SmFeAsO0.78F0.22中Mn掺杂对超导电性的抑制效应

本文报道了Mn替代Fe对最佳掺杂的Sm-1111体系超导电性的影响.通过电输运及磁性质的测量发现Mn对Fe的替代迅速抑制了超导电性.随着Mn含量的增加,体系的电阻率ρ和磁化率M逐渐增大.对于低掺杂x＜0.25%和未掺杂样品,M接近零,对于≤1%,M从室温到超导转变几乎不变,实验指出Fe2+失去其磁性.我们提出这是由于F...     

La1.85-xSr0.15+xCu1-xMxO4(M = Cr, Mn, Fe, Co, Ga, Al)体系的输运性质研究

利用Ｘ－光衍射,电阻率和电势等实验手段,系统地研究了Ｌａ１．８５－ｘＳｒ０．１５＋ｘＣｕ１－ｘＭｘＯ４（Ｍ＝Ｃｒ,Ｍｎ,Ｆｅ,Ｃｏ,Ｇａ ａｎｄ Ａｌ）体系的结构和输运性质。结果表明;所有的三阶离子掺杂都能在较低的掺杂浓度下抑制超导电性,并且引起金属到绝缘体的转变。磁性离子和非磁性离子掺杂引起显著不同的热电势变化,并用ｄ－ｐ杂化态的变化和局域自旋散射来进行分析讨论。     

Pb、La掺杂Bi2201相高质量单晶的生长和表征

自助熔法从富Ｂｉ２Ｏ３ 的Ｂｉ１ ．８ ＋ ｘＰｂ０ ．２Ｓｒ１ ．６５Ｌａ０ ．３５ＣｕＯｙ（ｘ＝ ０ ．１ ,０ ．２,０ ．３ ,０．４ ,０ ．５） 熔体中生长出了高质量的Ｐｂ、Ｌａ 掺杂的Ｂｉ２２０１ 相大单晶,最大尺寸达８ ×４ ×０ ．０５ｍｍ３ ．在生长单晶时不同程度过量的Ｂｉ２Ｏ３ 用作助熔剂,最佳助熔剂含量以及最佳温度控制过程被确定．通过单晶的（００ｌ） ＸＲａｙ 衍射和摇摆曲线以及电子衍射对一块尺寸为４ ×１ ．６ ×０ ．０３ｍｍ３ 的高质量单晶做了结构表征．由试验发现从富Ｂｉ２Ｏ３ 的熔体中生长高质量Ｂｉ２２０１ 相大单晶的关键是合适的助熔剂含量和温度控制过程     

层状过渡金属硫代亚磷酸盐材料的磁性研究

采用化学气相输运的方法生长了一系列的MPS_3(M=Mn,Fe,Ni)单晶样品.X射线衍射和电子能谱测试结果表明生长出来的样品是纯相并且单晶质量较好.MPS_3单晶样品在低温下均为反铁磁性.当磁场平行于面内时,磁化率—温度曲线在奈尔点以上存在一个较宽的峰值,可能与准二维磁交换导致的短程序有关.这些现象表明MPS_3体系是一个很好的研究二维材料磁性的平台.此前理论与实验结果显示该体系具有宽带隙,电阻率也很大.因此,MPS_3体系在二维层状材料介电方面有很大的应用前景.     

Non-Stoichiometry Effects on the Extreme Magnetoresistance in Weyl Semimetal WTe_2

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe_2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistance is strongly dependent on the residual resistivity ratio(i.e., the degree of non-stoichiometry),which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe_2.     

Transport properties in La0.7-xGdxSr0.3MnO3 system

The influence of Gd doping at La-site on the electrical transport properties and the colossal magnetoresistance of La0.7-xGdxSr0.3MnO3 (x = 0.00, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70) is studied. The experimental results indicate that the transport properties exhibit abnormal behavior under high doping condition. For x = 0.50, we find that a transition from metal to insulator occurs after the occurrence of insulator-metal transition near Tc, which seldom occurs in ABO3 structure. For samples x = 0.60 and 0.70, it exhibits insulator behavior far above Tc. These abnormal behaviors are attributed to different magnetic background, i.e. the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order.