Multiferroic phase transitions in manganites RMnO3: A two-orbital double exchange simulation

The semi-quantum two-orbital exchange model is used to investigate the effect of small rare-earth ion substitution on orthorhombic RMnO 3 with A-type antiferromagnetic order,using the Monte Carlo algorithm,exact diagonalization,and zero-temperature optimization approaches.It is revealed that the substitution results in a rich multiferroic phase diagram where the coexisting A-type antiferromagnetic phase and spiral spin phase,pure spiral spin phase,coexisting spiral spin phase,the E-type antiferromagnetic phase,and the pure E-type antiferromagnetic phase emerge in sequence.The multiferroic phase transitions modulate substantially the electric polarization,which is consistent qualitatively with recent experiments.     

铁电磁体Pb(Fe1/2Nb1/2)O3相变特征

借助与示差扫描量热法、磁化率测量、电子自旋共振、铁电与介电性质测量及电子衍射系统地研究了Pb(Fe_1/2Nb_1/2)O₃(PFN)的电、磁性质和相变特征．结果表明发生在380K附近的顺电－铁电转变和发生在145K附近的顺磁 反铁磁转变分别为一级相变和二级相变或弱一级相变．在室温下,PFN的剩余极化与矫顽场分别为11.5μC/cm²和3.04kV/cm.介电测量表明PFN的顺电-铁电相变为弥散型相变．其弥散指数为1.62.电子衍射表明Fe³⁺与Nb⁵⁺离子在B位置上是无序分布的,正是这种与无序分布相关联的成分涨落导致铁电相变的弥散性. 关键词：     

以“电磁学”为例谈专业课程思政成为滋润学生成长沃土

本文以“电磁学”课程为例,讨论了做好课程建设,把唯物主义、从实践中来到实践中去、实事求是等思政元素融入专业课程教学的方法,把“三个面向”植入学生心田,使之在不知不觉中生根发芽,推进课程育人.     

Ferroelectricity in a diatomic Ising chain as investigated by the elastic Ising model

An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca₃CoMnO₆, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca₃Co_2-xMn_xO₆ (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment.     

SCALING LAW FOR CBr4-C2Cl6 LAMELLAR EUTECTIC IN DIRECTIONAL SOLIDIFICATION

A coupling equation of directional solidification of CBr₄(α)-C₂Cl₆(β) eutectic is solved numerically. Profiles and profile bifurcation of the solidifying interface as functions of the interlamellar spacing are studied in detail. It is believed that the critical bifurcating point of the solidifying interface of each lamella coincides with its marginally stable position and hence, a new scaling law is derived. Existence of the band of spacing selection is also studied. For a given solidifying rate, the critical bifurcating point of β/liquid interface is the upper limit of this band, and its lower limit corresponds to the critical bifurcating point of α/liquid interface. Our analyses interpret the latest relevant experimental data reasonably.     

多铁性纳米点结构及微纳器件应用

在当前电子技术微型化和高度集成化的趋势下,多铁性纳米材料的研究正逐渐成为一个重要主题。这方面的研究还处在起步阶段,在材料的制备工艺和表征手段方面还面临诸多挑战。文章简要介绍了多铁性纳米点的制备工艺(包括离子刻蚀、自组构、多孔氧化铝模板方法等)和以多功能扫描探针为代表的表征手段,还介绍了纳米点带来的新颖的物理现象及其在微纳器件应用等方面的研究进展。     

终终是关联关不住,贤纲秋水做文章

正我以为,物理学中最难的领域是凝聚态物理。基本粒子物理、核物理和高能物理,也许在学术上很难,但她们距离口味不同的百姓相当远,还能够"唯心主义"地发挥猜想的空间较大,受外部非科学的压力较小。凝聚态物理因为几个特征,一直以来"满是光芒尽是伤":(1)体系对象广泛,学者们素有喜新厌旧、见异思迁的秉性,所以凝聚态的新东西多、新故事好。     

放飞极性约束极性

致界面故人常问世间尘,维度为凭对称真。物理天生多界面,同年定论又重询。1.引子笔者无知,所以狂妄,此处斗胆认为从事研究工作的物理人大致可分两类:一类人,上杆子追求人类正在和未来需要什么、或被需要什么,以推动文明生活的进步为己任。一类人,打着兴趣的旗号,上杆子追求自己内心的呼唤与梦想,也以推动文明生活的进步为己任。这两种人的划分并非绝对,很多人可以享有双重身份,根据需要而随意互换。     

稀土掺杂锰氧化物庞磁电阻效应

过去十多年来,具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高,且在居里温度附近表现出很大的磁电阻效应,因此在自旋电子学中有潜在的应用前景。另一方面,锰氧化物是典型的强关联电子体系,它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构,简单介绍了其他一些庞磁电阻材料;随后综述了锰氧化物的电荷/轨道有序相及其输运性质;在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制;最后讨论了锰氧化物的一些可能的应用,如低场磁电阻效应、磁隧道结、磁p＿n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。     

多铁性材料:过去、现在、未来

2010年美国物理学会的James C.MeGroddy奖授予了三位美国科学家:加州大学圣芭芭拉分校Nicola A.Spaldin教授、罗格斯大学Sang-Wook Cheong教授和加州大学伯克利分校Ramamoorthy Ramesh教授,以表彰他们"在推进对多铁性氧化物的认识以及应用方面所作的奠基性贡献".2010年10月份的Physics Today(2010年第10期,第38-43页)刊登了这三位教授为此撰写的精彩文章,对多铁性材料研究的过去、现在和未来进行了评述与展望.全文主要内容如下: