Zn1-xCoxO稀磁半导体薄膜的结构及其磁性研究

利用X射线吸收精细结构、X射线衍射和磁性测量等技术研究脉冲激光气相沉积法制备的Zn_1-xCo_xO (x＝0.01,0.02)稀磁半导体薄膜的结构和磁性.磁性测量结果表明Zn₁-xCo_xO样品都具有室温铁磁性.X射线衍射结果显示其薄膜样品具有结晶良好的纤锌矿结构.荧光X射线吸收精细结构测试结果表明,脉冲激光气相沉积法制备的样品中的Co离子全部进入ZnO晶格中替代了部分Zn的格点位置,生成单一相的Zn_1-xCo_xO 稀磁半导体.通过对X射线吸收近边结构谱的分析,确定Zn_1-xCo_xO薄膜中存在O空位,表明Co离子与O空位的相互作用是诱导Zn_1-xCo_xO产生室温铁磁性的主要原因. 关键词： 1-xCo_xO稀磁半导体')" href="#">Zn_1-xCo_xO稀磁半导体 X射线吸收精细结构谱 脉冲激光气相沉积法     

ZnCoO稀磁半导体的室温磁性

采用固相反应法，将ZnO和Co₂O₃粉末按不同的成分配比混合，制备了稀磁半导体Zn_1-xCo_xO (x=0.02,0.06,0.10)材料.并使用H₂气氛退火技术对样品进行了处理，得到了具有室温铁磁性的掺Co氧化锌稀磁半导体.利用全自动X射线衍射仪、X射线光电子能谱仪、高分辨透射电子显微镜和超导量子干涉器件磁强计对样品的结构、晶粒的尺寸、微观形貌以及磁性等进行了测量和标度. 关键词： 稀磁半导体 氧化锌 掺杂 固相反应法     

脉冲激光沉积法制备的Ni1-xFexO稀磁半导体的结构和磁性研究

利用脉冲激光沉积方法制备出了具有室温铁磁性的Ni_1-xFe_xO(x=0.02,0.05)稀磁半导体.X射线衍射(XRD)结果表明Ni_1-xFe_xO的晶体结构为NaCl结构,并且在Fe含量较高的Ni_0.95Fe_0.05O中出现了少量的α-Fe₂O₃物相.X射线吸收近 关键词： 1-xFe_xO')" href="#">Ni_1-xFe_xO XANES 脉冲激光沉积方法     

Ti1－xCrxO2±δ体系的相关系、晶体结构和磁性能研究

采用溶胶凝胶法制备了Ti_1-xCr_xO_2±δ体系系列样品.利用扫描电子显微镜(SEM)，X射线光电子能谱(XPS)，粉末X射线衍射分析(XRD)方法研究了Ti_1-xCr_xO_2±δ系列样品的颗粒尺寸、形貌、组分化学态、相关系和固溶区范围；并利用超导量子干涉磁强计对样品的磁性能进行了研究.采用Rietveld结构精修的方法研究了Cr的不同掺杂量对TiO₂晶体结构的影响，研究表明，1000℃烧结的样品的固溶区范围是x=0—0.03，为金红石单相；随着Cr掺杂量的增加，金红石相晶胞参数规律性地减小；当x>0.03，为金红石相和CrO₂相两相共存.综合XRD和磁性测量结果，500℃烧结的样品的固溶区范围是x=0—0.02，为锐钛矿单相；随着Cr掺杂量的增加，锐钛矿相晶胞参数规律性地减小；当x≥0.04，为锐钛矿相和绿铬矿相(Cr₂O₃)两相共存.XPS实验结果表明，500℃和1000℃退火的样品中Cr都是以Cr⁺³和Cr⁺⁶两种化学态存在，1000℃烧结的样品中可能有更多的Cr³⁺转化为Cr⁶⁺.根据M-H和M-T曲线的测试结果发现，本文500℃烧结的Ti_1-xCr_xO_2±δ体系样品当x=0—0.02时，为室温铁磁性.当x≥0.04时，由铁磁相和顺磁相所组成，在低温下有较强的铁磁性；室温下主要是顺磁相，铁磁相只占据很小的体积分数. 关键词： 1-xCr_xO_2±δ体系')" href="#">Ti_1-xCr_xO_2±δ体系 相关系 固溶区 磁性能     

La0.1Bi0.9-xEuxFeO3化合物的结构与性能研究

利用固相反应烧结技术制备La_0.1Bi_0.9-xEu_xFeO₃系列化合物. 利用X射线粉末衍射进行物相鉴定和结构分析,确定了材料的相关系：x≤0.05,材料为R3c结构相;0.08≤x≤0.12,材料为赝R3c结构相;x≥0.15是Pbnm相,其中0.15≤x≤0.20区域Pbnm相存在畸变. 磁测量结果表明,材料具有弱铁磁性,对于x≤0.20材料,磁矩在x=0.12成分存在极值. 利用阻抗分析仪测量了室温介电常数随成分的变化关系.讨论了材料的结构与弱铁磁性和室温介电常数间的关系. 关键词： 0.1Bi_0.9-xEu_xFeO₃')" href="#">La_0.1Bi_0.9-xEu_xFeO₃ X射线衍射 磁性 介电常数     

MnxGe1－x稀磁半导体薄膜的结构研究

利用X 射线衍射(XRD)和X射线吸收精细结构(XAFS)方法研究了磁控共溅射方法制备的Mn_xGe_1-x薄膜样品的结构随掺杂磁性原子Mn含量的变化规律.XRD结果表明，在Mn的含量较低(7.0%)的Mn_0.07Ge_0.93样品中，只能观察到对应于多晶Ge的XRD衍射峰，而对Mn含量较高(25.0%, 36.0%)的Mn_0.25Ge_0.75和Mn关键词： 磁控溅射 XRD XAFS xGe_1-x稀磁半导体薄膜')" href="#">Mn_xGe_1-x稀磁半导体薄膜     

Mn掺杂ZnO稀磁半导体材料的制备和磁性研究

采用共沉淀方法制备了名义组分为Zn_1-xMn_xO(x=0.001,0.005,0.007,0.01)的Mn掺杂的ZnO基稀磁半导体材料,并研究了在大气气氛下经过不同温度退火后样品的结构和磁性的变化.结果表明：样品在600℃的大气条件下退火后, 仍为单一的六方纤锌矿结构的ZnO颗粒材料;当样品经过800℃退火后,Mn掺杂量为0.007,0.01的样品中除了ZnO纤锌矿结构外还观察到ZnMnO₃第二相的存在.磁性测量表明,大气条件下600℃退火后的样品,呈现出室温铁磁性;而800℃退火后的样品,其室温铁磁性显著减弱,并表现为明显的顺磁性.结合对样品的光致发光谱的分析,认为合成样品的室温铁磁性是由于Mn离子对ZnO中的Zn离子的替代形成的. 关键词： ZnO 掺杂 稀磁半导体 铁磁性     

赝二元固溶体TbGa1-xGex(0≤x≤0.4)的结构与磁性

采用电弧熔炼法在高纯氩气保护下合成了一系列TbGa_1-xGe_x(0≤x≤0.4)样品. X射线粉末衍射数据表明,样品均为正交晶系的CrB型结构,空间群为Cmcm. TbGa_1-xGe_x化合物的晶格常数随Ge含量的增加而线性减小,TbGa和TbGe赝二元系在0≤x≤0.4范围内形成固溶体. 化合物的顺磁居里温度以及有效磁矩由热磁测量结果确定. 相变温度由交流磁化率的测量获得. 随Ge含量的增加,化合物的相变温度单调下降. 变温X射线粉末衍射实验表明,x=0.2和0.3的样品在110—273K范围内无结构相变. 关键词： TbGa-TbGe 赝二元系 CrB结构 居里温度 磁化强度     

哈斯勒合金Ni-Co-Mn-Sn的马氏体相变及其磁热效应研究

通过结构和磁性测量,研究了四元哈斯勒合金Ni_50-xCo_xMn₃₈Sn₁₂（x=1, 2, 4, 6, 8）的晶体结构和相变特征.结果表明,Co原子的掺杂不但没有影响三元哈斯勒合金Ni-Mn-Sn的原有结构,而且还增强了样品在奥氏体相的铁磁交换作用.此外,通过Maxwell方程计算了其中三种成分样品（x= 2, 4, 6）的磁熵变ΔS_{M关键词： 哈斯勒合金 Ni-Co-Mn-Sn 马氏体相变 磁热效应}     

