R3(Fe,Mo)29Nx的晶体学特性和内禀磁性

研究了R₃(Fe,Mo)₂₉(R=Ce,Nd,Sm,Gd,Tb,Dy,Y)氮化物的晶体学特性和内禀磁性.主要研究内容为：氮化对R₃(Fe,Mo)₂₉金属间化合物的点阵参数、居里温度T_C、饱和磁化强度σ_s和各向异性场B_a的影响. 关键词：     

高磁电阻磁性隧道结的几种微制备方法研究

利用金属掩模法优化了制备磁性隧道结的实验和工艺条件，金属掩模的狭缝宽度为100 μm. 采用4 nm厚的Co₇₅Fe₂₅为铁磁电极和10或08 nm厚的铝氧化物 为势垒膜， 直接制备出了室温隧穿磁电阻（TMR）为30%—48％的磁性隧道结，其结构为Ta(5 nm)/Cu(25 nm)/Ni₇₉Fe₂₁(5 nm)/Ir₂₂Mn₇₈(10 nm)/ Co₇₅Fe₂₅ (4 nm)/Al(08 nm)-O/Co₇₅Fe₂₅(4 nm)/Ni₇₉Fe ₂₁(20 nm)/Ta(5 nm).同时，利用刻槽打孔法和去胶掀离法两种光刻技术并结合Ar离子束刻蚀及化学反应刻 蚀，制备出面积在4 μm×8 μm—20 μm×40 μm、具有室温高TMR和低电阻的高质量磁性 隧道结.300 ℃ 退火前后其室温TMR可分别达到22% 和50%.研究结果表明，采用光刻中的刻 槽打孔或去胶掀离工艺方法制备的小尺寸磁性隧道结，可用于研制磁动态随机存储器和磁读 出头及其他传感器件的磁敏单元. 关键词： 磁性隧道结 隧穿磁电阻 金属掩模法 光刻法     

成分调制的La1-xSrx MnO3复合隧道结

利用磁控溅射和Sr成分的调制以及原位热处理方法,在10mm×10mm大小的(001)取向SrTiO3单晶衬底上制备出三明治结构为La0.7Sr0.3MnO3(100nm)/La0.96Sr0.04MnO3(5nm)/La0.7Sr0.3MnO3(100nm)的隧道结外延薄膜,然后再次利用磁控溅射方法,在三层单晶膜上方继续沉积Ir22Mn78(15nm)/Ni79Fe21(5nm)/Pt(20nm)等金属三层膜.最后利用深紫外曝光和Ar离子束刻蚀等微加工技术,制备出长短轴分别为12和6μm或者8和4μm大小的椭圆形La1-xSrxMnO3成分调制的复合磁性隧道结.在4.2K和外加磁场8 T的测试下,La1-xSrxMnO3成分调制的复合磁性隧道结其隧穿磁电阻(TMR)比值达到3270%,直接从实验上证实了铁磁性La07Sr0.3MnO3金属氧化物的自旋极化率(97%)可接近100%,具有很好的半金属性质.     

CoFeB/AlOx/Ta及AlOx/CoFeB/Ta结构中垂直易磁化效应的研究

本文详细研究了在不同氧化层和铁磁层厚度情况下, 底层CoFeB/AlO_x/Ta结构和 顶层AlO_x/CoFeB/Ta结构中的垂直磁各向异性. 在底层CoFeB/AlO_x/Ta结构中观察到了垂直磁化的磁滞回线, 证明了其垂直易磁化效应的存在; 而在顶层AlO_x/CoFeB/Ta结构中却没有观察到类似的磁滞回线. 对这种对称结构中的非对称现象进行了分析. 研究还发现不同的氧化层和铁磁层厚度均会影响层间界面相互作用的强度, 从而导致结构的垂直磁化曲线矫顽力大小发生改变. 这项研究将对基于AlO_x氧化层垂直磁隧道结的研制具有重要的意义. 关键词： 垂直磁各向异性 磁隧道结 随机存储器     

Abnormal magnetoresistance behavior in Nb thin film with rectangular arrays of antidots

Magnetoresistance in superconducting Nb films perforated with rectangular arrays of antidots (holes) is investigated at various temperatures and currents. Normally, the magnetoresistance increases with the increasing magnetic field. In this paper, we report a reverse behavior in a certain range of high fields after vortex reconfiguration transition, where the resistances at non-matching fields are smaller than those in the low field regime. This phenomenon is due to a strong caging effect, in which the interstitial vortices are trapped among the pinned multiquanta vortices. This effect is temperature and current dependent.     

