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1.
聚乙烯醇(PVA)溶胶凝胶法制备出CoFe 2O 4纳米微粉,用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe 2O 4纳米颗粒80—873 K的变温穆斯堡尔谱,发现纳米颗粒的磁转变温度范围为793—813 K,比块体材料的磁性转变温度要低.CoFe 2O 4纳米颗粒的德拜温度 θA=674 K, θB=243 K,比块体材料要小.CoFe 2O 4纳米颗粒超精细场 Hf随温度的变化符合 T3/2+ T5/2定理.当温度较高时,平均同质异能移IS随温度的升高而减小,并呈线性关系.
关键词:
纳米颗粒
磁性
穆斯堡尔谱 相似文献
2.
本文采用溶胶-凝胶工艺并结合脉冲激光沉积技术, 在Pt/Ti/SiO 2/Si衬底上制备了Co/Co 3O 4/PZT多铁复合薄膜. 对复合薄膜的微结构和组分进行了表征, 并系统研究了复合薄膜中的交换偏置效应及其对磁电耦合作用的影响. 研究结果表明, 复合薄膜在77 K具有明显的交换偏置效应, 交换偏置场达到80 Oe, 且交换偏置场及矫顽场均随温度降低而增大. 当温度降低到10 K时, 交换偏置场增至160 Oe. X射线光电子能谱(XPS)测试结果证实在Co和Co 3O 4界面处存在约5 nm厚的CoO层, 表明77 K下的交换偏置效应源自反铁磁的CoO层对Co的钉扎作用. 观察到复合薄膜的电容-温度曲线随着外加磁场大小和方向的改变而呈现出规律性的变化, 表明复合薄膜存在磁电耦合效应. 进一步研究发现, 在低温下复合薄膜呈现出各向异性的磁电容效应, 与磁场大小和方向密切相关. 复合薄膜的这种磁电耦合特性主要与复合体系的交换偏置效应及基于界面应力传递的磁电耦合作用有关, 本文对其中的物理机理进行了详细讨论与分析. 相似文献
3.
在90 ℃水溶液中采用两步晶体生长法制备出类花状ZnO-CoFe 2O 4复合纳米管束.ZnO纳米管束的管壁厚度大约为60 nm,管的直径大约为350 nm,CoFe 2O 4纳米颗粒连续包覆在ZnO纳米管束的表面,CoFe 2O 4纳米颗粒尺寸小于40 nm, 壳层厚度随着CoFe 2O 4在ZnO-CoFe 2O 4
关键词:
类花状
2O 4')" href="#">ZnO-CoFe 2O 4
纳米管束
微波吸收剂 相似文献
4.
在Si-Al 2O 3复合薄膜中观察到室温铁磁性.Si的体积百分比为15 %的Si-Al 2O 3复合薄膜的磁性最强.Si的含量影响样品的磁有序,在样品中观察到了明显的磁畴.在不同气氛下,对样品进行快速热退火.退火样品的磁性测试结果的差别表明氧空位不是样品铁磁性的主要来源.我们认为铁磁性来源于Si与Al 2O 3基质界面之间的缺陷的磁耦合.改变Si的含量可以改变缺陷密度,从而控制铁磁耦合强度.
关键词:
2O 3薄膜')" href="#">Al 2O 3薄膜
室温铁磁性
掺杂
交换相互作用 相似文献
5.
采用溶胶凝胶工艺在p-Si衬底上制备了SrBi 2Ta 2O 9/Bi 4Ti 3O 12复合铁电薄膜. 研究了SrBi 2Ta 2O 9/Bi 4Ti 3O 12复合薄膜的微观结构与生长行为、铁电性能和疲劳特性. 研究表明: Si衬底Bi 4Ti<
关键词:
2Ta 2O 9')" href="#">SrBi 2Ta 2O 9
4Ti 3O 12')" href="#">Bi 4Ti 3O 12
复合铁电薄膜
溶胶凝胶工艺 相似文献
6.
讨论了Ni 0.8Zn 0.2Fe 2O 4 (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成,再经900℃热压,并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级,并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时,横向ME电压系数(α E)的最大值变化范围为25.6 mV Am -2≤α E≤199.6 mV Am -2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合.
