Co掺杂的ZnO室温铁磁半导体材料制备与磁性和光学特性研究

采用溶胶-凝胶法制备出具有室温铁磁性的Co掺杂的ZnO稀磁半导体材料. 通过对样品的结构、磁性和发光特性的研究发现,样品具有室温铁磁性,并发现其铁磁性源于磁性离子对ZnO中Zn离子的取代. 对不同温度制备的样品的磁性以及其发光特性的变化研究发现,样品的铁磁性与样品中锌间隙位（Zn_i）缺陷的密度有关. 关键词： ZnO 稀磁半导体 铁磁性     

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     

Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

溶胶凝胶合成锰掺杂ZnO的室温磁性行为

通过溶胶凝胶自燃法合成锰掺杂氧化锌纳米晶体, 研究了Mn掺杂ZnO稀磁半导体(简称DMS)的性质．X射线衍射光谱表明,锰掺杂氧化锌保留纤锌矿型状氧化锌六角晶体结构．采用能量色散X射线能谱和扫描电子显微镜分别对成分和形态进行研究．温度依赖的电阻率显示了DMS的半导体材料行为．振动样品磁强计测定的室温磁性行为,揭示了锰掺杂氧化锌的铁磁性和反磁性特性.     

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     

脉冲磁场下水热法制备Cr掺杂ZnO稀磁 半导体晶体

本文以ZnCl₂, CrCl₃. 6H₂O和氨水缓冲溶液为原料, 在4T脉冲磁场下水热法制备了Cr掺杂ZnO稀磁半导体晶体, 通过X射线衍射分析、扫描电子显微镜观察及采用振动样品磁强计进行磁性分析等, 探讨了脉冲磁场对其微观结构及磁性能的影响. 结果表明: Cr掺杂ZnO稀磁半导体晶体仍保持ZnO的六方纤锌矿结构, 脉冲磁场具有促进晶粒生长及取向排列的作用, 4T脉冲磁场条件下合成的Cr掺杂ZnO稀磁半导体具有良好的室温铁磁性, 其饱和磁化强度(M_s)为0.068 emu/g, 而无脉冲磁场情况下制备的样品室温下呈顺磁性, 并且, 脉冲磁场下制备将稀磁半导体的居里温度提高了16 K.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

共沉淀法制备Co掺杂ZnO的室温铁磁性的研究

利用共沉淀法并在5vol.%H₂/Ar气流中于300 ℃退火3 h,制备了Zn_1-xCo_xO稀磁半导体. 扫描电子微探针分析表明,对Co的名义组分分别为0.05,0.10,0.15的样品,其实际组分分别为x＝0.054, 0.100和0.159. X射线衍射表明, 主相为纤锌矿结构, x=0.100和 0.159的样品中含有CoO杂相. X射线光电子谱显示出Co有３种状态: 替代进入Z 关键词： 稀磁半导体 ZnO 共沉淀法 磁性来源     

高压处理对稀磁半导体Zn_(1-x)Mn_xO磁性的影响

用固相反应法制备出过渡金属Mn掺杂的ZnO系列样品,并对其进行了高压处理.高压处理后的样品,通过扫描电子显微镜和X射线衍射仪进行了微观结构的表征分析.通过磁性能的测量,初步研究了压力对Mn掺杂ZnO稀磁半导体磁性能的影响.结果表明:适当的高压处理可以有效增强材料的室温铁磁性,但当压力超过一定值后,压力会使材料的磁性能下降.     

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Zn1-zCoxO(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-xCoxO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Zn1-xCoxO稀磁半导体.通过对X射线吸收近边结构谱的分析,确定Zn1-xCoxO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Zn1-xCoxO产生室温铁磁性的主要原因.     

Ferromagnetism of MnxLiyZn1−x−yO films

We had prepared Mn-doped ZnO and Li, Mn codoped-ZnO films with different concentrations using spin coating method. Crystal structure and magnetic measurements demonstrate that the impurity phases (ZnMnO₃) are not contributed to room temperature ferromagnetism and the ferromagnetism in Mn-doped ZnO film is intrinsic. Interesting, saturated magnetization decreases with Mn or Li concentration increase, showing that some antiferromagnetism exists in the samples with high Mn or Li concentration. In addition, Mn_0.05Zn_0.95O film annealed in vaccum shows larger ferromagnetism than the as-prepared sample and more oxygen vacancies induced by annealing in reducing atmosphere enhance ferromagnetism, which supports the bound magnetic polaron model on the origin of room temperature ferromagnetism.     

Effect of vanadium doping on structural, magnetic and optical properties of ZnO nanoparticles

V-doped ZnO nanoparticles were synthesized by heating metal acetates in organic solvent. All synthesized samples were annealed in air and reducing gas atmosphere at 600 °C for 8 h. The XRD patterns of both samples annealed in air and reducing atmosphere indicate that samples have polycrystalline wurtzite structure with increase in lattice constant with increase in V-doping. The particle sizes were calculated by using Scherrer's equation which lies in the range of 25-30 nm. The SEM images show that particles annealed in air and under reducing environment are spherical in nature. The EDX results reveal that samples contain V, Zn, and O contents only. The TPR results indicate that the system contains isolated VO_x, ZnO_x and bimetallic Zn: V (O_x) sites and indication of electronically excited bimetal sites. There is no signature of ferromagnetism in all samples annealed in air while room temperature ferromagnetism has been observed only under reducing atmosphere annealing. There is monotonically increase in saturation magnetization with V-doping concentration. UV-vis spectroscopy study shows that there is a linear increase in band gap energy with increase in V-doping, a direct evidence of change in magnetic properties due to V-doping and under reducing environment.     

