Fabrication and magnetic property of BaSm(x)Fe(12-x)O19 (x < or = 0.4) nanofibers

BaSm(x)Fe(12-x)O19 (x < or = 0.4) ferrite nanofibers were prepared by sol-gel method from starting reagents of metal salts and citric acid. These nanofibers were characterized by TG-DTA, FTIR, SEM, XRD and VSM. These results show that the BaSm(x)Fe(12-x)O19 (x < or = 0.4) ferrite nanofibers were obtained subsequently from calcination at 750 degrees C for 1 h. The BaSm(x)Fe(12-x)O19 (x < or = 0.4) microstructure and magnetic property are mainly influenced by chemical composition and heat-treatment temperature. The grain sizes of BaSm0.3Fe11.7O19 ferrite nanofibers are in a nanoscale from 40 nm to 62 nm corresponding to the calcination temperature from 750 degrees C to 1050 derees C. The saturation magnetization of BaSm(x)Fe(12-x)O19 ferrite nanofiber calcined at 950 degrees C for 1 h initially decreases with the Sm content from 0 to 0.3 and then increases with a further Sm content, while the coercivity exhibits a continuous increase from 348 kA x m(-1) (x = 0) to 427 kA x m(-1) (x = 0.4). The differences of magnetic properties are attributed to lattice distortion and enhancement for the anisotropy energy.     

Magnetic and magnetocaloric properties of nanocrystalline Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) manganites

Structural, magnetic and magnetocaloric properties of sol-gel prepared, nanocrystalline oxides Pr(1-x)A(x)Mn(1-y)Co(y)O3 (A = Ca, Sr) (x = 0.3; y = 0.5) (cubic, space group Fm3m) have been studied. From the X-ray data, the crystallite size of Pro.7Ca0.3Mn0.5Co0,503 and Pr0.7Sr0.3Mn0.5Co0.5O3 samples is found to be approximately 24 nm and approximately15 nm respectively. High resolution transmission electron microscopy image shows average particle size of approximately 34 nm and approximately 20 nm. Magnetization measurements indicate a Curie temperature of approximately 153 K and approximately172 K in applied magnetic field of 100 Oe for Pr0.7Ca0.3Mn0.5Co0.5O3 and Pr0.7Sr0.3Mn0.5Co0.O3 compounds. The magnetization versus applied magnetic field curves obtained at temperatures below 150 K show significant hysteresis and magnetization is not saturated even in a field of 7 T. The magnetocaloric effect is calculated from M versus H data obtained at various temperatures. Magnetic entropy change shows a maximum near T(c) for both the samples and is of the order approximately 2.5 J/kg/K.     

Structural & Magnetic Characterizations of NiLiZn Nanoferrites Synthesized by Co-precipitation Method

Synthesis of Ni0.5LixZn(0.5-x)Fe2O4 nanoparticles with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5 were realized via co-precipitation method. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements were performed on the samples to determine the characteristics of the crystal structures and the magnetic properties of the samples, respectively. The spinel phase structures of the samples were confirmed by XRD analysis. Patterns of decreased lattice parameter and increased crystallite size values were observed by increasing the Li concentration at longer synthesis reaction periods. Similarly, for the magnetic properties, both the saturation magnetization (Ms) and coercivity (Hc) were found to vary with increasing patterns at higher Li doping levels and longer synthesis reaction periods. The results and mechanisms concerned were discussed.     

Microstructure and magnetic property of M-type SrRe(x)Fe(12-x)O19 by sol-gel method

Magnetoplumbite-type (M-type) SrRE(x)Fe(12-x)O19 (RE = La and Ce, x = 0-1.0) powders were prepared by a citric acid sol-gel technique and subsequent heat treatment. The crystal structure, grain size and magnetic properties were investigated by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and vibrating sample magnetometer (VSM). The XRD patterns show that SrRE(x)Fe(12-x)O19 (RE = La and Ce) are mainly hexagonal magnetic plumbite structure, and the average grain size of 30-40 nm was calculated using the Scherer's equation based on the XRD spectrum. Substitution of Fe ion by the rare earth La ion causes a significant decrease in intrinsic coercivity (Hc) and a slight decrease in saturation magnetization (Ms) as shown in the magnetization hysteresis loops. However, the Hc rises gradually in a small wave pattern with the increase of doping content of the rare earth Ce. The relation between the crystal structure and magnetic properties was also studied in this work.     

