Fe掺杂量和退火氛围对TiO2薄膜晶体结构和磁性能的影响

采用直流磁控溅射方法在玻璃基片上制备了不同Fe掺杂量的TiO2薄膜,并对薄膜分别在空气和真空氛围下500℃进行30min退火处理。研究了Fe掺杂量和退火氛围对TiO2薄膜的结晶状态、表面形貌和磁性能的影响。结果表明,真空中500℃下退火的Fe掺杂的TiO2薄膜表现为非晶态结构,没有观察到室温铁磁性能的出现,而空气中500℃退火的样品显示出良好的结晶状态,且所有掺杂的样品均显示出室温铁磁性,并且随着Fe掺杂量的增加,TiO2薄膜的晶体结构逐渐由锐钛矿相向金红石相转变。     

氢气热处理对纳米TiO2可见光吸收性能的影响

在H2还原气氛中对纳米TiO2粉末进行热处理改性研究发现,氢气热处理改性后的样品中存在氧空位缺陷,使纳米TiO2的光吸收阈值红移.在试验条件下,最佳的处理温度在700℃左右,该温度下,锐钛矿型、金红石型和混晶型纳米TiO2的光吸收阈值分别为450、490和500nm.以甲基橙溶液为降解模型实验结果表明,改性处理后的样品在可见光下具有光催化活性.     

质子辐照对Yb掺杂ZnO稀磁半导体薄膜缺陷与磁性的影响

采用电感耦合等离子体增强物理气相沉积法制备了Yb掺杂ZnO薄膜, 并采用不同剂量质子对薄膜进行了辐照实验, 重点采用X射线衍射、光电子能谱、正电子湮灭图谱和磁测量系统对Zn_0.985Yb_0.015O薄膜的缺陷和磁性能进行了研究。磁性测试结果表明: Zn_0.985Yb_0.015O薄膜经质子辐照后其饱和磁化强度随辐照剂量的增加逐渐增大, 当辐照剂量为6 × 10¹⁵ ions/cm²时, 其饱和磁化强度达到最大, 随着辐照剂量的进一步增加, 其饱和磁化强度反而变小。正电子湮灭图谱结果显示薄膜中主要存在锌空位相关的缺陷, 并且锌空位相关的缺陷随辐照剂量的变化与饱和磁化强度随辐照剂量的变化相一致。本研究从实验上揭示了在含有各种缺陷的Yb掺杂ZnO薄膜中, 锌空位缺陷是影响质子辐照Zn_0.985Yb_0.015O薄膜磁性的主要原因。     

锰掺杂氧化铜稀磁半导体薄膜的微结构和磁性

采用射频磁控溅射制备Mn掺杂CuO薄膜样品。X射线衍射结果说明薄膜样品为单相结构且沿（111）取向生长。通过样品的XRD精修得到样品的结构和晶格参数,掺杂后薄膜晶体结构有微小畸变。薄膜的高分辨透射电镜研究证明了对结构和晶粒大小等的精修结果,且同时说明Mn以替代Cu的形式掺入了CuO晶格中。通过对样品M1T曲线的分析,得到样品的居里温度为96．5K,近邻Mn离子之间的耦合为铁磁性,并由居里外斯拟合得到Mn离子的有效磁矩为3．1μa。这说明磁性不是来自于团聚的Mn原子或铜锰的其它氧化物,而很可能来自于替位的锰离子所形成的Mn-O-Cu-O-Mn之间的铁磁性耦合。     

水热法制备的Ti1-xCoxO2稀磁半导体特性

采用水热法制备出Ti1-xCoxO2(x=0～0.10)稀磁半导体材料,并对其形貌、结构及磁性能进行表征.X射线衍射分析结果表明,纯TiO2样品为锐钛矿相,掺杂Co离子后样品中出现金红石相,当掺杂浓度到0.10时样品中出现Co3O4的衍射峰.透射电镜和X射线能量色散谱测试结果表明,样品形貌规整,平均粒径约为20nm,并且证实样品中含有Co元素.利用振动样品磁强计对其磁性进行测量,结果表明样品在室温条件下存在铁磁性.     

Mn掺杂ZnO稀磁半导体的化学合成及磁性研究

采用化学方法制备了名义组分为Zn0.993Mn0.007O的Mn掺杂ZnO稀磁半导体材料,并研究了退火温度(Ts＝400,600,800℃)对其结构和磁性的影响.结果表明:在退火温度低于600℃条件下,合成的样品为单一纤锌矿结构的ZnO颗粒材料;当退火温度为800℃时,合成的样品中除了纤锌矿结构ZnO外还观察到ZnMnO3第二相的存在.磁性研究表明:经过600℃退火后的样品,其室温铁磁性最强,而经过800℃退火后的样品,其铁磁性几乎消失,并表现为增强的顺磁性.结合对样品的Raman光谱和紫外-可见吸收光谱的分析,表明Mn元素进入了ZnO晶格中并替代了ZnO中的Zn离子. 样品的室温铁磁性是源于(Zn,Mn)O的本征特性,并排除了样品中第二相导致其具有室温铁磁性的可能性.     