多晶Mn1-xCux(0.1≤x≤0.3)合金的磁诱发应变

采用X射线衍射分析、显微形貌观察、差示扫描量热法、标准电阻应变计法等实验方法,研究了室温下多晶Mn_1-xCu_x(0.1≤x≤0.3,原子分数)合金在低磁场中的磁诱发应变性能.结果表明,Mn_1-xCu_x合金经过长时间的固溶处理,在冷却过程中会出现fcc(γ)→fct(γ’)马氏体相变,形成(γ+γ 关键词： 磁诱发应变 MnCu合金 马氏体相变     

Properties of Co/Ni codoped ZnO based nanocrystalline DMS

Nanoparticles of Co and Ni codoped zinc oxide, Zn_0.9Co_0.1−xNi_xO (x=0.0, 0.03, 0.06 and 0.09), diluted magnetic semiconductors (DMSs) are synthesized by the sol-gel method at annealing temperature of 500 °C. X-ray diffraction (XRD) patterns confirm the single phase character of the samples with x=0.0 and 0.03. However, minor NiO secondary phase is detected in the samples with x=0.06 and 0.09. All of them possess the hexagonal wurtzite structure. There is no significant change in the lattice parameters due to variation of doping concentration. The average particle size is found to be 19.31-25.71 nm. FTIR and UV-vis spectroscopic results confirm the incorporation of the dopants into the ZnO lattice structure. Magnetization data reveal the presence of room temperature ferromagnetism (RTFM). The XRD patterns rule out the formation of secondary phase of either metallic Co cluster or CoO in the samples. Nevertheless, the secondary phases are a concern in any DMS system as a source of spurious magnetic signals. Therefore, we carried out the XPS studies from which the oxidation states of Co and Ni are found to be Co²⁺ and Ni²⁺, respectively. Moreover, XPS O 1s spectra show evidence of the presence of the oxygen vacancy in the ZnO matrix.     

Gd,Co共掺杂对BiFeO3陶瓷电输运和铁磁特性的影响

采用快速液相烧结法制备BiFeO₃和Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)陶瓷样品,研究Gd, Co共掺杂对BiFeO₃微观结构, 介电性能和铁磁性的影响. X射线衍射谱表明:所有样品的主衍射峰与纯相BiFeO₃相符合且 具有良好的晶体结构,随着Co³⁺掺杂量x的增大, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品的主衍射峰(104)与(110)逐渐相互重叠, 当x大于0.1时, 样品呈现正方晶系结构; J-V特性显示Gd³⁺, Co³⁺共掺杂有效地降低BiFeO₃陶瓷的漏导电流,其降低幅度为1-2个数量级; 当f=10³ Hz时, Bi_0.95Gd_0.05Fe_0.8Co_0.2O₃的介电常数是BiFeO₃的6倍, 而Bi_0.95Gd_0.05Fe_0.95Co_0.05O₃和 Bi_0.95Gd_0.05Fe_0.85Co_0.15O₃样品的介电损耗最小,均为0.01.室温下, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品磁性与BiFeO₃相比显著增强. 在磁场为30 kOe的作用下,Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)的剩余磁化强度M_r分别是BiFeO₃的34, 60, 105, 103, 180倍.样品磁性增强的主要原因是Gd, Co掺杂使BiFeO₃的晶格结构发生变化导致BiFeO₃自身储存的磁性能被释放, Gd³⁺的4f电子与Fe³⁺或Co³⁺的3d电子自旋相互作用及样品中存在局域的 Fe-O-Co磁耦合三者共同作用的结果.     