Aliovalent-ion and magnetic field induced phase transition in multiferroic biFe(1-x)Ti(x)O3 system

Multiferroic compounds with general formula BiFe(1-x)Ti(x)O3 (x = 0.1, 0.2, 0.3 and 0.35) have been synthesized by conventional solid state reaction method. The effect of Ti substitution on ferroelectric and magnetic properties is studied. From X-ray diffraction (XRD) analysis, a rhombohedral to orthorhombic phase transition for x > 0.3 was observed. From SQUID measurements, a magnetic field induced phase transition has been observed in the BiFe(1-x)T(x)O3 system for x = 0.3. An anomaly in dielectric constant and dielectric loss in the vicinity of antiferromagnetic Néel temperature (T(N)) and a small enhancement in magnetization have been observed. Magnetization measurements above room temperature showed no systematic variation in antiferromagnetic Néel temperatures on Ti substitution. Further it is seen that this system shows the coupling between electric and magnetic dipoles exhibiting magnetoelectric (ME) effect at room temperature and possess high dielectric constant.     

Synthesis and microstructural characterization of Ce1-xTb(x)O2-delta (0 < or = x < or = 1) nano-powders

Ce1-xTb(x)O2-delta nano-powders have been successfully synthesized by using the ammonium carbonate coprecipitation method in an entire compositional range of 0 < or = x < or = 1 by adjusting the preparation conditions. Studies of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the powders with different compositions mainly consist of fluorite structure. In addition, a small amount of secondary phase was observed in the powders with x > or = 0.7. TEM observation indicated that the secondary phase could have a superstructure formed by a structural modulation of the fluorite structure.     

Mn_(0.2)Zn_(0.8)Fe_(2-x)Ce_xO_4铁氧体纤维的制备、结构及其磁性能

以柠檬酸和金属盐为原料,采用有机凝胶-热分解法成功制备了Mn0.2Zn0.8Fe2-xCexO4(x=0~0.04)系列铁氧体纤维。通过XRD、SEM和VSM等技术对产物进行了表征,研究了Ce3+掺杂对Mn-Zn铁氧体纤维的结构,微观形貌及磁性能的影响。结果表明,所制得的纤维轴向较为均匀,长径比较大,直径在0.5~3.5μm之间,组成纤维的晶粒平均尺寸为11.6~12.8nm。Ce3+掺杂没有引起Mn0.2Zn0.8Fe2-xCexO4纤维结构的明显变化,仍为单一的立方尖晶石结构,但晶格常数和晶粒粒径随Ce3+掺入量的增加而略微增大。Ce3+掺杂使Mn-Zn铁氧体纤维的饱和磁化强度增大,矫顽力下降,软磁性能有所提高。     

草酸-硝酸盐低热固相反应法制备(Ni_(0.58)Cu_(0.2)Zn_(0.22))Fe_(1.96)O_4铁氧体

以草酸和金属硝酸盐为原料,用低热固相反应法合成了纳米(Ni0.58Cu0.2Zn0.22)Fe1.96O4尖晶石型铁氧体,借助FT-IR、DSC-TG、XRD、TEM以及SEM等技术对固相反应过程和样品进行了研究及表征.FT-IR研究表明,草酸和金属硝酸盐在研磨过程中发生低热固相反应,生成金属草酸盐前驱体;FT-IR和XRD分析表明,前驱体经不同温度焙烧后得到单一尖晶石相的NiCuZn铁氧体粉末;依据TEM和SEM表征证明,前驱体在450℃分解1h后铁氧体粒径约为30～40nm,铁氧体于900℃烧结为陶瓷体后,晶粒约为2～4μml,烧结致密,磁谱测量表明,900℃烧结样品的磁导率为210,截止频率为28MHz.     

