Mo低掺杂La_(0.67)Sr_(0.33)MnO_3的磁电特性及室温磁电阻增强(英文)

采用固相反应法成功制备了Mo低掺杂La0.67Sr0.33Mn1-xMoxOc(x=0,0.02)单相多晶样品,系统研究了样品的磁性、电输运特性和磁电阻效应.发现Mo低掺杂对La0.67Sr0.33MnO3 的居里温度影响很小,但在La0.67Sr0.33MnO3铁磁基态背景下诱导出团簇自旋玻璃态行为.在低温区(0.1相似文献   

沉积氧压对La0.8Sr0.2MnO3/0.7wt%Nb:SrTiO3异质结的整流伏安特性及输运性的调控

采用脉冲激光沉积法在(100)0.7wt%Nb:SrTiO3(NSTO)衬底上制备了La0.8Sr0.2MnO3(LSMO)/NSTO(100)异质结,仔细研究了原位沉积氧压和真空退火对LSMO/NSTO异质结的结构及其整流伏安特性的调控.X-射线线性扫描和原子力显微镜测量显示,低氧压制备的LSMO/NSTO(100)异质结具有良好的外延结构和平整的表面.电流-电压(I～V)曲线显示,沉积氧压为100mTorr的异质p～n结展现出极好的整流伏安特性;而氧压为240mTorr的异质p～n结平缓增加的电流可解释为异质p～n结在界面处晶格缺陷的增加.作为对比,沉积氧压调控的LSMO/SrTiO3(100)薄膜的输运性也被研究.电阻率结果显示,低氧压制备的LSMO薄膜,其电阻率的增加及金属-半导体转变温度Tp的降低归因于氧空位增加诱导的Mn4+离子减少及MnO6八面体的畸变.     

(110)取向La0.67Sr0.33MnO3-δ外延膜的结构和磁电阻效应研究

采用直流磁控溅射法在(110)LaAlO3单晶基片上制备了La0.67Sr0.33MnO3-δ外延膜,系统地研究了样品的结构以及基片温度、外磁场对磁电阻效应的影响.将LSMO/(110)系列样品与LSMO/(001)系列样品的电阻率对比之后,发现基片的不同取向对该系列样品的电输运性质有很大的影响.原因是在不同取向时,氧原子进入薄膜的几率不同,导致Mn+3/Mn+4的比率不同,使得晶格常数、Mn+3和Mn+4与O-2之间的相互作用和原子磁矩的取向发生了变化,从而引起了金属到半导体的转变温度Tp移向高温区域和电阻率明显下降.     

La5/8-xPr xCa3/8MnO3体系电输运特性的研究

对La5/8-xPrxCa3/8MnO3(x＝0,0.13,0.20,0.25)体系的电输运特性进行了系统研究.结果表明随着Pr含量的增大金属-绝缘转变温度(TMI)减小,在高于TMI的温度区域,该体系的电输运行为具有绝缘体特性,符合可变程跳跃模型;而在较低温度(50 K以下),其电阻率存在极小值现象,且随磁场的增大而逐渐受到抑制.对这种电阻率极小值现象从强电子-电子相互作用角度进行了分析讨论.     

LaNiO3-δ 薄膜中的氧缺位及其对金属输运行为的影响

钙钛矿结构 LaNiO3 因其高电导的金属性输运行为, 有望作为电极材料在今后的氧化物器件工艺中发挥重要作用. 为了细致认识氧缺位对其金属输运的影响, 本文采用溶胶凝胶法在氧气、 空气和真空等气氛下烧结获得具有不同缺氧量的 LaNiO3 -δ 薄膜, 并利用 Mn3 + 的还原性进一步调整其缺氧量δ . 对这些样品的电阻率温度关系测量结果表明, 缺氧量δ > 0. 1 后薄膜的高温电阻率开始超过 Mott-Ioffe-Regel 极限, 变成“坏金属”; 增大δ 至0.2, 薄膜的低温剩余电阻率大幅度上升, 说明氧空位分布无序性导致的载流子局域化有明显作用. 以上样品的金属输运都呈非费米液体行为. 继续增加氧缺位浓度, 样品电阻率在低温a30 K 以下呈绝缘体温度关系, 同时高温金属态转变为费米液体行为, 说明钙钛矿结构镍酸盐的金属-绝缘体转变与费米液体输运之间或存在关联性.     

