掺Dy3+铁氧体纳米磁颗粒尺寸与磁学特性的相关性

在水相体系中用化学法制备出不同尺寸的掺Dy3+铁氧体纳米磁颗粒。采用透射电子显微镜(TEM)、X射线衍射仪(XRD)、超导量子干涉仪(SQUID)表征了样品的形貌、结构、室温磁学性能。TEM图片表明,样品的形貌近似球形,平均粒径在15～24nm之间;XRD图谱表明,磁颗粒的物相以Fe3O4为主,结构为面心立方尖晶石型;SQUID测试结果表明,磁颗粒的尺寸不同则磁学特性有所不同,呈现出饱和磁化强度(Ms)随粒径增大而升高的规律;粒径小则剩余磁化强度(Mr)、矫顽力(Hc)小,粒径增大则剩余磁化强度、矫顽力升高。     

Tb0.4Dy0.6(Fe1-xMnx)1.91(x=0,0.05,0.1 0,0.15)合金的磁致伸缩性能

研究了Mn替代Fe对多晶Tb0.4Dy0.6Fe1.91合金棒材性能的影响.分析了Tb0.4Dy0.6(Fe1-xMnx)1.91(x=0,0.05,0.10,0.15)多晶棒材的结构、晶格常数、居里温度和磁致伸缩性能,发现Mn替代Fe后,样品仍然为MgCu2型Laves相结构.随着Mn含量从0增加到0.15,样品的晶格常数从7.335A增加到7.347A,居里温度从668K降低到526K.Mn原子的替代通过改变材料的交换相互作用、总磁矩和易磁化方向影响材料的磁致伸缩性能.实验结果显示,Tb0.4Dy0.6(Fe1-xMnx)1.91样品在石=0.10时综合性能最好.     

化学还原法制备Fe3O4纳米颗粒及其性能研究

采用化学还原法制备得到了Fe3O4纳米颗粒,并用XRD对制备条件:分散剂种类、分散剂用量、煅烧温度、煅烧时间进行了研究。研究结果表明,当选用PEG(6000)做分散剂,PEG用量为50g/L,煅烧温度为700℃,煅烧时间为120min时,制备得到的Fe3O4纳米颗粒已经具有晶型完整的反尖晶石结构。将该样品做VSM分析,分析结果表明样品饱和磁化强度可达85A.m2/kg,并且矫顽力趋近于0,呈现出良好的顺磁性。     

环境温度对纳米掺镝铁氧体颗粒磁特性的影响

在水相体系中用化学共沉淀法制备出纳米掺镝铁氧体磁颗粒,利用透射电镜(TEM)观察了磁颗粒的形貌,X-射线衍射仪(XRD)确定了产物的相结构,超导量子干涉仪(SQUID)测试了样品的磁性能。在318～378K范围内,研究了温度变化对产物磁特性的影响。TEM图片和XRD图谱分析表明,样品的形貌近似球形,具有立方尖晶石型结构,平均粒径约18 nm左右。对产物的磁性能研究显示,318K时的饱和磁化强度(MS)为183.4 mT,温度升高MS呈现出降低的变化规律;318K时的矫顽力(HC)为0.345 mT,温度升高HC减小,超顺磁性的特性增强。     

Sm2O3掺杂(Ba0.7Ca0.3)TiO3-Ba(Zr0.2Ti0.8)O3无铅压电陶瓷的制备与性能

采用固相合成法制备了Sm2O3掺杂的(Ba0.7Ca0.3)TiO3-Ba(Zr0.2Ti0.8)O3(BCZT)无铅压电陶瓷.借助XRD、SEM等手段对该陶瓷的显微结构与电性能进行了研究.结果表明,Sm2O3的掺杂降低了BCZT无铅压电陶瓷的烧结温度并使居里温度点Tc从85℃提高到95℃.当Sm2O3掺杂量为0.02wt%～0.1wt%时,样品具有典型ABO3型钙钛矿结构.Sm2O3掺杂量为0.02wt%时,所得陶瓷样品具有最优综合电性能,其压电常数d33、机电耦合系数kp、机械品质因子Qm、介电损耗tanδ和介电常数εr分别为590 pC/N、0.52、43、1.3%和3372.     

