Observation of coupled magnetic and electric domains

Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.     

衬底负偏压溅射对ZrN薄膜性能的影响研究

本文采用S-抢磁控溅射系统淀积ZrN薄膜,用扫描电镜、X射线衍射、反射电子衍射、俄歇电子能谱和电学测量等方法研究了衬底负偏压溅射和溅射两种工艺方法淀积的ZrN薄膜的结构、组分和薄膜电阻率。结果表明,适当增大溅射功率,采用衬底负偏压溅射方法,有效地减少了氧的沾污,使得所淀积的ZrN薄膜的电学性能有明显改善。     

准一维有机铁磁体中的自旋耦合

应用Peierls-Hubbard模型研究了一种结构类似于poly-BIPO的准一维有机铁磁体。采用Hartree-Fock近似和周期性边界条件,探讨了最近邻相互作用和次近邻相互作用对系统的铁磁基态的影响。由于最近邻与次近邻相互作用之间的竞争,导致主链上相邻格点的自旋发生反铁磁耦合→铁磁耦合的变化,形成反铁磁自旋波或铁磁自旋波作为传递媒介,使自由基自旋得以平行排列,得到高自旋的铁磁基态。     

铁磁180°畴层结构中的畴层振动模

本文探讨了具有反平行磁化矢量的铁磁层状结构的磁畴振动谱,给出了普遍的色散方程.当外加磁场为零,整个分布成180°畴层状态时,给出了一般的色散曲钱.理论预言可能同时存在一种具有二维铁磁性和一维反铁磁性的新型磁有序材料.     

钙离子 A 位固溶改性钛酸铅多晶体的微观结构及响应特性

由于钙离子Ａ位固溶改性钛酸铅烧结多晶材料具有压电各向异性和其它优良的电学性能，所以该材料可广泛应用于制造高频超声换能器、红外检测器和声表面波（ＳＡＷ）器件。应用透射电镜（ＴＥＭ）技术、高分辨率成像技术和Ｘ－射线衍射技术，研究了材料的晶体结构和电畴形态对钙Ａ位固溶改性钛酸铅多晶体的晶体各向异性、压电各向异性和其它电学性质的影响。实验结果发现，高压电极化引起的晶体内部微裂纹，是引起横向机电耦合效应为零的钙离子Ａ位固溶改性钛酸铅多晶压电振子在厚度振动基频附近产生无规律小振幅振动（即假响应）的原因。     

Oscillatory dependence of current-driven magnetic domain wall motion on current pulse length

Magnetic domain walls, in which the magnetization direction varies continuously from one direction to another, have long been objects of considerable interest. New concepts for devices based on such domain walls are made possible by the direct manipulation of the walls using spin-polarized electrical current through the phenomenon of spin momentum transfer. Most experiments to date have considered the current-driven motion of domain walls under quasi-static conditions, whereas for technological applications, the walls must be moved on much shorter timescales. Here we show that the motion of domain walls under nanosecond-long current pulses is surprisingly sensitive to the pulse length. In particular, we find that the probability of dislodging a domain wall, confined to a pinning site in a permalloy nanowire, oscillates with the length of the current pulse, with a period of just a few nanoseconds. Using an analytical model and micromagnetic simulations, we show that this behaviour is connected to a current-induced oscillatory motion of the domain wall. The period is determined by the wall's mass and the slope of the confining potential. When the current is turned off during phases of the domain wall motion when it has enough momentum, the domain wall is driven out of the confining potential in the opposite direction to the flow of spin angular momentum. This dynamic amplification effect could be exploited in magnetic nanodevices based on domain wall motion.     

Stable ultrahigh-density magneto-optical recordings using introduced linear defects

The stability of data bits in magnetic recording media at ultra-high densities is compromised by the thermal 'flips'--magnetic spin reversals--of nano-sized spin domains, which erase the stored information. Media that are magnetized perpendicular to the plane of the film, such as ultrathin cobalt films or multilayered structures, are more stable against thermal self-erasure than conventional memory devices. In this context, magneto-optical memories seem particularly promising for ultrahigh-density recording on portable disks, and bit densities of approximately 100 Gbit inch(-2) (ref. 7) have been demonstrated using recent advances in the bit writing and reading techniques. But the roughness and mobility of the magnetic domain walls prevents closer packing of the magnetic bits, and therefore presents a challenge to reaching even higher bit densities. Here we report that the strain imposed by a linear defect in a magnetic thin film can smooth rough domain walls over regions hundreds of micrometres in size, and halt their motion. A scaling analysis of this process, based on the generic physics of disorder-controlled elastic lines, points to a simple way by which magnetic media might be prepared that can store data at densities in excess of 1 Tbit inch(-2).     

低变质原生结构煤电阻率变化规律实验研究

为了研究各个因素对煤电学性质的影响,利用电学方法通过电学参数来反映煤电阻率的变化规律。通过采用自主研制的煤体电阻率测试系统,用实验的方法对大佛寺井田低变质原生结构煤研究了应力作用时间、应力大小、甲烷气体吸附量以及含水率对煤体电阻率的影响。研究结果表明:煤体电阻率随应力作用时间先快速下降,后逐渐趋于稳定;应力越大,电阻率越小,吸附甲烷气体的量越多电阻率下降程度越大;含水率的提高也会造成煤体电阻率下降。最后基于灰色关联法分析了应力大小、应力作用时间、甲烷吸附量、含水率与煤体电阻率变化量的关联情况,从关联度可以看出应力大小是影响煤体电阻率变化的最主要因素。研究结果对于煤的导电特性研究具有一定的参考价值。     

单粒子各向异性S=1 Heisenberg反铁磁链的热力学性质

在自洽的自旋波理论框架下，探讨了单粒子各向异性Ｓ＝１Ｈｅｉｓｅｎｂｅｒｇ反铁磁链的热力学能，能隙及关联长度等热力学性质，并与数值模拟和实验进行了比较。     

Direct observation of the alignment of ferromagnetic spins by antiferromagnetic spins

The arrangement of spins at interfaces in a layered magnetic material often has an important effect on the properties of the material. One example of this is the directional coupling between the spins in an antiferromagnet and those in an adjacent ferromagnet, an effect first discovered in 1956 and referred to as exchange bias. Because of its technological importance for the development of advanced devices such as magnetic read heads and magnetic memory cells, this phenomenon has received much attention. Despite extensive studies, however, exchange bias is still poorly understood, largely due to the lack of techniques capable of providing detailed information about the arrangement of magnetic moments near interfaces. Here we present polarization-dependent X-ray magnetic dichroism spectro-microscopy that reveals the micromagnetic structure on both sides of a ferromagnetic-antiferromagnetic interface. Images of thin ferromagnetic Co films grown on antiferromagnetic LaFeO3 show a direct link between the arrangement of spins in each material. Remanent hysteresis loops, recorded for individual ferromagnetic domains, show a local exchange bias. Our results imply that the alignment of the ferromagnetic spins is determined, domain by domain, by the spin directions in the underlying antiferromagnetic layer.     

具有次近邻相互作用的面心立方格子的Ising(自旋S=1)反铁磁薄膜在外场下的基态自旋结构

将文献[5]的方法推广到反铁磁薄膜,变S=1的Ising体系成一个粒子数不守恒的费米体系,严格得到fcc格子的反铁磁薄膜在外场下的基态,并给出了其交换积分在一定范围内的零温相图。从中可见其自旋状态与大块铁磁体的差别,表面自旋排列存在与内部不同的方式。这是由于系统不再具有垂直于表面方向的平移对称性而产生的非均匀效应。     

薄膜畴壁自旋波耦合栅格设计

用保角变换分析计算了坡莫合金栅格在均匀磁场作用下产生的二级磁场．以此为依据设计了用于薄膜畴壁内自旋波Ｗｉｎｔｅｒ模式激发的能量耦合栅格．制得的栅格在Ｗｉｎｔｅｒ模式研究中获得满意的效果,实现了激励电磁场与自旋波的成功耦合,首次测得自旋波Ｗｉｎｔｅｒ模式谱．     

La0.7Sr0.3MnO3外延膜厚度引起的电阻率变化

不同厚度的La0.7Sr0.3MnO3(LSMO)外延薄膜被沉积到立方相的LaA lO3(001)单晶衬底上,XRD测试结果显示,LSMO外延膜的结构是单相的,具有与衬底相同的晶格取向;随着膜厚的增加,LSMO外延膜的晶格经历应变到驰豫的变化.电阻测量显示,应变驰豫的薄膜(较厚的薄膜)有较大的电阻率,这与该膜中缺陷浓度增加有关.此外,也对生长在不同单晶衬底上的LSMO外延膜(厚度相同)的结构和电阻进行了对比研究.     

