Sol–Gel Synthesis of Mn–Sn–Ti-Substituted Strontium Hexaferrite Nanoparticles: Structural,Magnetic, and Reflection-Loss Properties

Substituted strontium hexaferrite nanoparticles with the chemical formula SrFe_12?x (MnSn_0.5Ti_0.5) _x/2O₁₉(x = 0–2.5, in a step of 0.5) were prepared by a sol–gel method. Phase identities and crystal structure of the synthesized nanoparticles were investigated by x-ray diffraction. The morphology of the nanopowders was determined by field emission scanning electron microscopy. Results obtained from Fourier-transform infrared spectroscopy revealed the presence of stretching and bending modes in the citrate complex. Mössbauer spectroscopy (M _S) revealed occupancy of the hexagonal lattice structure by non-magnetic Mn²⁺ –Sn⁴⁺ –Ti⁴⁺ cations. Magnetic properties were measured by use of a vibrating sample magnetometer. The results showed that saturation magnetization and coercivity decreased with increasing x content. Microwave absorption properties were investigated by use of a vector network analyzer. It was found that the maximum reflection loss of substituted Sr-ferrite 1.6 mm thick reached ?41.8 dB at a frequency of 4.3 GHz and a bandwidth of 7.5 GHz, with reflection loss being higher than ?25 dB. These results imply that the prepared composites are good candidates for absorbers in the gigahertz frequency range.     

Synthesis, Structures, and Multiferroic Properties of Strontium Hexaferrite Ceramics

Simultaneous occurrence of large ferroelectricity and strong ferromagnetism has been observed in strontium hexaferrite (SrFe₁₂O₁₉) ceramics. Strontium hexaferrite powders with hexagonal crystal structures have been successfully synthesized through the co-precipitation precursor method using strontium nitrate and ferric nitrate as starting materials. The powders were pressed into pellets and then sintered into ceramics at a temperature range of at 1000°C to 1100°C for 1 h. The structure and morphology of the ceramics were determined using x-ray diffraction and field-emission scanning electron microscopy techniques. Clear ferroelectric hysteresis loops demonstrated large spontaneous polarization in the SrFe₁₂O₁₉ ceramics at room temperature. The maximum remnant polarization of the SrFe₁₂O₁₉ ceramic was estimated to be approximately 15 μC/cm². The FeO₆ octahedron in its perovskite-like hexagonal unit cell and the displacement of Fe³⁺ off the center of the octahedron are proposed to be the origin of electric polarization in SrFe₁₂O₁₉. In our experimental observations, the SrFe₁₂O₁₉ ceramic also revealed strong ferromagnetism at room temperature.     

Effect of Heat Treatments on the Structural and Magnetic Properties of La-Co Substituted Strontium Ferrite Films

A sputter-deposited strontium ferrite film with perpendicular anisotropy has been developed. The film, composed of La_0.33Sr_0.67Co_0.25Fe_11.75O₁₉, has been fabricated directly on quartz glass substrates by radio frequency magnetron sputtering with various heat treatments. The structural and magnetic property dependence of those films on heat treatments has also been studied. The optimized condition is the heat treatment of in situ heating at 400°C and post-annealing at 850°C–900°C. When post-annealing temperature exceeds 900°C, parasitic phases of γ-Fe₂O₃ and LaFeO₃ appear and gradually increase; meanwhile, the magneto plumbite phase gradually decreases. High c-axis perpendicularly oriented films with the coercivity (4148 Oe), remanence squareness ratio (0.89) and perpendicular magnetic anisotropy energy density (1.65 × 10⁶ erg/cm³) are achieved, which is attributed to the single magneto plumbite phase with compact platelet grains and almost complete (0 0 l) texture of the c-axis normal to the film plane.     

Cu、Zn掺杂对Co2Y软磁铁氧体性能的影响

介绍了通过掺杂Cu、Zn离子对Co2Y(Ba2Co2Fe12O22)型平面六角结构软磁铁氧体的成相及其性能的影响。采用传统的固相反应法制备样品，Ba2Co1.2-xZnxCu0.8Fe12O22(x=0-1.2)的合成温度低，成相温度范围比较宽，易于成相。在甚高频段，对Ba2Co1.2-xZnxCu0.8Fe12O22的磁性能、介电性能及改善进行了深入的探讨。     

Study of the Structural,Optical, Dielectric and Magnetic Properties of Copper-Doped SnO2 Nanoparticles

Journal of Electronic Materials - This work explores the structural, optical and dielectric properties and the magnetic behaviour of copper (Cu) (0–4%)-doped tin dioxide (SnO2) nanoparticles,...     