(La_(1-x)Ce_x)_(2/3)Ca_(1/3)MnO_3体系的结构和输运性质研究

对Ce掺杂锰氧化物 (La1 -xCex) 2 3Ca1 3MnO3(x =0— 1.0 )多晶样品的结构和输运性质系统研究的结果 .实验表明 ,在低掺杂浓度下 ,样品呈现完整的正交钙钛矿结构 ;随掺杂浓度的增加 ,有少量CeO2 杂相出现 ,同时伴随有Ce3 和Ce4 离子两种价态的涨落和Mn2 Mn3 Mn4 混合价态的共存 ,Ce掺杂导致的体系无序度增加 ,使得绝缘体 -金属 (I M)和顺磁 -铁磁 (PM FM)转变温度向低温方向移动 .有趣的是 ,Ce掺杂样品的电阻率测量I M转变峰值温度TIM 较PM FM转变温度Tc 为高 ,其差值ΔT(=TIM -Tc)随Ce掺杂含量的增加而增加 ,最大差值ΔT达 5 0K .各样品的磁电阻则随温度的降低而增加 ,在Tc 附近MR达到最大值 ,且随Ce掺杂含量增加Tc 附近的MR最大值迅速增加 ,达到 10 4 %以上 ,表现出很强的庞磁电阻效应 .在x≥ 0 .7时 ,磁电阻效应则表现出反常减小 .整体上而言 ,各样品的磁特性与输运行为间有较强的关联 ,电输运特性可用双交换作用模型进行很好的解释 ,在高温区满足热激活模型 .最后 ,在Ce掺杂对Tc 和MR的影响机理方面进行了初步讨论 .     

La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3(0.0≤x≤0.15)中异常的CMR效应

我们研究了Mn位掺Cr体系La0 .67Ca0 .33Mn1-xCrxO3( 0 .0≤x≤ 0 .15)的磁性和磁电阻性质 ,发现Cr掺杂对居里温度Tc 影响不明显 ,但是导致了反常的电输运和磁电阻行为 ,随着Cr含量的增加 ,起始电阻率峰向低温移动 ,同时电阻率出现一个附加峰 .在磁场作用下 ,两个电阻率峰被强烈压缩 ,导致CMR效应中出现双峰 ,并且CMR效应的温区被极大地拓宽 ,从低温直到接近室温 .这个结果表明 :Mn位元素替代是调节CMR效应的有效方法 .     

La0.9Sr0.1MnO3薄膜中电流效应研究

用直流磁控溅射法在(100)LaAlO3衬底上制备了La0.9Sr0.1MnO3薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La0.9Sr0.1MnO3薄膜在281 K处发生金属绝缘体转变.电流在0.01-4 mA范围内,薄膜的峰值电阻率随电流增大而减小,在4 mA下获得了30.5%的峰值电阻率变化率,并从相分离图像给出了简单解释.     

晶界效应对钙钛矿La_(0.7)Ba_(0.3)MnO_3多晶材料的磁输运特性的影响(英文)

本文通过比较La0.7Ba0.3MnO3多晶和外延薄膜样品磁输运行为之间的差异,讨论了晶界对多晶样品输运特性的影响,并计算了晶界电阻率随温度和磁场的变化关系.与晶粒的本征电阻率相比,晶界的电阻率要大一个量级,并且其金属-绝缘转变温度低约50K.此外,在晶界中观察到了新奇的正磁阻效应.我们认为,晶界在其转变温度附近出现了相分离现象,并形成铁磁金属渗流通道.由于晶界的特殊构型,Ba掺杂锰氧化物材料中大的磁致伸缩效应对其输运行为影响很大,导致了晶界中正磁阻现象的出现.     

