticles in the future.

Monodispersed magnesium ferrite nanoparticles with enhanced magnetic properties were successfully fabricated by a simple solvothermal method without employing any templates, complex apparatus or techniques.     

Characterization of optical properties of ZnO nanoparticles for quantitative imaging of transdermal transport

Widespread applications of ZnO nanoparticles (NP) in sun-blocking cosmetic products have raised safety concerns related to their potential transdermal penetration and resultant cytotoxicity. Nonlinear optical microscopy provides means for high-contrast imaging of ZnO NPs lending in vitro and in vivo assessment of the nanoparticle uptake in skin, provided their nonlinear optical properties are characterized. We report on this characterization using ZnO NP commercial product, Zinclear, mean-sized 21 nm. Two-photon action cross-section of this bandgap material (E(bg) = 3.37 eV, λ(bg) = 370 nm) measured by two techniques yielded consistent results of [Formula: see text] = 6.2 ± 0.8 μGM at 795 nm, and 32 ± 6 μGM at 770 nm per unit ZnO crystal cell, with the quantum efficiency of [Formula: see text] = (0.9 ± 0.2) %. In order to demonstrate the quantitative imaging, nonlinear optical microscopy images of the excised human skin topically treated with Zinclear were acquired and processed using [Formula: see text] and [Formula: see text]values yielding nanoparticle concentration map in skin. Accumulations of Zinclear ZnO nanoparticles were detected only on the skin surface and in skin folds reaching concentrations of 800 NPs per μm(3).     

Photocatalytic properties of Cu-containing ZnO nanoparticles and their antifungal activity against agriculture-pathogenic fungus

In this work, nanoparticles (NPs) of ZnO, ZnO with Cu incorporated at 2 and 30 wt%, and CuO were prepared by the hydrothermal method. X-ray diffraction pattern (DRX) analysis showed that ZnO with high Cu incorporation (30 wt%) generates the formation of a composite oxide (ZnO/CuO), while X-ray photoelectron spectroscopy (XPS) of the Cu (2 wt%) sample indicated that Cu is incorporated as a dopant (ZnO/Cu_2%). The samples with Cu incorporated had enhanced visible light absorption. Methyl orange (MO) dye was used to perform photocatalytic tests under UV radiation. The antifungal activity of the NPs was tested against four agricultural phytopathogenic fungi: Neofusicoccum arbuti, Alternaria alternata, Fusarium solani, and Colletotrichum gloeosporioides. The ZnO/Cu_2% nanoparticles showed adequate photocatalytic and high antifungal activity in comparison to pure oxides and the composite sample.

In this work, nanoparticles (NPs) of ZnO, ZnO with Cu incorporated at 2 and 30 wt%, and CuO were prepared by the hydrothermal method.     

Probing the properties of lattice vibrations and surface electronic states in magnetic semiconductor CrPS4

Searching for multifunctional materials with magnetism and semiconductivity is one of the goals of research into two-dimensional (2D) systems. Herein, we report a chemical vapor transport method to successfully synthesize a layered magnetic semiconductor, CrPS₄. Under parallel and perpendicular polarization configurations, the anisotropic optical response of the (001) surface was investigated by polarized Raman spectroscopy; the Raman peak intensity was recorded with the crystal rotated from 0° to 360°, taking the symmetry of the Raman tensor into account; the A or B vibrational mode of different Raman peaks can be clearly distinguished. Moreover, the electronic state of the (001) single-crystal surface was investigated by ultraviolet photoelectron spectroscopy (UPS), which reveals the valence band position and work function of the (001) surface.

Searching for multifunctional materials with magnetism and semiconductivity is one of the goals of research into two-dimensional (2D) systems.     

Structural,magnetic and hyperthermia properties and their correlation in cobalt-doped magnetite nanoparticles

Cobalt doped magnetite nanoparticles (Co_xFe_3−xO₄ NPs) are investigated extensively because of their potential hyperthermia application. However, the complex interrelation among chemical compositions and particle size means their correlation with the magnetic and heating properties is not trivial to predict. Here, we prepared Co_xFe_3−xO₄ NPs (0 ≤ x ≤ 1) to investigate the effects of cobalt content and particle size on their magnetic and heating properties. A detailed analysis of the structural features indicated the similarity between the crystallite and particle sizes as well as their non-monotonic change with the increase of Co content. Magnetic measurements for the Co_xFe_3−xO₄ NPs (0 ≤ x ≤ 1) showed that the blocking temperature, the saturation magnetization, the coercivity, and the anisotropy constant followed a similar trend with a maximum at x = 0.7. Moreover, ⁵⁷Fe Mössbauer spectroscopy adequately explained the magnetic behaviour, the anisotropy constant, and saturation magnetization of low Co content samples. Finally, our study shows that the relaxation loss is a primary contributor to the SAR in Co_xFe_3−xO₄ NPs with low Co contents as well as their potential application in magnetic hyperthermia.