Role of defects in magnetic properties of Fe-doped SnO2 films fabricated by the Sol--Gel method

This paper obtains the room temperature ferromagnetism in Sn1 xFexO2 films fabricated by the Sol-Gel method.X-ray diffraction results show that Fe doping inhibits the growth of SnO2 and Fe3+ ions occupy the Sn sites.The measurement of resistance excludes the free carrier inducing ferromagnetism.Moreover,the temperature dependence of magnetization has been better fitted by the Curie-Weiss law and bound magnetic polaron(BMP) theory.An enhancement of ferromagnetism is achieved by annealing the samples with x = 7.1% in H2,and a decrease of oxygen flow rate.All these results prove that the BMP model depending on defects can explain ferromagnetism in diluted magnetic oxides.     

MgO单晶势垒磁性隧道结的第一性原理计算和实验研究

在MgO单晶势垒磁性隧道结中发现的室温高隧穿磁电阻现象,是近些年自旋电子学以及磁性隧道结磁电阻材料研究中的又一重大突破.本文主要评述和介绍2001年以来MgO单晶势垒磁性隧道结第一性原理计算和实验上的重要进展,以及介绍利用Layer-KKR第一性原理计算方法研究的Fe(001)/MgO/Fe、Fe(001)/FeO/MgO/Fe、Fe(001)/Mg/MgO/Fe、Fe(001)/Co/MgO/Co/Fe和Fe(001)[MgO/Fe/MgO/Fe等基于单晶MgO(001)单势垒及双势垒磁性隧道结材料的电子结构和自旋相关输运性质研究的最新进展.这些第一性原理定量计算的结果,不仅从物理上增强了对MgO单晶势垒磁性隧道结的电子结构和自旋相关输运特性的了解,而且对于研究新型室温磁电阻隧道结材料及其在自旋电子学器件中的广泛应用,具有一定的参考价值.     

基于磁性绝缘体的磁子阀效应

正晶体管是现代半导体器件的基石,计算机芯片通过晶体管来控制其中的电子流动。为了进一步提高计算机的存储密度与运算速度,人们迫切需要发展更小尺寸的晶体管单元。如今微电子技术已经跨入10 nm的制程工艺,由于面临原子极限和量子效应等物理瓶颈,继续向下推进新的制程节点变得越来越困难。为了继续提高半导体器件的性能,研究人员正在努力寻求新的替代方案。面向后摩尔时代的信息存储与逻辑运算需求,自旋电子器件(Spintronic Device)为开发下一     

Correlation between Electroresistance and Magnetoresistance in Slight Oxygen-Deficient Nd0.67Sr0.33MnO3-δ Polycrystalline Ceramics

A colossal electroresistance effect is found in Nd0.67Sr0.33MnO3-δ polycrystalline ceramics with a very slight oxygen deficiency ~ ~ 0.05. The electroresistance behaviour of Nd0.67Sr0.33MnO3-δ（δ= 0.05） displays the striking similarity to its counterpart magnetoresisnce. It reveals that the boundary effect plays an important role in electroresistance and the same physical origin is likely responsible for both magnetoresistance and electroresistance effects in Nd0.67Sr0.33MnO3-δ polycrystals.     

ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y,La, Ce,Pr, Nd,Sm, Gd,and Tb)

Self consistent charge and spin polarized local spin-density approximation functional theory calculations based on the discrete variational method have been performed for RCo₅(R=Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) compounds. The partial density of states of the Pr atom in the PrCo₆Co₁₂ cluster is established to be strikingly similar to that of the Ce atom in the CeCo₆Co₁₂ cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii ＜r_4f＞ and ＜r₄f²＞ of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthanide contraction. The crystalline electric field (CEF) parameter A⁰₂ at the R site is calculated using a real charge distribution ρ(R) in the cluster, except for Pr and Nd, and is in agreement with that evalu ated based on the single-ion model. This result shows that the CEF parameter A⁰₂ is mainly determined by the near electronic structure. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitals in some single-electron-molecular-orbitals, which are n ear the Fermi energy level and occupied by electrons. For light rare-earths the R-4f electrons in R Co₆Co₁₂(R=Y, La, Ce, Pr, Nd, and Sm) clu sters are not localized entirely and a small amount of the R-4f electrons have itinerant properties.