Effect of thermal treatment on room-temperature ferromagnetism in Co-doped ZnO powders

The Co-doped ZnO powders were synthesized by sol-gel method, and treated at different temperatures (673-873 K) in the presence or absence of NH₃ atmosphere for 0.5 and 2 h, respectively. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) show that better crystal structure can cause larger ferromagnetism and the second phase (Co₃O₄) is the reason for saturation magnetization decrease of the sample sintered at higher temperature in air. XPS and nuclear magnetic resonance (NMR) prove the existence of Co²⁺ ions in the Zn_0.9Co_0.1O and the absence of Co clusters, indicating intrinsic ferromagnetism of the samples treated in air. However, strong ferromagnetism of the samples annealed in NH₃ is ascribed to cobalt nitride formed during annealing.     

Effect of annealing temperature on structure, magnetic properties and optical characteristics in Zn0.97Cr0.03O nanoparticles

The Cr-doped zinc oxide (Zn_0.97Cr_0.03O) nanoparticles were successfully synthesized by sol-gel method. The relationship between the annealing temperature (400 °C, 450 °C, 500 °C and 600 °C) and the structure, magnetic properties and the optical characteristics of the produced samples was studied. The results indicate that Cr (Cr³⁺) ions at least partially substitute Zn (Zn²⁺) ions successfully. Energy dispersive spectroscopy (EDS) measurement showed the existence of Cr ion in the Cr-doped ZnO. The samples sintered in air under the temperature of 450 °C had single wurtzite ZnO structure with prominent ferromagnetism at room temperature, while in samples sintered in air at 500 °C, a second phase-ZnCr₂O₄ was observed and the samples were not saturated in the field of 10000 Oe. This indicated that they were mixtures of ferromagnetic materials and paramagnetic materials. Compared with the results of the photoluminescence (PL) spectra, it was reasonably concluded that the ferromagnetism observed in the studied samples was originated from the doping of Cr in the lattice of ZnO crystallites.     

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.     

Growth,electronic and magnetic properties of doped ZnO epitaxial and nanocrystalline films

We have used oxygen plasma assisted metal organic chemical vapor deposition along with wet chemical synthesis and spin coating to prepare Co_xZn_1-xO and Mn_xZn_1-xO epitaxial and nanoparticle films. Co(II) and Mn(II) substitute for Zn(II) in the wurtzite lattice in materials synthesized by both methods. Room-temperature ferromagnetism in epitaxial Co:ZnO films can be reversibly activated by diffusing in Zn, which occupies interstitial sites and makes the material n-type. O-capped Co:ZnO nanoparticles, which are paramagnetic as grown, become ferromagnetic upon being spin coated in air at elevated temperature. Likewise, spin-coated N-capped Mn:ZnO nanoparticle films also exhibit room-temperature ferromagnetism. However, the inverse systems, N-capped Co:ZnO and O-capped Mn:ZnO, are entirely paramagnetic when spin coated into films in the same way. Analysis of optical absorption spectra reveals that the resonances Co(I)↔Co(II)+e^- _CB and Mn(III)↔Mn(II)+h⁺ _VB are energetically favorable, consistent with strong hybridization of Co (Mn) with the conduction (valence) band of ZnO. In contrast, the resonances Mn(I)↔Mn(II)+e^- _CB and Co(III)↔Co(II)+h⁺ _VB are not energetically favorable. These results strongly suggest that the observed ferromagnetism in Co:ZnO (Mn:ZnO) is mediated by electrons (holes). PACS 75.50.Pp     

Structural, optical and magnetic properties of (ZnO)1−x(MnO2)x thin films deposited at room temperature

The structural, magnetic and optical properties of (ZnO)_1−x(MnO₂)_x (with x = 0.03 and 0.05) thin films deposited by pulsed laser deposition (PLD) were studied. The pellets used as target, sintered at different temperatures ranging from 500 °C to 900 °C, were prepared by conventional solid state method using ZnO and MnO₂ powders. The observation of non-monotonic shift in peak position of most preferred (1 0 1) ZnO diffraction plane in XRD spectra of pellets confirmed the substitution of Mn ions in ZnO lattice of the sintered targets. The as-deposited thin film samples are found to be polycrystalline with the preferred orientation mostly along (1 1 0) diffraction plane. The UV-vis spectroscopy of the thin films revealed that the energy band gap exhibit blue shift with increasing Mn content which could be attributed to Burstein-Moss shift caused by Mn doping of the ZnO. The deposited thin films exhibit room temperature ferromagnetism having effective magnetic moment per Mn atom in the range of 0.9-1.4μ_B for both compositions.     

Influence of annealing temperature on structural, optical and magnetic properties of Zn0.95Cu0.02Cr0.03O powders

Zn_0.95Cu_0.02Cr_0.03O powders have been synthesized by the sol-gel method and sintered in argon atmosphere under different temperatures. The structural, optical and magnetic properties of the powders were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and vibrating sample magnetometer (VSM). The XRD results demonstrated that Cr and Cu ions are incorporated into ZnO successfully when annealing temperatures were 600 and 700 °C. But when the samples were annealed at 500 °C, the crystallinity of the samples was not very good. However, when the annealing temperature was increased to 800 °C, the secondary phase of Cu and ZnCr₂O₄ appeared in the samples. The PL spectra revealed that the position of the ultraviolet (UV) emission peak of the samples showed a blue shift and the green emission peak enhanced significantly with the annealing temperature increasing from 600 to 700 °C. Magnetic measurements indicated that the room temperature ferromagnetism of Zn_0.95Cu_0.02Cr_0.03O was intrinsic in nature. In addition, the saturation magnetization (Ms) increased from 0.0078 to 0.0088 emu/g with the annealing temperature increased from 600 to 700 °C.