(1-x)La_(0.7)Ca_(0.3)MnO_3/xCoFe_2O_4复合体系的电子输运和磁电阻特性的研究

本文采用两步法制备了(1-x)La0.7Ca0.3MnO3/xCoFe2O4复合样品,对样品的电磁输运特性的测量表明,随着CFO含量的增加,复合样品电阻率增大,且出现双峰,而比饱和磁矩却先减小后增大;另外在样品中观察到了低温增强的磁电阻效应,这一低场磁电阻效应与颗粒晶界处传导电子所受到的自旋极化隧穿和散射有关.     

锰的硅化物薄膜在Si(100)-2×1表面生长的STM研究

锰的硅化物在微电子器件、自旋电子学器件等领域具有良好的应用前景, 了解锰的硅化物薄膜在硅表面的生长规律是其走向实际应用的关键步骤之一. 本文采用分子束外延方法在Si(100)-2× 1表面沉积了约4个原子层的锰薄膜, 并利用超高真空扫描隧道显微镜研究了该薄膜与硅衬底之间在250-750℃范围内的固相反应情况. 室温下沉积在硅衬底表面的锰原子与衬底不发生反应, 薄膜由无序的锰团簇构成; 当退火温度高于290℃时, 锰原子与衬底开始发生反应, 生成外形不规则的枝晶状锰硅化物和富锰的三维小岛; 325℃时, 衬底上开始形成平板状的MnSi小岛; 525℃时, 枝晶状锰硅化物完全消失, 出现平板状的MnSi_1.7大岛; 高于600℃时, 富锰的三维小岛和平板状的MnSi小岛全部消失, 仅剩下平板状的MnSi_1.7大岛. 这些结果说明退火温度决定了薄膜的形态和结构. 在大约600℃退火时岛的尺寸随着退火时间的延长而逐渐增大, 表明岛的生长遵从扩散限制的Ostwald熟化机理.     

Phase transformations in Mn/Fe(001) films: Structural and magnetic investigations

The solid-phase synthesis in epitaxial Mn/Fe(001) bilayer film systems with 24 at % of Mn has been shown to start at a temperature of 220°C with the formation of a γ-austenite lattice and the Mn and Fe films react completely under annealing to 600°C. In the sample cooling process after annealing below 220°C, the γ austenite undergoes a martensitic transformation to an oriented ∈(100) martensite. When the annealing temperature is increased above 600°C, Mn atoms migrate from the γ-lattice, which becomes unstable, and the film is partially again transformed to the epitaxial Fe(001) layer. The solid-phase synthesis in Mn/Fe(001) bilayer nanofilms and multilayers is assumingly determined by the inverse ε → γ martensitic transformation in the Mn-Fe system. The existence of a new low-temperature (～220°C) structure transition in the Mn-Fe system with a high iron content is assumed.     

Experimental evidence of coupling interaction between charge ordering and spin ordering

In order to experimentally probe into the complicated interaction between charge ordering and spin ordering in manganites,two sets of samples Nd0.5Sr0.5Mn1-xGaxO3(NSMGO) and Nd 0.5Sr0.5Mn1-y CryO3(NSMCO)(0.0 x,y 0.075),have been studied by means of electrical transport,magnetization,electron spin resonance and transmission electron microscopy analysis.By comparing the influence of Cr-doping and Ga-doping in the Nd0.5Sr0.5MnO3(NSMO) system,large difference between the evolution of charge ordering temperature T co in the Cr-doping and the Ga-doping cases is found.In the NSMCO system,the CE-type antiferromagnetic(AFM)/charge ordering(CO) phase disappears with only 2.5 percent Cr doping;but in the NSMGO system,the CE-type AFM/CO phase always exists.This phenomenon indicates that the charge ordering formation is dominated by the spin ordering.As a result,it is experimentally proved that there is strong coupling interaction between charge ordering and spin ordering in NSMO system.     

Fabrication of ferromagnetic (Ga,Mn)As by ion irradiation

Using Mn⁺ implantation following ion beam-induced epitaxial crystallization (IBIEC) annealing, high Curie temperature ferromagnetic (Ga,Mn)As thin film was fabricated. The crystalline quality of the Mn⁺ implanted layer was identified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). A clear ferromagnetic transition at T_c 253 K was observed by magnetization vs. temperature measurement. We infer that IBIEC treatment is a useful method not only for the low-temperature annealing of (Ga,Mn)As thin films but also for other dilute magnetic semiconductor (DMS) samples.     

