Synthesis and magnetic properties of SnFe2O4 nanoparticles

SnFe₂O₄ nanoparticles have been synthesized by the precipitation exchange method. X-ray diffractometry shows that the average size of the particles is 4 nm. The magnetization measurement has determined the existence of a paramagnetic state in this metal oxide system. As the temperature increases toward 350 K, Mössbauer line broadens and a pronounced central doublet appears, suggesting superparamagnetic relaxation.     

二氧化硅/MeFe_2O_4中空复合微球的制备、结构及其磁性能

采用磺酸基团官能化中空二氧化硅微球为模板,通过化学共沉淀法,将尖晶石铁氧体(MeFe2O4)包覆在中空二氧化硅微球表面,制备出二氧化硅/MeFe2O4中空复合微球。利用TEM、XRD和样品振动磁强计对中空复合微球的形貌、结构和磁性能进行表征。实验结果表明,通过调节三价铁盐与二价金属离子之间的比例可以将尖晶石铁氧体的粒径范围控制在15nm以下。所制备的复合中空微球具有优良的软磁性。当金属离子总浓度为0.10mol/L时,复合微球的饱和磁化强度可达9.75Am2/kg。     

Crystal structure and magnetic properties of Pr- and Ti-substituted La2RuO5

Polycrystalline samples of Pr- and Ti-substituted La₂RuO₅ were prepared applying a soft-chemistry route based on the thermal decomposition of citrate-stabilized precursors. The simultaneous substitution on the La-sites by Pr and on the Ru-sites by Ti results in samples of the composition La_2−xPr_xRu_1−yTi_yO₅ with 0 ≤ x ≤ 0.75 and 0 ≤ y ≤ 0.4. The crystal structures of these compounds were analyzed by Rietveld refinement of powder X-ray diffraction patterns. For pure La₂RuO₅ a structural transition from a monoclinic room-temperature modification to a triclinic low-temperature structure was found at 161 K. This structural change is linked to a low-temperature long-range ordered spin-singlet ground state formed by Ru⁴⁺ spin-moments. Both the structural transition and the formation of the singlet ground state become progressively suppressed with higher Ti contents, while the Pr substitution has only a minor influence on the dimerization. The behavior of the Curie–Weiss temperatures can be explained assuming two almost independent magnetic sublattices corresponding to the ruthenium and the rare-earth ions, respectively. For all investigated properties, i.e. crystal structure, magnetic susceptibilities, and dimerization temperature T_d, a completely additive behavior of the effects of Pr-substitution and Ti-substitution is observed.     

Crystal structure of NdLiP4O12

A single-crystal x-ray diffraction analysis has been performed on NdLiP₄O₁₂ synthesized by a flux method. The structure is monoclinic, with space group C 2/c, Z = 4, and cell parameters a = 16.408 (3), b = 7.035 (4), $\text{c}\text{= 9.729 (4)}\text{A}\text{?}$, and β = 126.38 (5)°. A full-matrix, least squares refinement gave R = 0.072, Rw = 0.077 for 590 independent reflections. The basic structural units are helical ribbons, (PO₃)_n, formed by corner-sharing of PO₄ tetrahedra. The NdO₈ dodecahedra are isolated from each other in the sense that they do not share any O atoms. This isolation accounts for the marked reduction in the concentration quenching of Nd⁺³ fluorescence that is observed for NdLiP₄O₁₂. The shortest Nd-Nd distance is 5.620 Å, and the concentration of Nd⁺³ ions is 4.42 × 10²¹ cm^?3     

CoCr2O4纳米晶的制备及其磁性研究

通过高分子金属络合物热解法制备了COCr2O4纳米晶，并对它的表面微结构和磁性能进行了表征。通过高分辨电镜和傅立叶红外光谱的研究发现在平均粒径为12nm的纳米晶表面不仅有晶格炔陷，而且吸附有大量聚合物分解后的有机碎片，这些有机碎片对纳米晶表面磁矩的钉扎以及纳米晶自身的表面晶格缺陷．导致自旋无序的表面和相对自旋有序的核之间产生强的交换耦合作用．从而使得纳料晶呈现出奇特的磁性能，如低温下存在较走的矫顽力和偏置场等。     