水热法制备CoFe2O4纳米颗粒及其穆斯堡尔谱与磁性能研究

用水热法在不同温度下制备结晶性较好、颗粒均一的CoFe2O4纳米颗粒,无需进一步煅烧。利用X射线衍射仪(XRD)、场发射扫描电镜(SEM)、穆斯堡尔谱仪和综合物性测量系统(PPMS)对不同温度下合成的样品进行表征。结果表明,随着合成温度的升高,CoFe2O4纳米颗粒的结晶性增强,粒径逐渐增大,样品的饱和磁化强度逐渐增强。当合成温度为500℃时,CoFe2O4纳米颗粒的饱和磁化强度达到64.1A.m2/kg,与块体的CoFe2O4(72A.m2/kg)接近。穆斯堡尔谱分析表明,当晶粒粒径超过了超顺磁性的临界尺寸,样品的超顺磁性消失,随着合成温度的升高,B位上Fe3+离子的比例增高,磁性能增强。     

CoFe2O4-SiO2电纺纳米纤维的对喷制备技术与磁性研究

将溶胶-凝胶法和新型双喷丝头静电纺丝技术相结合,制备了CoFe2O4-SiO2电纺纳米纤维材料。利用热分析法(TG-DTA)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和振动样品磁强计(VSM)等测试手段,表征了所研制纳米纤维的晶型结构、纤维形貌以及磁学性能。研究结果表明,样品中CoFe2O4为单畴结构,纤维直径在100nm左右,非晶态SiO2的存在有效抑制了CoFe2O4晶粒的生长;煅烧温度对纤维形貌和晶型结构有较大影响,随着煅烧温度的升高,饱和磁化强度(Ms)和剩余磁化强度(Mr)均增大,但矫顽力(Hc)和剩磁比(Mr/Ms)呈波动变化。     

非晶Tb/Fe/Dy和Fe/Tb/Fe/Dy纳米多层膜磁性能及超磁致伸缩性能(英文)

研究非晶Tb/Fe/Dy(样品A)和Fe/Tb/Fe/Dy(样品B)纳米多层膜超磁致伸缩性能和磁性能.磁滞回线表明样品A的垂直磁各向异性而样品B有面向磁各向异性,样品B比样品A更好的磁性能.样品B有很好的低场超磁致伸缩性能,在外磁场为0.12T情况下样品B的超磁致伸缩性能是样品A的五倍,即从16ppm变为82ppm.     

电纺纳米纤维自组装制备含多磁性内核的Fe3O4@SiO2核壳结构纳米粒

通过电纺纳米纤维自组装制备了含多磁性内核的Fe3O4@SiO2核壳结构纳米粒。采用扫描电镜(SEM)表征了电纺纳米纤维的形貌,利用场发射扫描电镜(FE-SEM)、透射电镜(TEM)、傅里叶红外光谱仪(FT-IR)、X晶体衍射仪(XRD)和振动样品磁强计(VSM)分别对纳米粒的形貌、粒度分布、物相组成、化学成分和磁性能等进行了表征。结果显示:采用电纺纳米纤维自组装制备的Fe3O4@SiO2纳米粒为近似球形的结构,其内含有多个磁性内核;粒径分布在50nm左右,主要物相是无定形的SiO2和晶态的Fe3O4,保持了磁性粒子的超顺磁性,是一种优良的生物磁性材料。     

Pr0.15Tb0.3Dy0.55Fe1.85棒材的制备与性能研究

采用改进的区熔法和粘结法制备了Pr0.15Tb0.3Dy0.55Fe1.85棒材,并对棒材的磁致伸缩进行了研究.利用石英管作为熔体的载体对区熔法进行了改进,并采用该方法制备出＜110＞取向的Pr0.15Tb0.3Dy0.55Fe1.85棒材,沿棒材的＜110＞方向进行磁致伸缩的测量,当磁场为900kA/m时,磁致伸缩达到1000ppm.采用粘结法制备的Pr0.15Tb03Dy0.55Fe1.85棒材,电阻率较合金提高了近3个量级.变温磁致伸缩的测量表明172K至372K范围内,磁致伸缩随温度的升高而降低.     