关键词:
镍铁氧体
PZT
热压法
ME效应 相似文献
7.
用射频/直流磁控溅射法制备了CeO 2/Nb 2O 5双层氧敏薄膜,利用X射线光电子能谱(XPS),描述并解释了单层CeO 2薄膜中氧随温度变化的动力学行为,以及CeO 2/Nb 2O 5薄膜界面对氧敏特性的影响.通过对Ce3d XPS谱的高斯拟合,计算了Ce 3+浓度并给出了判定Ce 4+还原的标志.结果表明,界面效应可以提高CeO 2/Nb 2O 5薄膜中Ce 4+的还原能力,使之远远高于单层CeO 2薄膜,这对薄膜的氧敏特性是极为有利的.
关键词: 相似文献
8.
采用传统的固相法制备了(1- x)(K 0.5Na 0.5NbO 3-LiSbO 3-BiFeO 3)- xCuFe 2O 4 ( x=0.1, 0.2, 0.3, 0.4) 磁电复合陶瓷, 并借助X射线衍射仪、扫描电镜和磁电耦合系数测试仪等对复合陶瓷的微结构和性能进行了分析. 结果表明, 复合陶瓷的K 0.5Na 0.5NbO 3-LiSbO 3-BiFeO 3和CuFe 2O 4物相之间发生了一定的离子相互扩散作用, 且两相的颗粒大小匹配性较好. 随着CuFe 2O 4含量增加, 复合陶瓷的压电系数从130 pC/N减小到30 pC/N, 饱和磁致伸缩系数从4.5×10 -6增加到12.4×10 -6左右, 磁电耦合系数表现出先增加后减小, 在 x=0.3时获得最大的磁电耦合系数9.4 mV·cm -1·Oe -1.
关键词:
0.5Na 0.5NbO 3-LiSbO 3-BiFeO 3')" href="#">K 0.5Na 0.5NbO 3-LiSbO 3-BiFeO 3
2O 4')" href="#">CuFe 2O 4
磁电耦合 相似文献
9.
通过助溶剂熔融法并在氩气气氛炉中成功生长出高质量大尺寸的CaTi 2O 4的单晶.X射线衍射实验及能量损失谱EDS证实,制备的CaTi 2O 4单晶晶胞参数 a=9.781?, b=9.966?, c=3.148?,所有样品均为单相,且符合化学计量比,样品高纯.通过直流磁化率的测量,首次给出了晶体的Van-Vleck顺磁因子为6.85×10 -5cm 3/mol,Cure-Weiss温度为-0.44 K,呈弱反铁磁性.同时,通过单晶各向磁化率的测量,进一步确认了CaTi 2O 4晶体中一维有序Ti-Ti反铁磁dimer链的形成,并明确了其方向.
关键词:
2O 4')" href="#">CaTi 2O 4
磁化率
各向异性
反铁磁二聚化 相似文献
10.
利用反滴共沉淀法制备了NiFe 2O 4纳米粒子,并在高压下(4.5GPa)压制成块状纳米固体材料.X射线衍射显示,NiFe 2O 4纳米固体的晶体结构和平均晶粒尺寸在高压下均没有发生变化.但其室温和低温穆斯堡尔谱结果表明,高压对纳米固体内部的磁相互作用和界面原子状态有很大的影响.在高压下,纳米固体内部的颗粒间磁偶极相互作用和界面离子间的超交换相互作用显著增强.从而明显抑制了NiFe 2O 4关键词: 相似文献
11.
The time-differential perturbed angular correlation technique has been used to study the temperature dependence of the electric-field gradient at 111Cd nuclei in the spinels CdFe2O4 and ZnFe2O4. The samples were doped with radioactive 111In tracers which decay to 111Cd by electron capture. For both compounds the results of the measurements show the presence of two electric quadrupole interactions. One is well defined and corresponds to a fairly symmetrical electric field gradient. The other is broadly distributed and corresponds to electric field gradients with lower symmetry. The fractions of probes associated with these interactions are temperature dependent. The interactions are analysed taking into account the possible sites in the spinel structure for In occupation. The results are compared with those obtained with other spinels. The electric field gradient associated with the octahedral site is compared with the predictions of point charge model and with Mössbauer spectroscopy results at iron site. 相似文献
12.
