Ni52Mn24Ga24单晶中取向内应力的热动力学计算

作者来商丘师范学院物理系崔玉亭副教授和中国科学院物理研究所磁学国家重.点实验室柳祝红,王文洪等,全文发表于SCI源期刊(物理学报》2003年第52卷第7期(P1726一1730),该文系国家自然科学基金(批准号:50131010)资助课题. 测量了Ni52Mn24Ga24单晶样品在磁场加载和未加载下马氏体相变时的相变应变.分析结果表明:用提拉法生长单晶时在晶体内部引入了单一取向的内应力,该取向内应力可诱导马氏体变体择优取向,从而导致马氏体相变时产生大的相变应变.从理论上计算了该取向内应力的大小.另外,对样品在马氏体态单纯磁诱导应变的热动力学研究,表明…     

铁磁形状记忆合金孪晶界移动摩擦耗能的热动力学计算

测量了在不同温度下Ni52Mn24.5Ga23.5单晶的磁感生应变。在280 K（略低于马氏体相变完成温度）测量得到的磁感生应变量高达-1.2%;随着温度的降低,磁感生应变量迅速减小;在250 K温度下,磁感生应变量仅为-0.37%,说明NiMnGa材料的磁感生应变具有明显的温度依赖性。此外,根据热力学理论,计算了不同温度下,磁感生应变过程中孪晶界移动的能量损耗。结果表明,磁感生应变量可定性反映一个循环过程中孪晶界移动的能量损耗的大小。     

磁场对NiMnGa单晶预相变温度的影响

利用应变测量研究了外加恒定磁场对NiMnGa单晶预相变温度的影响,发现外加磁场使预相变温度向低温方向漂移,而且预相变温度漂移的程度与外加磁场的方向有关.依据前人的模型和我们的电子显微镜观察,目前的结果证实预相变过程中存在较强的磁弹相互作用;当外加磁场分别沿晶体的[001]和[010]两个等价的晶轴方向时,在[010]方向上导致的磁弹相互作用更强.     

NiCoMnSb合金的相变和多功能特性研究

采用电弧熔炼和高温退火的方法制备了Ni_(42)Co_8Mn_(39)Sb_(11)铁磁形状记忆合金.用X射线衍射表征样品的晶体结构,用综合物性测试系统对材料的马氏体相变以及马氏体相变附近的磁热效应、磁电阻效应和磁致应变效应进行了表征.结果表明,样品在220 K左右发生了从弱磁马氏体到铁磁奥氏体的相变,随磁场增加,马氏体转变温度向低温偏移.在马氏体相变附近,样品不仅具有较大的磁热效应,还具有磁电阻效应和磁致应变效应,这些效应都是由磁场驱动马氏体相变导致的.这些结果说明Ni-Co-Mn-Sb合金在磁制冷、磁传感、磁驱动领域有着潜在的应用.     

Ta_2Co_4O_9的低温磁介电及磁电性质研究

利用高温固相反应法制备Ta_2Co_4O_9多晶样品,并对其磁性、介电及磁电耦合性能进行了研究.结果表明,磁场作用下的介电温谱在磁相变温度(20 K)附近出现异常,且异常峰的强度随着外加磁场的增加而增强.与此同时,还观测到关于磁场线性增强的电极化,表明该材料具有线性磁电耦合效应.     

二维层状磁性半导体材料FePS_3的物理性质研究

利用化学气相输运法制备出了过渡金属-磷-三硫化物FePS_3的高质量单晶样品,并对该单晶样品的晶体结构、电输运性质和磁各向异性进行了系统的研究.粉末X射线衍射结构精修显示FePS_3呈单斜晶体结构,具有典型的层状结构特征.面内电阻率随温度降低而升高,呈半导体行为,激活能大小为273 meV.在高温区,面内磁化率和面间磁化率都随温度降低而升高,呈居里-外斯顺磁行为;但是两个方向上磁化率的外斯温度符号相反,表现出明显的各向异性.随着温度的降低,两个方向上的磁化率在118 K附近都急剧减小,然后保持不变,表现出典型的反铁磁相变行为,但是该反铁磁相变具有明显的一级相变特征.     