高质量稀磁半导体(Ga,Mn)Sb单晶薄膜分子束外延生长

理论预言窄禁带稀磁半导体(Ga,Mn)Sb及其异质结构可能存在量子反常霍尔效应等新奇特性, 近年来受到了特别关注. 但是, 由于(Ga,Mn)Sb薄膜生长窗口窄, 纯相(Ga,Mn)Sb薄膜制备比较困难, 迄今关于这类材料的研究报道为数不多. 本文采用低温分子束外延的方法, 通过优化生长条件, 成功制备出厚度为10 nm, Mn含量在0.016至0.039之间的多组(Ga,Mn)Sb薄膜样品. 生长过程中反射式高能电子衍射原位监测和磁性测量都表明没有MnSb等杂相的偏析, 同时原子力显微镜图像表明其表面形貌平滑, 粗糙度小. 通过生长后退火处理, (Ga,Mn)Sb薄膜的最高居里温度达到30 K. 此外, 本文研究了霍尔电阻和薄膜电阻随磁场的变化关系, 在低温下观测到明显的反常霍尔效应.     

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.     

CoPt(FePt)-C纳米复合膜的结构与磁性

用磁过滤脉冲真空电弧沉积方法制备了CoPt(FePt) C纳米复合薄膜，并在不同温度下进行了退火处理，研究了薄膜中碳的含量以及退火温度对薄膜结构与磁性能的影响.制备态薄膜经过足够高的温度退火后，x射线衍射和磁力显微镜分析发现，在碳基质中生成了面心四方相的CoPt(FePt)纳米颗粒.对于特定组分为Co24Pt31C45和Fe43Pt35C22的薄膜，矫顽力以及颗粒尺寸都随退火温度的升高而增大，当退火温度为700℃时，Co24Pt31C45薄膜的矫顽力为21×105A/m，晶粒尺寸为17nm;当退火温度为650℃时，Fe43Pt35C22相应值分别为28×105A/m和105nm. 关键词： 磁记录材料 磁性薄膜 CoPt FePt纳米复合薄膜     

Preparation of LiMn2O4 thin films by a sol–gel method

LiMn₂O₄ thin films were prepared by a sol–gel method using spin-coating and annealing processes. Anhydrous Mn(CH₃COCHCOCH₃)₃ (manganese acetylacetonate) and LiCH₃COCHCO–CH₃ (lithium acetylacetonate) were chosen as source materials. The film electrochemical properties depended on the drying temperature even when subjected to the same annealing conditions. The discharge capacity of annealed film increased as the drying temperature was increased. However, the rate of capacity fading during cycling increased as the drying temperature was increased.     

Cu(In,Ga)Se2太阳能电池快速热退火效应

利用光致发光（PL）分析快速热退火对Cu(In,Ga)Se2 (CIGS)电池的影响,研究退火对薄膜缺陷的影响。Cu(In,Ga)Se2电池的PL谱中总共有 7个峰,即2个可见波段峰和5个红外波段峰。退火温度较低,可减少薄膜体内缺陷,提高载流子浓度,改善薄膜质量;退火温度过高,则会引起正常格点处元素扩散,元素化学计量比改变,体内缺陷增加,吸收层带隙降低,反而会对CIGS薄膜造成破坏。     

Solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface

The solid-phase synthesis of manganese silicides on the Si(100)2 × 1 surface coated at room temperature by a 2-nm-thick manganese film has been investigated using high-energy-resolution photoelectron spectroscopy with synchrotron radiation. The dynamics of variation of the phase composition and electronic structure of the near-surface region with increasing sample annealing temperature to 600°C, has been revealed. It has been shown that, under these conditions, a solid solution of silicon in manganese, metallic manganese monosilicide MnSi, and semiconductor silicide MnSi_1.7 are successively formed on the silicon surface. The films of both silicides are not continuous, with the fraction of the substrate surface occupied by them decreasing with increasing annealing temperature. The binding energies of the Si 2p and Mn 3p electrons in the compounds synthesized have been determined.