Structural and magnetic properties of Ni doped CeO2 nanoparticles

We report room temperature ferromagnetism in Ni doped CeO2 nanoparticles using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and dc magnetization measurements. Nanoparticles of Ce(1-x)Ni(x)O2 (0.0 < or = x < or = 0.10) were prepared by using a co-precipitation method. XRD measurements indicate that all samples exhibit single phase nature with cubic structure and ruled out the presence of any secondary phase. Lattice parameters, strain and particle size calculated from XRD data have been found to decrease with increase in Ni doping. Inter-planner distance measured from HR-TEM images for different Ni doped samples indicate that Ni ions are substituting Ce ions in CeO2 matrix. Magnetization measurements performed at room temperature display weak ferromagnetic behavior of Ce(1-x)Ni(x)O2 (0.0 < or = x < or = 0.10) nanoparticles. Magnetic moment calculated from magnetic hysteresis loop was found to increases with Ni doping up to 7% and then start decreasing with further doping.     

Synthesis, Characterization and Electromagnetic Studies on Nanocrystalline Nickel Zinc Ferrite by Polyacrylamide Gel

Nanocrystalline nickel zinc ferrite powders （Ni=Zn1-xFe2O4, A for x=0, B for x=0.2, C for x=0.5, D for x= 0.8 and E for x= 1） were synthesized by polyacrylamide gel method. X-ray diffraction （XRD）, transmission electron microscopy （TEM） and wave-guide were used to characterize the composition. The XRD results show that the dried gel powders are amorphous, and the characteristic peaks of the spinel Ni0.5Zn0.5Fe2O4 appear after the gel is calcined at 400℃ for 1 h. When the calcining temperatures are 600 and 800℃, the average grain sizes are identified by TEM to be 10 and 30 nm, respectively. The NixZn1-xFe2O4 powders have both dielectric loss and magnetic loss in the frequency range of 8.2-11.0GHz. With the increase of Ni^2＋ ions content, the dielectric parameters （ε′） and permeability （u′） of the NixZn1-xFe2O4 powders decrease while the dielectric loss （ε″）, magnetic loss （u″） and the reflection loss increase.     

微波多元醇法制备单分散Ni1-xZnxFe2O4/MWCNTs与磁性能

以多壁碳纳米管(MWCNTs)为模板,三乙二醇(TREG)为溶剂,采用微波多元醇法制备MWC-NTs负载组成可控的Ni1-xZnxFe2O4(x=0.4、0.5、0.6)纳米复合材料Ni1-xZnxFe2O4/MWCNTs。其结构和形貌通过XRD、SEM、TEM和EDX进行表征,用VSM测试样品的磁性,并探讨了微波功率、微波时间对镍锌铁氧体负载的影响。结果表明立方系尖晶石结构的单分散Ni1-xZnxFe2O4磁性纳米粒子均匀负载在碳纳米管表面,平均粒径约为6nm;其磁性能与镍锌铁氧体的组成有关,随着Zn含量的增加,饱和磁化强度(Ms)先增大后减小,当x=0.5时Ms达到最大值。矫顽力(Hc)都比较小,在室温下表现为超顺磁性。     

Nanoparticles of pure and substituted maghemites (gamma-M(x)Fe(2_x)O3 where M = Al, Cr, Mn, Zn and 0 < or = x < or = 1.3): a comparative study

Magnetic nanoparticles of pure and substituted iron oxides are prepared by single step autocombustion or by wet chemical methods. The nanoparticles prepared by the first process had mixed phase of hematite and maghemite whereas the later essentially gives maghemite phase. XRD patterns and TEM micrographs of the pure and substituted maghemites samples suggest about their monophasic nature and inverse spinel structure. Further, the size of the particles for the above iron oxide samples was found to be in the range of 4 to 30 nm. Saturation magnetization value for the samples was observed to be varying with the type and the amount of substitution. For example, magnetization value initially increased and then decreased for Al- and Mn-substitutions but it continuously decreased for Cr- and Zn-substitutions. Contrary to the saturation magnetization value, the Curie temperature decreased continuously with increased substitutions irrespective of the type of substitutions. Due to higher magnetization value of Mn-substituted maghemite (for x = 0.2, 78 Am2/kg), it has higher heating ability and specific absorption rate compared to Al-substituted maghemite (for x = 0.07, 70 Am2/kg) and pure maghemite (62 Am2/kg).     