磁控溅射法制备Zn_(1-x)Co_xO薄膜的磁性能

采用磁控溅射工艺,在玻璃基片上制备了Zn1-xCoxO(x=0.02~0.15)稀磁半导体薄膜。采用X-射线衍射(XRD)、X射线光电子能谱(XPS)、原子力显微镜(AFM)、振动样品磁强计(VSM)研究了薄膜的相结构、化学成分及价态、表面形貌和磁性能。结果表明,本实验条件下,薄膜不存在Co及Co的氧化物相,薄膜中Zn的化学价为+2,Co则以+2和+4价的形式存在;薄膜晶体结构为c轴取向生长的六方纤锌矿结构;薄膜表面平整致密。在温度为300 K时,Zn0.9Co0.1O薄膜呈铁磁效应,在M-H曲线中观测到明显的磁滞回线特征。     

Mn注入 n型 Ge单晶的特性研究

采用离子能量为 100keV,剂量为 3× 1016cm- 2的离子注入技术,室温下往 n型 Ge( 111)单晶 衬底注入 Mn+离子,注入后的样品进行 400℃热处理.利用 X-射线衍射法 (XRD)和原子力显微 镜( AFM)对注入后的样品进行了结构和形貌分析, 俄歇电子能谱法 (AES)进行了组分分析,交变 梯度样品磁强计( AGM)进行了室温磁性测量.结果表明原位注入样品的结构是非晶的,热处理后 发生晶化现象.没有在样品中观察到新相形成. Mn离子较深的注入进 Ge衬底,在 120 nm处 Mn原子百分比浓度达到最高为 8%.热处理后的样品表现出了室温铁磁特性.     

ZnO基稀磁半导体磁性机理研究进展

稀磁半导体是指在非磁性化合物半导体中通过掺杂引入部分磁性离子所形成的一类新型功能材料.目前,稀磁半导体的磁性来源和机理一直是该领域的研究热点,掺杂的磁性离子通过怎样的交换方式实现铁磁性一直存有争议.本文对近几年来ZnO基稀磁半导体磁性机理研究进展作一综述,着重阐述了代表性的RRKY理论、平均场理论、双交换理论和磁极子理论,对实验和理论方面的热点和存在问题作一评价,对磁性理论的研究提出了新思路.     

(Ga,Mn)As稀磁半导体的杂质动力学模拟研究

结合第一性原理计算和动力学蒙特卡罗模拟研究了稀磁半导体(Ga,Mn)As中Mn杂质的沉积动力学规律。利用第一性原理计算和爬坡弹性带方法计算了Mn杂质的跃迁势垒和结合能,并把这些能量作为动力学蒙特卡罗模拟(Ga,Mn)As微观结构演化的输入数据。结果表明在外延生长退火下长时间的微观结构演化的背后机制是Ga空位调节Mn原子在Ga子晶格上进行扩散。这种扩散会导致Mn原子的聚集,进而降低了居里温度。此外,随着退火温度的升高Mn团簇聚集的速率也更快。在高温退火下容易导致相分离。     

Effect of GaAs Intermediary Layer Thickness on the Properties of (Ga,Mn)As Tri-Layer Structures

We have investigated the magnetic properties, current–voltage characteristics, and tunnel magnetoresistance of (Ga,Mn)As/GaAs/(Ga,Mn)As tri-layers having different thickness of the intermediary GaAs layer (1–7 nm). When the thickness of GaAs layer is less than 6 nm, the two (Ga,Mn)As layers couples ferromagnetically. For the tri-layers with thicker GaAs, the GaAs acts as an effective barrier for the carrier transport and decouples the two (Ga,Mn)As layers, which results in tunnel magnetoresistance ratio as high as 100% at 5 K.     

Influence of preparation condition and doping concentration of Fe-doped ZnO thin films: Oxygen-vacancy related room temperature ferromagnetism

Fe-doped and Fe-Ga co-doped ZnO diluted magnetic semiconductor thin films on quartz substrate were studied. Rapid annealing enhanced the ferromagnetism (FM) of the films grown in Ar/O₂. All the films grown in Ar are n-type and the carrier concentration could increase significantly when Ga is doped. The state of Fe in the films was investigated exhibiting Fe³⁺. Magnetic measurements revealed that room temperature ferromagnetism in the films were doping concentration dependent and would enhance slightly with Ga doping. The origin of the observed FM is interpreted by the overlapping of polarons mediated through oxygen vacancy based on the bound magnetic polaron model.     

Study of ferromagnetism in Mn-doped ZnO whisker arrays

Vertically aligned Mn-ZnO whiskers were grown on sapphire substrate by a thermal chemical vapour deposition method. X-ray diffraction measurements indicate that samples are high-quality single crystals and c-axis oriented. Raman and XPS analyses revealed that Mn was incorporated into the ZnO lattice. Room temperature T _c ferromagnetism was observed. These Mn-ZnO whiskers may find their potential applications in spintronic field.     

Spin Carrier Exchange Interactions in (Ga,Mn)N and (Zn,Co)O Wide Band Gap Diluted Magnetic Semiconductor Epilayers

(Ga,Mn)N and (Zn,Co)O wide band gap diluted magnetic semiconductor epilayers have been investigated by magneto-optical spectroscopy. In both cases, absorption bands observed below the energy gap allow us to study the nature of the valence and spin state of the incorporated magnetic element. Exchange interactions between magnetic ions and carriers can be observed by analyzing the magnetic circular dichroism in transmission or the exciton Zeeman splitting in reflection for (Zn,Co)O. A first estimation of the exchange integrals can be given for both materials.     

纳米Zn1-xFexSe薄膜的制备和结构研究

采用双源热蒸发方法制备了纳米 Zn1-xFexSe稀释磁性半导体薄膜,根据 X 射线衍射谱和Raman散射谱研究了薄膜的晶体结构和声子谱特征。结果表明:Zn1-xFexSe薄膜中纳米晶粒的晶格常数随Fe含量增加而增大;通过 Raman 散射光谱观察到明显的声子限域效应,与 ZnSe体材料相比,Zn1-xFexSe薄膜同光学声子模对应的 Raman 散射峰表现出宽化和红移;纳米晶粒的晶格膨胀导致 Raman散射峰红移随Fe含量增多而相应加大。     

La掺杂对Sr2Bi4Ti5O18铁电陶瓷性能的影响

利用传统的固相烧结工艺制备了Sr2LaxBi1-xTi5O18(x=0．00、0．05、0．1、0．25、0．5、0．75、1．00)陶瓷样品。用X射线衍射对其微结构进行了分析．并测量了其铁电、介电性能。X射线衍射结果表明La掺杂对Sr2Bi4TixO18的晶体结构几乎没有影响。样品的铁电、介电结果表明。随着La掺杂量的增加，样品的剩余极化(2Pr)和矫颈场(Ec)逐渐减小。这是由于离子半径较大的La取代类钙钛矿层A位Bi离子。使得样品晶格畸变变小，从而导致2Pr降低。晶格畸变的减小也使得沿着外电场方向氧八面体中的阳离子更易运动。导致Ec减小。样品的相变温度L随着La含量的增加而降低。这也与样品晶格畸变有关。     

基于从头算法的TM金属共掺杂的ZnO基稀磁半导体的磁性研究(英文)

本文采用从头计算的方法研究了基于过渡性金属共掺杂Ⅱ-Ⅵ族稀释半导体的磁性和电子结构.并系统的研究了氧化锌基的稀释半导体铁磁态的稳定性和对其材料设计.在所有的共掺杂体系中,发现(Mn,Co),(Co,Ni)和(Mn,Ni)共掺杂体系是铁磁态的,而(Fe,Ni)共掺杂体系是自旋玻璃态.另一方面,Fe-,Co-和Ni掺杂ZnO基系统的稳态是铁磁态.同时,本文研究了ZnO基稀释半导体的载流子传导铁磁性,计算分析了电子态密度,铁磁态的稳定性.结合双交换和超交换理论解释共掺杂稀释半导体的磁性机理.     

Influence of Codoping on the Magnetoresistance of Paramagnetic (Ga,Mn)As

We studied the correlation between magnetoresistance (MR) effects and the type of conducti- vity in paramagnetic Ga_1–x Mn _x As with x < 0.5%. Series of samples of (Ga,Mn)As with different codoping levels of Te have been prepared by metal-organic vapor-phase epitaxy (MOVPE). With increasing Mn-content from doping levels to x = 0.5% in paramagnetic Ga_1–x Mn _x As, the MR at 1.6 K changes continuously from positive to strongly negative. This manifests the complex interplay between p–d exchange induced valence band splitting and the metal–insulator transition. Codoping with Te leads eventually to a dominant conduction band transport. It is characterized by a small negative contribution at low magnetic fields to the parabolic MR similar to that found in highly n-doped diamagnetic semiconductors. It shows that the Mn-induced conduction band splitting is much smaller than the valence band splitting, i.e., |N₀| |N₀|.     

The impact of annealing temperature on the structural and magnetization properties of Sm implanted GaN films

The impact of the annealing temperature on the structural and magnetic characteristics of GaN:Sm films fabricated by implantation method have been investigated in this paper. High-resolution X-ray diffraction (HRXRD) results indicate that the concentration of defects in samples decreases with increasing annealing temperature. Superconducting quantum interference device (SQUID) results show that all samples exhibit room-temperature ferromagnetic properties and colossal magnetic effect. Moreover, the average saturation magnetization per Sm atom (Ms/Sm) of samples decreases sharply with increasing annealing temperature. The strong colossal magnetic effect (496.6 μ_B/Sm) of samples annealed at 700 °C may have close relation with its high concentration defects.