The aim of this study was to prepare a novel targeting nano drug delivery system of 2-methoxyestradiol (2-ME) based on the folic acid-modified bovine serum albumin, in order to improve the clinical application disadvantages and antitumor effect of 2-ME. In this study, 2-methoxyestradiol-loaded albumin nanoparticles (2-ME-BSANPs) were prepared by desolvation method, and then the activated folic acid was conjugated to 2-ME-BSANPs by covalent attachment (2-ME-FA-BSANPs). The size and zeta potential of 2-ME-FA-BSANPs were about 208.8 ± 5.1 nm and ?32.70 ± 1.01 mV, respectively. 2-ME loading efficiency and loading amount of the nanoparticles were 80.49 ± 3.80 and 10.25 ± 1.59 %, respectively. SEM images indicated that 2-ME-FA-BSANPs were of a round shape, similar uniform size, and smooth surface. Studies on drug release indicated that 2-ME-FA-BSANPs had the properties of sustained and controlled release, which provided them with the ability to fight continually against cancer cells. Internalization analysis demonstrated that 2-ME-FA-BSANPs-targeting drug delivery system could get efficiently transferred into the cells through the folic acid-mediated endocytosis, leading to higher apoptosis and affording higher antitumor efficacy against SMMC-7721 cells in vitro compared with 2-ME alone. Furthermore, the cell-cycle arrest of 2-ME-FA-BSANPs on the SMMC-7721 cells occurred at G2/M phase, and 2-ME-FA-BSANPs did not change the inhibition of the tumor mechanisms of 2-ME. Based on these results, it was concluded that albumin nanoparticles could be the promising nano carrier for 2-ME, and 2-ME-FA-BSANPs-targeting drug delivery system may be promising candidate for providing high treatment efficacy with minimal side effects in future cancer therapy. 相似文献
13.
The samples in two material systems, Na 2Mo 1? x W x O 4 and Na 2Mo 1? y S y O 4, were prepared by using conventional solid reactions and characterized by X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), and difference scanning calorimetry (DSC). The XRD and EDX data indicated that all the samples in both systems were in the solid solution range. The DSC data indicated that in the system Na 2Mo 1? x W x O 4, the solid–solid transition temperatures increased and in the system Na 2Mo 1? y S y O 4, the solid–solid transition temperatures decreased. The total enthalpy (Δ H total) of the solid–solid transitions in the system Na 2Mo 1? x W x O 4, decreased much less than that in the system Na 2Mo 1? y S y O 4. This is probably because similar to Na 2MoO 4, the solid–solid transition of Na 2WO 4 has relatively large Δ H total, but Na 2SO 4 has much smaller solid–solid transition enthalpy. In order to modify the transition temperatures of Na 2MoO 4 and also to keep its relatively large Δ H total, it is necessary to choose a doping material with large Δ H total. 相似文献
14.
Ferrites with the composition Mg 1−x
CO
x
Fe 2O 4(0< x≤0·33) were synthesized by solid state reaction between MgO, α-Fe 2O 3 and CoFe 2O 4 at 1300°C. The compounds were analyzed from the results of x-ray diffraction, magnetic hysteresis and initial susceptibility
( χ) studies. All the compounds of the series were found to be monophasic with no appreciable change in their lattice parameter.
The saturation magnetization and coercive field ( H
c
) values increased with increasing cobalt ferrite content. Similarly, the shapes of the χ-T curves and temperature variations of H
c
values indicated that the magnetic behaviour changes from multi-domain to single domain with increasing cobalt content. The
results are similar to those observed for the (MgFe 2O 4) 1−x
(Co 3O 4) system. 相似文献
15.