隧道磁电阻效应磁场测量方法研究

提出了一种采用三轴隧道磁电阻传感器作为测量探头,双轴定向、单轴独立测量的三维磁场测量方法。测量时转动测量探头,使两定向轴输出电压均为零,此时独立测量轴与磁场方向一致,实现独立轴直接测量总磁场。利用曲线拟合,获得了测量探头的输出电压与磁感应强度在一定范围内的线性函数关系。通电螺线管中心轴线上磁感应强度测量实验结果表明,采用该方法的测量系统,测量±0.3T范围内的磁场,最大相对误差为-4.3%,精确度高于0.3%。     

LaCaSrMnO_3薄膜性能的实验研究

利用PLD方法,在倾斜LaAIO,单晶衬底上镀制了'LaCaSrMnO3薄膜.对该薄膜进行了LITV信号测量,表明其LITV信号上升沿和脉冲宽度都比LCMO薄膜小,可以用来制作更快响应的光探测器件;对该薄膜进行了R-T关系测量,其金属-绝缘体转变点为313K.     

反铁磁半金属GdSb中极大磁电阻效应研究

具有极大磁电阻的半金属材料因其可能具有非寻常的拓扑电子结构、电输运特性,可为高能物理相关的狄拉克费米子、外尔费米子以及马约拉纳费米子的研究提供崭新的舞台,受到了广泛关注.本文通过助溶剂法合成高质量的GdSb单晶并系统地研究其结构、磁性、电输运等性质,发现该材料具有NaCl型晶体结构(空间群Fm-3m),并且在23.4 K附近经历反铁磁相变.电输运结果表明GdSb具有金属导电性,自旋无序效应可导致磁相变温度附近的电阻出现异常.更吸引人的是,样品在磁场(H=9 T)作用下,低温(2 K)电阻将出现平台,展示出极大的磁电阻效应(MR=12 100%).通过霍尔效应及第一性原理计算,发现GdSb是多带及补偿型半金属,其中电子与空穴的数目相当.电子-空穴补偿及较大的载流子迁移率是极大磁电阻的来源.     

无取向硅钢热轧组织演变规律的研究

运用形变储能、层错能、交滑移、相变、形变诱导相变和析出、相变应力应变诱导再结晶等概念和有关原理探讨了热轧组织演变规律,并分析了4种不同成分钢种热轧组织的形成机理.     

Phase transition characteristics of the Ni46Mn35Ga19 single crystal

The phase transition characteristics of the prepared Ni46Mn35Ga19 single crystal have been systematically investigated by measuring resistance, strain, heat flow, and ac magnetic susceptibility. The experimental results indicate that both magnetic transition and martensitic transformation occurred simultaneously and the corresponding transition temperature was about 356 K. Meanwhile, the prepared single crystal also exhibited spontaneous and magnetic-field-enhanced two-way thermal shape memory effect with the strains up to -0.89% and -1.90% with and without a magnetic field of 1.6 T, respectively. The possible mechanism of the large spontaneous and magnetic enhanced deformation were analyzed based on the phase transition characteristics of Ni46Mn35Ga19 single crystal and the preferential orientation of martensitic variants.     

Ni-Mn-Co-Sn铁磁形状记忆合金的磁性、相变及磁热效应

采用电弧熔炼的方法制备了Ni43Mn46-xCoxSn1,系列铁磁形状记忆合金,并对其磁性和相变进行了研究．结果表明,由于价电子浓度的增加,Co替代Mn使材料马氏体转变温度迅速提高．Co的加入使合金的奥氏体居里温度迅速提高,而马氏体居里温度则略有降低．在马氏体相变附近,由于磁化强度的突变,合金表现出巨大的逆磁热效应,表明该系列合金在磁制冷领域有着潜在的应用价值．     