Effect of Indium Substitution on the Thermoelectric Properties of Orthorhombic Cu4SnS4

We report the thermoelectric properties of Cu₄In _x Sn_1?x S₄ (x = 0–0.02), which undergoes a first-order structural phase transition at ~230 K. Substitution of In³⁺ for Sn⁴⁺ suppresses the phase transition temperature (T _t). Indium substitution reduces the electrical resistivity, and degenerate conduction by the orthorhombic phase is observed. The Seebeck coefficient increases over the whole temperature range and a maximum value occurs in the monoclinic phase as a result of indium substitution. Thermal conductivity decreases as x increases, which enhances the dimensionless figure of merit, ZT. We therefore expect optimization of the chemical composition of indium-doped Cu₄SnS₄ to result in an even larger ZT value.     

室温铁磁性Al2O3:Mn的制备及性质

以Al2O3为衬底利用多能态离子注入法在离子注入设备上制备了一系列具有室温铁磁性的Al2O3:Mn样品.在Al2O3的X射线衍射峰附近发现新的衍射峰,该衍射峰既可能对应一种未知新相,也可能对应Al2O3:Mn固溶体.所有样品都具有磁滞现象和室温铁磁性.     

室温铁磁性Al2O3∶Mn的制备及性质

以Al2O3为衬底利用多能态离子注入法在离子注入设备上制备了一系列具有室温铁磁性的Al2O3:Mn样品.在Al2O3的X射线衍射峰附近发现新的衍射峰,该衍射峰既可能对应一种未知新相,也可能对应Al2O3:Mn固溶体.所有样品都具有磁滞现象和室温铁磁性.     

Syntheses,Properties, and Potential Applications of Multicomponent Magnetic Nanoparticles

Multicomponent hybrid nanostructures that contain two or more nanometer‐scale components have attracted much attention recently owing to the synergistic properties induced by interactions between these different nanometer‐scale objects. Herein, we give an overview of the efforts to synthesize multicomponent nanoparticles with at least one component being magnetic, and focus on our recent developments. The syntheses are based on heterogeneous nucleation and growth of a second and third component onto seed nanoparticles. These multicomponent nanoparticles show interesting magnetic, magneto‐optical, plasmonic, and semiconducting properties that can be modulated by interfacial interactions between different nanocomponents. This opens up a new avenue to advanced multifunctional nanomaterials for device concepts and applications.     

Effects of Cu and Co Substitution on the Properties of NiZn Ferrite Thin Films

Cu-and Co-substituted NiZn ferrite thin films,Ni0.4-xZn0.6CuxFe2O4 and Ni0.5Zn0.5CoxFe2-xO4(0≤x≤0.2),are synthesized by sol-gel process.The crystallographic and magnetic properties of Cu-and Co-substituted NiZn ferrite thin films have been investigated.The lattice parameter decreases with Cu substitution and increases with Co substitution.The saturation magnetization decreases and the coercivity increases with the increase of Cu substitution.Moreover,the saturation magnetization gradually increases with the increase of Co substitution when x≤0.10,but decreases when x>0.10.Meanwhile,the coercivity initially decreases with the increase of Co substitution when x≤0.10,but increases when x>0.10.     

Magnetic and Structural Investigation of ZnSe Semiconductor Nanoparticles Doped With Isolated and Core‐Concentrated Mn2+ Ions

X‐Ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals (2–7 nm) are reported in order to study their local electronic structure and magnetic properties. ZnSe nanoparticles containing either single manganese ions (Mn²⁺) distributed in the lattice of the entire particle or a MnSe core in the center are prepared using high temperature approaches. The Mn²⁺ concentration is varied between less than one to several tens of manganese ions per nanocrystal. For all samples it is shown that the Mn²⁺ is exclusively present in the bulk of ZnSe nanoparticles with no evidence for oxidation to higher Mn‐oxidation states. The magnetic ions are highly polarized inside the nanocrystals reaching about 80% of the theoretical value of a pure d⁵ state under identical conditions for the case of isolated manganese ions. Nanocrystals with a MnSe core ZnSe shell structure reach <50% of this value. Thus, their polarization is significantly more hindered, which is due to the significantly enhanced Mn–Mn interactions and a more distorted crystalline lattice. In contrast, no coupling between the manganese centers is observed in the nanoparticles doped samples with low concentrations of Mn²⁺, indicating that these ions are isolated in the bulk of the nanoparticles.     

Cr离子取代Co2Z六角铁氧体的磁特性研究

采用固相反应法制备了Cr离子取代的Co2Z平面六角结构(Sr3Co2Fe24-xCrxO41)软磁铁氧体,并对其磁特性进行了研究。分析了样品的物相组成,并计算了样品的晶格常数;用扫描电镜分析了样品的形貌特征;测试了样品的磁滞回线。实验结果表明,掺杂Cr离子后,晶格常数变化不大,当Cr取代量x≥0.3时,Z相开始分解;在x≤0.2时,随着x的提高,样品的饱和磁化强度(Ms〖WTBZ〗)逐渐增加;当x＞0.2时,随着x的增加,样品的饱和磁化强度减小。由此可见,通过掺入适量的Cr离子可以提高Z型六角铁氧体的磁特性。