CoFe2O4纳米线阵列的合成及磁性

利用多孔阳极氧化铝模板和溶胶．凝胶法制备了CoFe2O4纳米线阵列。溶胶是通过真空注入法被填充到模板的纳米孔洞中的，通过高温热处理，形成CoFe2O4纳米线阵列。利用扫描电子显微镜（SEM）、X射线衍射仪（XRD）和振动样品磁强计（VSM）对CoFe2O4纳米线阵列的形貌、结构和磁性进行了研究。CoFe2O4纳米线的直径与模板孔径相等．其具有多晶的尖晶石结构。CoFe2O4纳米线阵列未表现磁各向异性，这是由其多晶结构和较大的磁晶各向异性常数决定的．     

热处理温度对纳米CoFe2O4/SiO2复合材料结构和磁性的影响

采用溶胶2凝胶法制备了纳米 Co Fe 2O 4/ SiO 2复合材料。利用 X射线衍射(XRD) 、 透射电镜( TEM) 、 振动样品磁强计(VSM)和 Mssbauer 效应研究了纳米复合材料结构、 晶粒尺寸及磁性。结果表明 , 样品中 Co Fe 2O 4的晶粒尺寸随着热处理温度的提高而增加 , 非晶态 SiO 2的存在有效地抑制了 Co Fe 2O 4晶粒的生长。VSM结果表明 , 样品的比饱和磁化强度和矫顽力随 Co Fe 2O 4晶粒尺寸的增加而变大。Mssbauer 效应结果表明 , 随着热处理温度的提高 , 样品从超顺磁和磁有序的混合状态转变为完全的磁有序状态。     

Crystal structure and magnetic properties of Cu4NiSi2S7

The structure of the compound Cu₄NiSi₂S₇ has been determined. It crystallizes in a new, monoclinic distorted sphalerite superlattice with the parameters: $\text{a}\text{= 11.551}\text{A}\text{?}$, $\text{b}\text{= 5.313}\text{A}\text{?}$, $\text{c}\text{= 8.165}\text{A}\text{?}$, β = 98.72°, $\text{V}\text{= 495.2}\text{A}\text{?}{}^3$, Z = 2, space group C2. The analogous compound Cu₄NiGe₂S₇ is isotypic. At a Neél temperature T_N = 20.2 K, Cu₄NiSi₂S₇ becomes antiferromagnetic. The magnetic moment of the paramagnetic phase is 2.6μ_B.     

Dielectric, magnetic and electrical properties of ZnFe2O4 ceramics

The polycrystalline sample of ZnFe₂O₄ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction studies of the compound showed the formation of a single-phase compound at room temperature. Studies of dielectric properties (ε_r, tan δ) of the above compound as a function of frequency in a wide temperature range show dielectric anomalies signifying existence of possible ferroelectric to paraelectric phase transition in the material. The confirmation of this assumption was made with observation of ferroelectric hysteresis loop at room temperature. Magnetic measurement exhibits anti-ferromagnetic nature of the sample. Studies of the zero-field cooled and the field-cooled magnetization in dc field provided the blocking temperature T_B. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between the microstructure (i.e., bulk, grain boundary, etc.) and electrical parameters of the material. Detailed studies of impedance parameters have provided an insight into the electrical properties and understanding of types of relaxation process in the material. The temperature variation of dc resistivity/conductivity exhibits negative temperature coefficient of resistance behaviour of the material. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.     

CuFe2O4/海泡石磁性吸附剂的制备及性能

以硫酸铜、氯化铁为主要原料,采用化学共沉淀法制备CuFe2O4纳米磁性微粒,然后将其与海泡石复合制得CuFe2O4载量不同(质量分数,下同)的磁性海泡石.分别用X射线衍射(XRD)、透射电子显微镜(TEM)、振动样品磁强计(VSM)对样品的物相、形貌、磁学性能进行了表征.结果表明,合成的CuFe2O4结晶度高,晶粒度约...     

Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

CuO/c-CuFe₂O₄ nanocomposites have been synthesized via the oxalate precursor route. Effect of synthesis conditions on the crystal structure, microstructure, magnetic and optical properties of the formed powders was studied. The results indicated that pure CuO nanoparticles were obtained from the oxalate precursor annealed at 600 °C for 2 h. However, substitution of Cu²⁺ ion by Fe³⁺ ion (Cu_1?X Fe _X O, where X = 0, 0.05, 0.1 and 0.2) led to form of CuO/CuFe₂O₄ nanocomposites. The microstructures of the powders appeared as a monoclinic like shape. Furthermore, the band gap energy of the obtained CuO nanopowders was 1.41 eV and the value was slightly decreased by Fe³⁺ ion substitution. In addition, the formed CuO particles had weak ferromagnetic characteristics. However, the substitution Cu²⁺ ion by Fe³⁺ ion enhanced the magnetic properties of the formed composite as the result of increasing the CuFe₂O₄ phase formation. Hence, the saturation magnetization was increased from 0.13 to 9.8 emu/g by increasing the Fe³⁺ ion from 0 to 0.2.     

Fe3O4缓冲层对CoFe2O4薄膜磁性能的影响

采用射频磁控溅射在基片Si（100）和Fe3O4（20nm）/Si（100）上制备了钴铁氧体（CoFe2O4）薄膜，制备的薄膜在空气气氛中进行300～1000℃的退火处理，采用XRD、VSM分析了薄膜的微结构以及磁性能。结果表明，制备的钴铁氧体薄膜均具有尖晶石结构，Fe3O4缓冲层薄膜促进了钴铁氧体薄膜的结晶，但降低了钴铁氧体薄膜的垂直各向异性和垂直于膜面方向的矫顽力，而钴铁氧体薄膜的磁化强度和矩形度得到了一定的提高。     

CoFe2O4纳米线阵列的制备与磁性

在氧化铝模板的纳米孔洞中,用电化学的方法沉积钴铁合金纳米线,经过550℃、30h氧化处理,成功制备出钴铁氧体纳米线阵列.分别用透射电子显微镜(TEM)、X射线衍射仪(XRD)和振动样品磁场计(VSM)对样品的形貌、晶体结构和磁学性质进行了表征测试.TEM观察结果显示纳米线粗细均匀,直径约为70nm.XRD显示纳米线的物相结构为CoFe2O4;VSM测试结果表明,CoFe2O4纳米线阵列的磁滞回线矫顽力为1.190×105A/m,比氧化处理前的钴铁合金纳米线阵列有显著提高.     

EuCuOSe: Crystal structure refinement, electrical and magnetic properties

The europium copper oxyselenide EuCuOSe has been prepared by reacting Eu, CuO and Se in the ratio 1:1:1 at 1123 K for a period of 10 days in sealed quartz ampoule. The structure has been determined by single-crystal X-ray methods. The compound crystallizes tetragonal in the space group P4/nmm (no. 129) with two formula units in the cell with dimensions a = 393.65(8) pm and c = 871.80(17) pm. The structure is composed of double layers separated by copper atoms, which are tetrahedrally coordinated to Se²⁻ anions. According to the resistivity measurements, EuCuOSe is a semiconductor. The magnetic susceptibility data shows the typical non-Curie-Weiss behavior of the ⁷F_J states of Eu in the 4f⁶ configuration.     

核壳型磁性纳米复合材料Fe3O4@SiO2@mTiO2@Pt的制备及催化性能

采用溶剂热法制备磁性Fe₃O₄粒子。碱性条件下,以Fe₃O₄为核采用Stober法和溶胶-凝胶法在其表面依次包覆SiO₂和介孔（m）TiO₂,通过3-氨丙基三甲氧基硅烷（APTES）对其表面修饰后,采用乙二醇的多羟基还原性,将Pt原位还原负载在Fe₃O₄@SiO₂@mTiO₂表面合成核壳型磁性纳米复合材料Fe₃O₄@SiO₂@mTiO₂@Pt。通过透射电子显微镜（TEM）、X射线粉末衍射仪（XRD）、紫外可见分光光度计（UV-Vis）、振动样品磁强计（VSM）及X射线光电子能谱分析仪（XPS）对样品的微观形貌、结构、磁性、元素组成等进行表征。以对硝基苯酚（4-NP）和罗丹明6G为目标污染物,研究Fe₃O₄@SiO₂@m...     

Effects of Gd2O3 on structure and magnetic properties of Ni-Mn ferrite

The emulsion method was used to prepare nanocrystalline Ni_0.7Mn_0.3Gd _x Fe_2-x O₄ ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd₂O₃ on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can’t enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd³⁺ ions are larger than that of Fe³⁺ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm.     

尖晶石型CoFe2O4/TiO2磁性光催化剂的制备及其性能

首先采用化学共沉淀法制备尖晶石型CoFe2O4,然后采用溶胶-凝胶法与钛酸丁四酯复合制备不同CoFe2O4载量(质量分数,下同)的CoFe2O4/TiO2磁性光催化剂。再利用X射线衍射(XRD)、透射电子显微镜(TEM)、振动样品磁强计(VSM)、同步热分析仪(TG-DSC)和紫外可见吸收光谱(UV-Vis)分别对物相、形貌、磁学性能等进行了分析和表征。最后在300 W紫外灯(主波长为253.7nm)照射下降解一定浓度的甲基橙溶液,研究不同CoFe2O4载量的CoFe2O4/TiO2磁性光催化剂在相变温度下对甲基橙溶液降解效果。结果表明,合成的CoFe2O4结晶度高,粒径为10～20nm,具尖晶石结构。CoFe2O4能较为均匀地负载于TiO2表面,CoFe2O4/TiO2磁性光催化剂具有超顺磁性。CoFe2O4/TiO2磁性光催化剂对甲基橙降解性能随CoFe2O4载量增加而降低。     

Synthesis of SiO2-coated ZnMnFe2O4 nanospheres with improved magnetic properties

A core-shell structured composite, SiO2 coated ZnMnFe2O4 spinel ferrite nanoparticles (average diameter of approximately 80 nm), was prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of ZnMnFe2O4 nanoparticles (average diameter of approximately 10 nm) synthesized by a hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The magnetic measurements were carried out on a vibrating sample magnetometer (VSM), and the measurement results indicate that the core-shell samples possess better magnetic properties at room temperature, compared with paramagnetic colloids with a magnetic core by a coprecipitation method. These core-shell nanospherical particles with self-assembly under additional magnetic fields could have potential application in biomedical systems.     

Crystal structure,microwave dielectric properties,and dielectric resonant antenna studies of novel low-permittivity CoAl2O4 spinel ceramics

CoAl₂O₄ spinel ceramics were prepared via a standard solid-state reaction method, and their crystal structure, microwave dielectric properties, and dielectric resonant antenna applications were systematically investigated in this study. X-Ray diffraction patterns and Raman spectra confirmed that CoAl₂O₄ belongs to the Fd-3 m space group with cubic crystal symmetry. ε_r and Qf values increased with the increasing sintering temperature, where an ever-improving microstructure was also observed from the scanning electron micrographs. The optimal microwave dielectric properties were achieved as follows: ε_r?=?9.34, Qf?=?30,500 GHz, and τ_f?=??54 ppm/^°C. Moreover, a dielectric resonant antenna was designed and simulated to demonstrate the application prospects of CoAl₂O₄ ceramics towards microwave antennas. The CoAl₂O₄-based antenna resonating at 14.33 GHz exhibited a high return loss of??40.9 dB, a wide impedance bandwidth of 940 MHz, and an exceptionally high total efficiency of 96.6%. The remarkable antenna performances suggested that CoAl₂O₄ ceramics were promising candidates for wireless communication devices operating at the Ku-band, provided τ_f can be further tuned toward zero.