Fe-16Mn-3.5C-3Si-3Cu高锰TWIP合金铸铁的热处理金相组织分析

通过改变加热温度和保温时间,研究不同热处理工艺对Fe－16Mn－3.5C－3Si－3Cu高锰TWIP合金铸铁组织的影响,对试样进行物相分析和金相组织观察。实验结果表明:随着加热温度和保温时间的增加,组织中退火孪晶的数量增加,孪晶发育趋于完善。热处理后其室温组织为单一奥氏体;热处理的合金铸铁拉伸变形后,产生大量形变孪晶,其变形后的基体仍然保持单一奥氏体组织,未发生马氏体相变,发生了完全的TWIP效应。     

自制磁通门传感器测量弱磁场

基于磁通门传感器的基本原理,提出了一种新颖的三维磁场的测量方法,通过探头的三维转动来测量弱磁场矢量在三个正交方向的大小,以此来得出合场强矢量。该种方法是基于软磁材料磁化非线性特性原理,通过多个电路模块进行数据收集以及处理来测量小于1 mT弱磁场。     

高锰含量Mn50＋xNi41-xSn9合金的相变和磁热效应

采用电弧熔炼方法制备了Mn50＋xNi41-xSn9系列铁磁形状记忆合金,并对其磁性、相变和磁热效应进行了研究。结果表明,合金在室温下均表现为四方马氏体相和立方奥氏体相的混合相,随着Mn含量的增加,由于价电子浓度的减少,马氏体转变温度逐渐下降,当x=2—4时,马氏体相变伴随着较大磁化强度的突变,同时合金表现出较大的逆磁热效应,这表明该系列合金在磁制冷领域有着潜在的应用价值。     

Fe含量对Ni-Fe-Ga合金马氏体相变的影响

利用金相显微技术和示差扫描量热法研究了合金成分对Ni-Fe-Ga铁磁形状记忆合金马氏体相变的影响,用X射线衍射方法分析了马氏体的结构类型.研究发现,Ni代替Fe显著提高合金的马氏体相变温度,每1%Ni可以使合金马氏体相变温度提高约40 K.X射线衍射表明Ni73.5-yFeyGa26.5合金773K真空退火后都只出现4M型晶体结构的马氏体.     

Magnetic compass orientation in C57BL/6J mice

We report evidence for a robust magnetic compass response in C57BL/6J mice. Mice were trained to build their nests in one of four magnetic directions by creating a light gradient along the long axis of a rectangular cage and positioning a nest box at the opposite (dark) end. The mice were then tested overnight in a circular, visually symmetrical arena in one of four magnetic field alignments. The positions of the nests built in the test arena showed strong unimodal orientation in the magnetic direction coinciding with the dark end of the training cage.     

Mechanisms for turn alternation in woodlice (Porcellio scaber): The role of bilaterally asymmetrical leg movements

Angles of free turn were observed in woodlice (Porcellio scaber) after they had been forced to turn left or right in runways. Alternation angles were increased by greater forced-turn angles and number of successive forced turns in one direction. Removal of one or both antennae had no effect on alternation. It was also repeatedly observed that the closer a woodlouse remained to the far wall while traveling along the exit alley of a runway, the greater was its angle of alternation. However, orientation toward this far wall bore no relation to alternation. When given three successive left or right forced turns followed by a fourth in the opposite direction, woodlice moved further away from the exit-alley far wall and repeated the last forced turn at the choice area. Along with results of the other experiments, this result in particular supported an explanation for woodlouse alternation based on bilaterally asymmetrical leg movements (BALM) arising from the negotiation of forced turns. Such asymmetry is seen as biasing an animal to turn in the opposite direction to a preceding forced turn.     

The influence of children's prior knowledge and previous experience on their spatial orientation skills in an urban environment

This study investigates the capacity of children to develop map-based skills in spatial orientation in an urban environment unknown to them. In this quantitative study, a total of 328 pupils of grades 3–5 had to achieve specific skills with regard to map-based skills in spatial orientation (such as turning-off skills, transformation from map to place, finding one's direction, navigation). These skills were tested by means of a map of Münster (Westphalia, Germany). This paper focuses on factors of potential influence, such as prior knowledge in the field of map reading as well as family- and school-related previous experience.