Irreversible Magnetic Properties of Ceramic Hgba2Ca2Cu3O8 at Very High Pulsed Magnetic Fields

The magnetic properties of ceramic HgBa₂Ca₂Cu₃O₈ have been investigated using pulsed magnetic fields up to 50 tesla. The irreversibility line H _irr (T) and the magnetic critical current J _c,m (H,T) have been extracted from the high field hysteresis loops. Irreversibility fields exceed available fields at temperatures below 15 K. The magnetic critical current J _c,m is strongly dependent on the granular structure of the ceramic superconductor. This is reflected in the moderate value of the critical current density and its significant field dependence.     

Magnetic properties of NiSb2O4

The magnetic transition of the antimony oxide NiSb₂O₄ has been studied using heat capacity measurements and magnetic susceptibility data. The Néel temperature previously evaluated from neutron diffraction is confirmed: T_N = 45 ± 1 K. The entropy excess ΔS(20 – 60 K) associated with the transition is calculated and compared with the theoretical value. The susceptibility data are interpreted in terms of a Curie-Weiss law (θ_p = − 98K, M_eff = 3.98 μ_ß). Exchange integrals are evaluated.     

Magnetic anisotropy of V3O5

The magnetic anisotropy of V₃O₅ was investigated by magneto-torque measurements in the temperature range from 4.2 to 300 K. It has been confirmed that the Néel temperature is about 75 K and that two of the three principal axes vary with temperature in both the paramagnetic and antiferromagnetic states. The results are explained on a simplified four-sublattice model.     

Magnetic characterization of antiferromagnetic Ba2Fe6O11

The magnetic properties of the metastable compound Ba₂Fe₆O₁₁ present in the phase subsystem BaFe₂O₄ - BaFe₁₂O₁₉ have been analyzed by means of Mössbauer and magnetic measurements. The obtained data indicate that Ba₂Fe₆O₁₁ is a complex antiferromagnet with Neél temperature T_N = 488 K. The overall features of the Mössbauer spectra and the population of the observed iron sublattices suggest for Ba₂Fe₆O₁₁ a crystalline structure related to that of perovskite like compounds, which are often present in the chemical reactions that lead to the formation of hexaferrites. The extraneous phases present in the obtained samples, one of which turned out to be barium hexaferrite, have also been characterized.     

Magnetic properties of BaFe12O19 smallparticles

The magnetic properties of small BaFe₁₂O₁₉ particles about 50 nm in size have been studied; the emphasis was on small-size effects. The compound formation of the hexagonal structure was made at a relatively low temperature; the small particle size made this result possible. As compared to the bulk value, a significantly reduced saturation magnetization is observed for these particles; this agrees with similar reports made earlier by several authors. To examine these phenomena further, Mossbauer spectra were obtained with high magnetic field applied longitudinally (H_ex=16.4 and 50 kOe). The spectra show the presence of recalcitrant spins where the spin configuration has a noncollinear arrangement that even a 50-kOe magnetic field does not remove. This hard-to-saturate component may lie in the surface layer of the Ba-ferrite small particles. The data also provide evidence that the Fe ions in the bipyramidal (2b) sites undergo magnetic-field-induced oscillations at 4.2 K     

Magnetic properties of metallic La2CuO4

X-ray, magnetic susceptibility, and electron paramagnetic resonance measurements have been made on La₂CuO₄. Magnetic measurements in the range 4.2 – 300 K are consistent with the metallic nature of La₂CuO₄, and the itinerant - electron susceptibility is estimated to be 239 × 10^?6 emu mol^?1. The high susceptibility and density of states indicate that the conduction band is narrow. The results are discussed in terms of previous models of the level structure of La₂CuO₄, and it is concluded that conduction occurs via a $\text{σ1}{}_{\mathrm{<mtext>x</mtext>}}\text{2}{}_{\mathrm{<mtext>?</mtext><mtext>y</mtext>}}\text{2}$ band. Comparison of La₂CuO₄ with semiconducting lanthanide cuprates suggests that this compound is on the verge of a semiconductor-to-metal transition.     