Preparation and characterization of Ni-nitrilotriacetic acid bearing poly(methacrylic acid) coated superparamagnetic magnetite nanoparticles

Stable superparamagnetic magnetite (Fe3O4) nanoparticles were synthesized via co-precipitation in the presence of poly(methacrylic acid) (PMAA) in aqueous solution. The polymer coated Fe3O4 nanoparticles were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, thermal analysis, and vibrating sample magnetometry (VSM) techniques. These measurements reveal the presence of magnetite nanoparticles with a size of approximately 8 nm inside the PMAA matrix. The magnetization value of these superparamagnetic nanoparticles at room temperarure and 7 T was measured as about 40 emu/g. PMAA-coated Fe3O4 nanoparticles were further assembled with Ni-chelate through a reaction between a primary amine-bearing NTA (nitrilotriacetic acid) ligand and carboxy-functional groups of PMAA. NTA-PMAA-coated magnetite nanoparticles were then loaded with nickel ions and characterized using FTIR. The average amount of binded Ni on the surface of the NTA-modified PMAA coated Fe3O4 was calculated as 1.65 +/- 0.3 x 10(-6) mol nickel(II) ions per g of the magnetic particles from the inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements.     

Room temperature ferromagnetism in Fe-doped CeO2 thin films grown on LaAlO3 (001)

Ce_1 − xFe_xO_2 − δ/LaAlO₃(001) thin films (x = 0.01 and 0.03) have been prepared by pulsed laser deposition method and thoroughly characterized using X-ray diffraction (XRD), dc magnetization, near edge X-ray absorption fine structure (NEXAFS), and X-ray magnetic circular dichroism (XMCD). XRD data reveal a single-phase cubic structure with a strong crystallographic orientation along the (200) plane. Room temperature ferromagnetism is confirmed through isothermal hysteresis as well as temperature dependent magnetization measurements, which clearly show the ferromagnetic Curie temperature occurring at least above 350 K. The Fe L_3,2 edge NEXAFS spectra for both Fe-doped thin films exhibit mixed valent Fe²⁺/Fe³⁺ states, whereas Ce M_5,4 edge shows the 4+ state of Ce, throughout the doping. With the increase in Fe doping, Fe²⁺ state increases and a simultaneous decrease in magnetization value is also observed. The XMCD signal of both samples reveals the ferromagnetic ordering of substituted Fe ions in the ceria matrix. Our results indicate that ferromagnetism is intrinsic to the ceria system and is not due to any secondary magnetic impurity.     

Nanocrystalline sensor-grade Sn1-xInxO2 (0 < or = x < or = 0.2)

Nanocrystalline Sn1-xInxO2 (0 < or = x < or = 0.2) has been successfully prepared by a solution chemical route. High-resolution transmission electron microscopy studies show that the average grain size of Sn0.8In0.2O2 heated at 310 degrees C, 500 degrees C, and 800 degrees C for 12 h is about 3-4 nm, 5-6 nm, and 7-10 nm, respectively. The corresponding values for pure SnO2 are 3-4 nm, 7-10 nm, and 50-90 nm, respectively. Powder X-ray diffraction and electron diffraction studies confirm the existence of solid solution only in the nanocrystalline state (the average particle size is in the range of 5-10 nm) with the solubility limited to 20% of In2O3. Indium ions stabilize the nanocrystalline nature of Sn1-xInxO2 (0 < or = x < or = 0.2) and prevent the grain growth by entering the SnO2 lattice. The thermal characteristics of nanocrystalline Sn1-xInxO2 (0 < or = x < or = 0.2) investigated by thermogravimetric (TG) and differential thermal analysis (DTA) show that the solid solution decomposes at 820 degrees C into SnO2 and In2O3, which is accompanied by a rapid crystal growth. The electrical conductivity and activation energy of Sn1-xInxO2 (0 < or = x < or = 0.2) undergo significant changes when the average grain size is less than or equal to 2 x the Debye length, LD.     