储层厚度和电阻率对海洋可控源电磁法的影响分析

随着海底油气资源勘探的进行,海洋可控源电磁法（CSEM）成为研究的热点。本文采用二维自适应有限元正演程序MARE2DCSEM,建立正演模型,模拟了不同厚度、电阻率对异常的影响。模拟结果表明：厚度一定时,MVO曲线和电阻率先成正比例,而在达到最大响应的收发距时则随之减少;电阻率相同时,厚度从小渐渐增大时,MVO曲线逐渐增大,在达到最大响应的收发距时则随之减小;储层厚度和电阻率变化是一个体积效应,当乘积相同时,归一化曲线差别很小,大约在2%左右,这为反演提供了理论依据。     

自旋梯状化合物Sr14(Cu1-xZnx)24O41的电输运及磁学性质

采用标准固相反应法制备了Sr14(Cu1-xZnx)24O41(x=0, 0. 01, 0. 02, 0. 03)系列多晶样品. X射线衍射谱表明所有样品均呈单相,且样品晶格常数大小随Zn掺杂量x的变化存在微弱波动. X射线光电子能谱表明Sr14Cu24O41中Cu离子以+2价形式存在,Zn掺杂对体系中Cu离子化合价不造成影响. 磁化率测量结果表明在10~300 K温度范围内Zn掺杂使体系磁化率降低,拟合结果表明随着Zn掺杂量x的增大,居里-外斯项对体系磁化率贡献逐渐减弱,二聚体耦合能JD 逐渐降低,每个分子中CuO2 自旋链内二聚体个数ND 与自由Cu2+离子自旋数NF 均逐渐减少,进一步分析显示替换二聚体内Cu2+离子的Zn2+离子数少于替换自由Cu2+离子的Zn2+离子数. 电阻率测量结果表明Sr14Cu24O41体系具有半导体特性,并且Zn掺杂会使体系电阻率降低,降低程度随掺杂量x增大而增大,但并未使体系发生金属- 绝缘体转变. 认为电阻率降低可能是由于Zn2+离子掺杂使体系内CuO2 自旋链中二聚体发生退耦,破坏了电荷有序超结构,从而使更多的空穴释放出来并转移到导电性好的Cu2O3自旋梯子中所致.     

成分对CoCr薄膜磁畴影响的研究

对Cr含量为0-23 at％的不同成分系列的CoCr合金薄膜磁畴的研究表明,随着Cr成分增多时其磁各向异性和相关的磁畴结构都敏感地变化。当Cr含量少于17at％时,面内磁化强度为主,并有多种结构形式。超过Cr含量11.2 at％后,少量的垂直磁化强度点畴出现,并随Cr含量增多而增多。Cr含量在17-23 at％的范围内可获得垂直磁各向异性为主的CoCr膜,也可能得到用于高密度垂直磁记录的优良薄膜磁性能。显微照片显示了点畴的尺寸比膜表面的晶粒的或膜断面的晶柱的尺寸都大些。因此,可以得出结论,即其一个自发磁化强度点畴是由一束晶柱或长成的晶粒组成,并都处在单畴状态。     

铬酸钒为基的PTC陶瓷的研究

本文使用ＳＥＭ、ＥＤＳ、ＥＡＳ、ＸＲＤ和电阻率测量技术，研究了工艺参数和加入（Ｃｏ，Ｆｅ２Ｏ３）对ＰＴＣ（Ｖ１－ｘ，Ｃｒｘ）２Ｏ３陶瓷的显微结构和电性能的影响。实验结果表明，为了制造优良性能、高可靠的热敏电阻器，必须精确控制陶瓷组份和工艺。引人象Ｃ。这样的添加物是重要的，它主要以金属形式分布在基体中，同时发现添加物对试样致密度和电性能的影响也是有益的。     

铝铜合金阳极氧化新工艺

在低浓度复合电解液中,利用分阶段升压技术,高温下在阳极氧化较难的铝铜合金LY12上制备了具有较高厚度、硬度和良好外观的银白色氧化膜层．实验研究了各工艺参数对膜层性能的影响．结果表明：磷酸是主要成膜物质;由定量的有机羟酸和导电盐组成的添加剂可大大提高膜层的厚度;电流密度的大小对膜层性能影响较大;采用分阶段升压方式可使电流密度在较长时间内保持较大的值;阳极氧化电压,氧化温度及氧化时间等对成膜过程也有一定影响．     

砂浆特性参数对硅酸根电迁移反应法致密化和表面涂覆效果影响

采用硅酸根电迁移反应法致密化和表面涂覆砂浆,研究了水胶比、矿物掺和料、养护龄期和试件厚度等砂浆特性参数对被处理砂浆试件表面涂层厚度、抗压强度与抗折强度、电阻率的影响。结果表明:随着水胶比的减小与养护龄期的延长,砂浆试件生成的表面涂层增厚,抗压强度与抗折强度、电阻率提升增大;加入掺合料的砂浆试件形成的涂层厚度和电阻率大小顺序为硅粉矿粉无掺合料粉煤灰,掺硅粉与矿粉的砂浆试件电阻率出现的峰值时间早于无掺合料试件;硅粉砂浆试件的抗压强度、抗折强度增幅大于无掺合料砂浆,而粉煤灰砂浆试件抗压强度与抗折强度变化不明显;砂浆试件厚度对于硅酸根电迁移反应法处理的砂浆性能影响不明显。