团簇NiCo2S4的磁学性能

为探究团簇NiCo₂S₄的磁学性能,本文依据密度泛函理论(DFT)在B3LYP/Lan12dz水平下对团簇NiCo₂S₄进行优化计算,确定了三重态下的6种优化构型,并从轨道成单电子数、自旋布居数、磁矩、自旋密度差、轨道态密度图多个角度对构型进行分析。研究表明:团簇NiCo₂S₄的6种构型中,构型2^{(3)性能最优异,而热力学稳定性最好的构型1(3)在磁学性能方面表现一般,其余构型磁学性能相近。对于团簇NiCo₂S₄的磁性强度,在原子轨道上,s、p轨道对团簇NiCo₂S₄整体的磁性强度贡献较小,d轨道对整体的磁性强度贡献最大;Ni原子和自旋向上的α成单电子是团簇整体磁性强度的主要贡献者,其中,s轨道成单电子数的主要贡献者是S原子,p、d轨道主要是金属原子,Ni原子d轨道主要受α成单电子影响,Co、S原子既受α成单电子的影响又受β成单电子的影响。团簇NiCo₂S₄作为磁性材料时采用构型2(3)}作为模型基础,可以通过增大金属Ni比例来增强磁性。     

Magnetic ordering in Zn substitutedCo1.4Ge0.4Fe1.2O4 spinelsystem

A systematic study of the Co_1.4Ge_0.4Fe_1.2O₄ system by X-ray, magnetization, and AC-susceptibility techniques is presented. The present system exhibits para-ferri-cluster spin glass transition for x⩽0.2, while x⩾0.3 it exhibits only a cluster spin glass transition. The AC susceptibility and DC magnetization data support the cluster spin glass ordering in the system. The system exhibits local spin canting behavior     

Magnetic properties of melt spunSmFe11Ti-Sm2TM17 pseudobinary alloys

Several alloys in the SmFe₁₁Ti-Sm₂TM₁₇ (TM=Co/Fe/Cu/Zr) pseudobinary system containing O-90 wt.% Sm₂TM₁₇ were prepared by the melt spinning technique. A maximum as-spun coercivity of 4.6 kOe was obtained for the alloy containing 10 wt.% Sm₂TM₁₇ at a substrate velocity of 15 m/s. The coercivity is enhanced to 5.3 kOe after annealing at 800°C for 1 h. XRD (X-ray diffractometry) and TEM (transmission electron microscopy) were used to investigate the microstructure of the alloys. It is suggested that the grain refinement, doping of the 1-12 phase with Sm and other elements, and reduced free iron might be the main causes coercivity enhancement     

Magnetic properties of melt spun NdFe10Cr2-Nd0.67B0.33 pseudobinary alloys

The coercivity of the melt-spun pseudobinary (NdFe₁₀Cr ₂)_1-x (Nd₂B)_x alloys, in which Nd₂B represents a composition of Nd_0.67B_0.33, was systematically studied. It was found that significant coercivities are possible with optimal additions of the Nd-B composition at x=0.5-0.7. The as-spun (substrate velocity=10 m/s) coercivity increased from 0.1 kOe at x=0.0 to maxima of 7.0 and 7.5 kOe at x=0.5 and 0.7, due to the Nd₂ Fe₁₄B and a new Fe-Nd phase, respectively, as evidenced from thermomagnetic analysis and X-ray diffraction. Annealing the overquenched amorphous x=0.7 alloy led to the crystallization of the Nd₂Fe₁₄B phase, and a coercivity of 8.5 kOe was obtained