Ni_(0.5)Zn_(0.5)Fe_2O_4铁氧体的制备及其电磁损耗性能

以Zn(NO3)2.6H2O、Ni(NO3)2.6H2O和Fe(NO3)3.9H2O及柠檬酸为原料,采用溶胶-凝胶法制备前驱体,在1 200℃下煅烧3 h合成ZnFe2O4和Ni0.5Zn0.5Fe2O4铁氧体粉体。利用差热分析、X射线衍射、扫描电镜、透射电镜和红外光谱等测试手段对产物进行分析和表征。结果表明:ZnFe2O4和Ni0.5Zn0.5Fe2O4属于立方晶系尖晶石结构,结晶完整,晶粒大小在100 nm左右。在0.2~1.8 GHz的频率下对产品进行了电磁损耗性能测试,发现Ni0.5Zn0.5Fe2O4具有较好的电磁损耗特性。     

Microstructure and magnetic properties of Fe(x)Ni(1-x) alloy nanoplatelets

Plate-like nanoparticles (or nanoplatelets) of Fe(x)Ni(1-x) (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) alloy were successfully synthesized through a simple sonochemical method. The shapes of the alloy nanoplatelets with different Fe atom contents are almost same. Their average diameters are about 50 nm, and their average thicknesses are several nanometers. The obtained Fe(x)Ni(1-x) alloy nanoplatelets are single-phased and have a face-centered cubic (FCC) crystal structure. The lattice constants of the alloy nanoplatelets are larger than the corresponding bulk value and increase with increasing Fe content. The surface oxidation of the alloy nanoplatelets leads to the lattice expansion. The alloy nanoplatelet powders are all ferromagnetic, and their saturation magnetizations are slightly lower than the corresponding bulk value. The saturation magnetic field and the coercivity increase with increasing Fe content. Magnetic hysteresis loops along the directions deviating different angles from the nanoplatelets plane are obviously different, indicating that the easy-axis is in the in-plane direction and the magnetization reversal is incoherent mode. The micromagnetic simulation results for the array composed of thirty-six Fe0.6Ni0.4 alloy nanoplatelets fit well with the measured data.     

Structural and magnetic study of a diluted magnetic semiconductor: Fe-doped CeO2 nanoparticles

This paper reports the effect of Fe doping on the structure and room temperature ferromagnetism of CeO2 nanoparticles. X-ray diffraction and the selective area electron diffraction measurements performed on the Ce(1-x)Fe(x)O2 (0 < or = x < or = 0.07) nanoparticles showed a single-phase nature with a cubic structure, and none of the samples showed the presence of any secondary phase. The mean particle size, which was calculated using transmission electron microscopy, increased with the increase in the Fe content. The DC magnetization measurements that were performed at room temperature showed that all the samples exhibited ferromagnetism. The saturation magnetic moment increased with the increase in the Fe content.     

Electrical properties of nanocrystalline Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) (0.1 < or = x < or = 0.3) ceramics for IT-SOFC

Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) (0.1 < or = x < or = 0.3) nano-sized powders were successfully synthesized by the solution combustion synthesis process. The calcined nanopowders showed a ceria-based single phase with a cubic fluorite structure. In this study, we discussed the structural and electrical characteristics of the sintered Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta). We obtained high-quality Ce(0.8)Sm(0.2)O(2-delta) and Ce(1-x)Gd(x)O(2-delta) ceramics with a high density, ultra-fine grain size, and high electrical conductivity even at low sintering temperature using the nanosized powders. The electrical conductivities at 800 degrees C for the Ce(0.8)Sm(0.2)O(2-delta) sintered at 1400 degrees C and the Ce(0.8)Gd(0.2)O(2-delta) sintered at 1350 degrees C were 0.110 and 0.104 Scm(-1), respectively.     

Magnetism in BiFe<Subscript>1−x</Subscript>Ni<Subscript>x</Subscript>O<Subscript>3</Subscript>: studied through electron spin resonance spectroscopy

The effect of Ni doping in BiFe_1?xNi_xO₃ (BFNO) multiferroics are studied by X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), hysteresis loop (M–H), temperature dependent magnetization (FC-ZFC) measurements and electron spin resonance (ESR) techniques. The XRD and FTIR studies indicate that the BFNO compounds remain in rhombohedral (R3c) phase without appearance of any structural transformation due to Ni doping. The XPS studies show the oxidation states of Fe ions as 3⁺, whereas Bi is found to be in a mixed valence state of 2⁺ and 3⁺ in BFNO. The Ni ion doping enhances the saturation magnetization from 0.179 emu/g (x?=?0.025) to 2.38 emu/g (x?=?0.20), which is higher than the reported values found in literature. The FC-ZFC magnetization studies suggest the presence of a magnetic phase transition from a weak ferromagnetic to a spin glass state at low temperature. The ESR studies confirm the ferromagnetic state of BFNO samples.