The interrelation among chemical compositions, structure, and heating properties of cobalt doped magnetite nanoparticles (Co_xFe_3−xO₄ NPs) for their potential hyperthermia application.     

The application of ZnO luminescent nanoparticles in labeling mice

Photoluminescent ZnO@polymer core–shell nanoparticles were used in mouse imaging through intradermal injections and intravenous injections, and the results proved that such ZnO fluorescence probes are nontoxic to live mice and have great potential in in vivo applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Resistive switching effect and magnetic properties of iron oxide nanoparticles embedded-polyvinyl alcohol film

In this study, the memory device of iron oxide (IO) nanoparticles (NPs) embedded in polyvinyl alcohol (PVA) demonstrates the bipolar resistive switching characteristics under an external electric field. The phase and magnetic properties of iron oxide nanoparticles change corresponding to its resistive states. At the high resistance state (HRS) of device, iron oxide nanoparticles are primarily in Fe₂O₃ phase and the ferromagnetism behavior is observed. In contrast, the iron oxide nanoparticles clustered by the bridging oxygen vacancies lead to mainly Fe₃O₄ phase and no hysteresis magnetic curve is observed at the low resistance state (LRS) of device. The results reveal that oxygen vacancies/ions in nanoparticles notably influence the resistance and magnetic behavior of nanocomposite thin films. Our study indicated that the magnetic NPs is high potential of multi-dimensional storage fields.

Bipolar resistive switching behavior of iron oxide nanoparticles embedded into polyvinyl alcohol matrix.     

SiO2/Ni核壳结构纳米粒子的制备及其磁性

背景:包覆层的存在能够阻止纳米粒子氧化、晶体长大、腐蚀和团聚,并赋予特殊的性能.目的:制备SiO2/Ni核壳结构纳米粒子,并评估复合粉体的磁性能.设计、时间及地点:观察性实验,于2005-11/2006-03在大连理工大学纳米复合材料研究实验室完成.材料:应用直流电弧等离子体法制备纳米镍粉,硅酸钠由天津市石英钟厂霸州市化工分厂生产.方法:以硅酸钠为主要原料,通过液相沉淀法在纳米镍粉表面包覆了一层SiO2.主要观察指标:应用X射线衍射仪、傅里叶红外光谱仪、透射电镜、振动样品磁强计、热重分析仪等对复合粉体的结构、形貌和磁性能进行检测.结果:SiO2以非晶态的形式包覆在纳米镍粒子表面,形成了核壳结构,降低了纳米粉体的团聚现象.经SiO2包覆后纳米镍粉氧化温度由287℃提高到385℃.磁性分析结果表明,粉体包覆前由于表面氧化层(NiO)的存在,粉体的磁滞回线偏移;包覆后的粉体由于SiO2的存在,饱和磁化强度降低,矫顽力升高.结论:成功制备了SiO2/Ni核壳结构纳米粒子,SiO2的包覆提高了纳米粉体的抗氧化性,且纳米镍粉具有很好的铁磁性能,矫顽力升高.     

Structural transition and magnetic properties of Mn doped Bi0.88Sm0.12FeO3 ceramics

We investigated the effects of Mn doping on the crystal structure, phonon vibration, and magnetic properties of Bi_0.88Sm_0.12FeO₃ ceramics. Mn doping effectively modified the rhombohedral symmetry and induced a structural transition from an R3c rhombohedral to Pnam orthorhombic structure. Magnetic measurements revealed a weak ferromagnetic behavior, which was related to the canted antiferromagnetic order of the Pnam structure. The cycloidal spin structure of the R3c phase could not be suppressed by substitution of Mn at the Fe site. Studies on the self-phase transition and electric field-induced structural transition revealed many changes in coercivity and remanent magnetization, which are believed to originate from the R3c/Pnam phase switching along with spin frustration. Observations of the field step-dependent hysteresis loop and the ferromagnetic-like hysteresis loop after poling in an electric field provided direct evidence of phase boundary (PB) ferromagnetism and magnetic coupling at the PB.

We investigated the effects of Mn doping on the crystal structure, phonon vibration, and magnetic properties of Bi_0.88Sm_0.12FeO₃ ceramics.