Co掺杂Bi5Ti3FeO15多铁陶瓷的磁电性能

采用了传统的固相烧结工艺制备出Bi₅Fe_1-xCo _{x Ti3O15(BFCT-x,x=0.0—0.6)多铁陶瓷样品,研究了Co掺杂对Bi5FeTi3O15(BFTO)微观结构、铁电和磁性能的影响.X射线衍射谱显示样品均已形成四层铋系层状钙钛矿相,且随着掺杂量的增加发生了结构变化.拉曼光谱进一步证实掺入的Co占据了< 关键词： 固相烧结 多铁陶瓷 剩余磁化 剩余极化}     

Room temperature ferromagnetism in Ni-doped ZnO films

Zn_1−xNi_xO (x = 0.02, 0.03, 0.04, 0.05, 0.07) films were prepared using magnetron sputtering. X-ray diffraction indicates that all samples have a wurtzite structure with c-axis orientation. X-ray photoelectron spectroscopy results reveal that the Ni ion is in a +2 charge state in these films. Magnetization measurements indicate that all samples have room temperature ferromagnetism. In order to elucidate the origin of the ferromagnetism, Zn_0.97Ni_0.03O films were grown under different atmospheric ratios of argon to oxygen. The results show that as the fraction of oxygen in the atmosphere decreases, both the saturation magnetization and the number of oxygen vacancies increase, confirming that the ferromagnetism is correlated with the oxygen vacancy level.     

Study of Sm-doped ZnO samples sintered in a nitrogen atmosphere and deposited on n-Si(1 0 0) by evaporation technique

The samarium doping zinc oxide (Zn_1-xSm_xO) with (x=0.0, 0.04, 0.05 and 0.17) polycrystalline thin films have been deposited on n-Si(1 0 0) substrate using thermal evaporation technique. Ceramic targets for deposition were prepared by the standard solid-state reaction method and sintered in nitrogen atmospheres. X-ray diffraction and scanning electron microscopy analyses show that the bulk and films features reveal wurtzite crystal structure with a preferential (1 0 1) crystallographic orientation and grows as hexagonal shape grains. According to the results of the Hall effect measurements, all the films show p-type conductivity, possibly a result of nitrogen incorporation into the Sm-doped ZnO samples. Magnetic measurements show that ferromagnetic behavior depends on the Sm³⁺ concentration. For a film with lower Sm₂O₃ contents (x=0.04), a phenomenon of paramagnetism has been observed. While, with further increase of Sm³⁺ contents (x=0.05) the ferromagnetic behavior has been observed at room temperature. However, at higher doping content of Sm³⁺, the ferromagnetic behavior was suppressed. The decrease of ferromagnetism with increasing doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Zn_1-xSm_xO films.     

Room-temperature ferromagnetism in Zn1−xMnxO

In view of recent controversies on above room-temperature ferromagnetism (RTFM) in transition-metal-doped ZnO, the present paper aims to shed some light on the origin of ferromagnetism by investigating annealing effects on structure and magnetism for polycrystalline Zn_1−xMn_xO powder samples prepared by solid-state reaction method and annealed in air at different temperatures. Magnetic measurements indicate that the samples are ferromagnetic at room temperature (RTFM). Room temperature ferromagnetism has been observed in the sample annealed at a low temperature of 500 °C with a saturated magnetization (M_s) of 0.159 emu/g and a coercive force of 89 Oe. A reduction in RTFM is clearly observed in the sample annealed at 600 °C. Furthermore, the saturation magnetic moment decreases with an increase in grain size, suggesting that ferromagnetism is due to defects and/or oxygen vacancy confined to the surface of the grains. The experimental results indicate that the ferromagnetism observed in Zn_1−xMn_xO samples is intrinsic rather than associated with secondary phases.     

X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics

ABSTRACT

The crystal structure modifications of BaTiO₃ induced by cobalt doping were studied. The polycrystalline (1 ? x)BaTiO₃ + xCo₂O₃ samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO₃. It was indicated that substitution of Co for the Ti sites in the (1 ? x)BaTiO₃ + xCo₂O₃ series led to decrease of tetragonality (c/a) of the BaTiO₃ perovskite structure. This effect almost vanished in the (1 ? x)BaTiO₃ + xCo₂O₃ samples with nominal Co content higher than ～1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co₂TiO₄ has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 ? x)BaTiO₃ + xCo₂O₃ series is estimated as x = 0.75 wt.%.