A detailed effects of catalyst X ( X?=?H 2O, (H 2O) 2, NH 3, NH 3···H 2O, H 2O···NH 3, HCOOH and H 2SO 4) on the HO 4H → O 3?+?H 2O reaction have been investigated by using quantum chemical calculations and canonical vibrational transition state theory with small curvature tunnelling. The calculated results show that (H 2O) 2-catalysed reactions much faster than H 2O-catalysed one because of the former bimolecular rate constant larger by 2.6–25.9 times than that of the latter one. In addition, the basic H 2O···NH 3 catalyst was found to be a better than the neutral catalyst of (H 2O) 2. However it is marginally less efficient than the acidic catalysts of HCOOH, and H 2SO 4. The effective rate constant ( k' t) in the presence of catalyst X have been assessed. It was found from k't that H 2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320?K at 0?km altitude. However, compared with the rate constant of HO 4H → H 2O?+?O 3 reaction, the k eff values for H 2O catalysed reaction are smaller by 1–2 orders of magnitude, indicating that the catalytic effect of H 2O makes a negligible contribution to the gas phase reaction of HO 4H → O 3?+?H 2O. Highlights -
A detailed effects of catalyst of H2O, (H2O)2, NH3, NH3···H2O, H2O···NH3, HCOOH and H2SO4 on the HO4H → O3?+?H2O reaction has been performed. -
From energetic viewpoint, H2SO4 exerts the strongest catalytic role in HO4H → O3?+?H2O reaction as compared with the other catalysts. -
At 0 km altitude H2O (at 100% RH) completely dominates over all other catalysts within the temperature range of 280–320 K. -
HO4H → H2O?+?O3 reaction with H2O cannot be compete with the reaction without catalyst, due to the fact that the effective rate constants in the presence of H2O are smaller. 相似文献
16.
Il Nuovo Cimento D - Two double-layered perowskitic compounds have been investigated by XRD analysis and Mössbauer spectroscopy. The experimental data allow the conclusion that magnetization... 相似文献
17.
We report the temperature dependence of the magnetic properties of (Ni, Cu)Fe 2O 4 spinel oxides. Mössbauer spectra for NiFe 2O 4 at various temperatures (79 ≤? T?≤ 900 K) are well fitted by two sextets associated with 57Fe nuclei at tetrahedral (A) and octahedral (B) sites. The Curie point T C was deduced by zero velocity Mössbauer technique to be 873 ± 3 K. The hyperfine fields are observed to vary with temperature according to the equation $B_{\rm hf} (T)=B_{\rm hf} (0)[{1-(T/T_{\rm C})^n}]^{\beta_n}$ where n?=?1 (based on the Landau–Ginzburg theory) and n?=?2 (based on the Stoner theory). A systematic decrease of the Mössbauer spectrum shift with increasing temperature is observed. 相似文献
18.
By making use of the diagonalization of the complete d^3 energy matriz in a trigonally distorted cubic-field and the theory of pressure-induced shifts (PS) of energy spectra,the whole energy spectrum of α-Al2O3:Mn^4 and PS of levels have been calculated.All the calculated results are in excdellent agreement with the experimental data.The comparison between the results of α-Al2O3:Mn^4 and ruby has been made.It is found that on one hand,R1-line and R2-line PS of α-Al2O3:Mn^4 and ruby are linear in pressure over 0-100 kbar,and their values of the principal parameter for PS are very close to each other.On the other hand,the sensitivities of R1-line and R2-line PS of α-Al2O3:Mn^4 are higher than those of ruby respectively,which comes mainly from the difference between the values of parameters at normal pressure of two crystals;moreover,the expansion of d-electron wavefunctions of α-Al2O3:Mn^4 with compression is slightly larger than the one of ruby,and the effective charge experienced by d-electrons of α-Al2O3:Mn^4 decreases with compression more rapidly than the one of ruby.In the final analysis,all these can be explained in terms of the facts that the two crystals are doped α-Al2O3 with two isoelectronic ions;the strengths of the crystal field and covalency of α-Al2O3:Mn^4 are larger than those of ruby respectively,due to the charge of Mn^4 to be larger than that of Cr^3 . 相似文献
19.
Crystalline [CuNd 2(C 4O 4) 4(H 2O) 16]·2H 2O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square
anion groups (C 4O 4) enter as bridge ligands, forming chains of neodymium ions interconnected by (C 4O 4)Cu(C 4O 4) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the
exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal
are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction
via hydrogen bonds is estimated to be ∼0.1 cm −1. As one proceeds from the high-temperature (250< T<300 K) to the low-temperature region ( T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal
is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by
the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The
magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J
Cu-Nd⩾0.2 cm −1. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra.
Fiz. Tverd. Tela (St. Petersburg) 39, 2057–2061 (November 1997) 相似文献
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