La2-xSrxCuO4单晶膜的热电势与电阻率

测量了高质量的单晶膜La2-xSrxCuO4(x=010,020,025)的电阻率和热电势.La19Sr01CuO4电阻率呈现S型行为,表明存在一个赝能隙,在赝能隙态可以用公式ρ=ρ0+βexp(-ΔT)很好地拟合.热电势的测量表明,在超导转变前样品的残余热电势值非常小,这是膜的高质量引起的,三个样品在200K以上都出现一个宽峰,对其进行了一些理论模型分析,并与电子型超导体热电势结果作了比较.关键词：薄膜输运性质热电势     

La2CuO4在平行CuO2面磁场中的磁转变

本文在平均场近似下,给出一个关于在平行CuO₂面的磁场作用下,La₂CuO₄的磁转变理论。理论给出的临界磁场随温度T的变化,在定性上与实验相符。但是,从本文理论看,不存在多重临界点。简单讨论了理论和实验不符合的原因。关键词：     

Nd1.67Sr0.33NiO4中的热导反常

报道了两个典型掺杂的镍氧化物Nd＿2-xSr＿xNiO＿4(x =0.33,1.35)的低温热导率、电阻率和低场交流磁化率,测试温区为77—300K. 在Nd＿2-xSr＿xNiO＿4 (x=0.33)样品的热导率-温度曲线上在电荷有序转 变温度（T＿CO）和自旋有序转变温度（T＿SO）附近分别观测到反常, 电荷有序使热导率在T＿CO以下有所增加,反铁磁自旋有序使热导率在T＿SO附近被压制. 在低场交流磁化率-温度曲线上也分别观测到对电荷有序和自旋有 序的响应,而在其电阻率-温度曲线上仅观测到电荷有序. 作为比较,Nd＿1.67Sr0.33NiO＿4样品中没有观测到输运性质和磁性质上的反常. 两个样品中声子热导占 主导地位. Nd＿1.67Sr0.33NiO＿4样品中电荷有序和自旋有序导致的热导 率的反常表明样品中存在强的电荷-声子和自旋-声子相互作用. 关键词：热导率电荷有序自旋有序     

氧掺杂La2CuO4的热导

实验研究了氧掺杂的La2CuO4样品从330K经过慢速冷却和快速冷却后其热导率随温度的变化关系,测量温区为77－300K,在120K以下,两种情况下测得的热导率都随温度的升高而降低。热导率值相同,在120K附近达到极小,120K以上热导率随温度的升高而升高。但经过慢速冷却过程测得的热导值明显低于经过快速冷却过程测得的热导值,分析认为这与两种情况下样品中不同的无序磁散射有关。     

Mn位W掺杂对La0.3Ca0.7MnO3体系磁结构的影响

通过对La_0.3Ca_0.7Mn_1-xW_xO₃(x=0.00,0.04,0.08,0.12,0.15)多晶样品M-T曲线、M-H曲线及ESR谱的测量,研究了Mn位W掺杂对电荷有序体系La_0.3Ca_0.7MnO₃磁结构的影响.结果表明,当掺杂量为0.00≤x≤0.08时,体系存在电荷有序(CO)相,AFM/CO态共存于相变温度以下,电荷有序温度T_CO随着W掺杂量的增加而增加;x＝0.04时,样品在低温下为FM相与AFM/CO相共存,在CO相建立前、后均有FM从PM中分离出来;当x≥0.12时,CO态融化,在极低温度下存在顺磁-铁磁(PM-FM)相变.关键词：磁结构电荷有序融化Mn位掺杂     

一种具有“1111”型结构的新型稀磁半导体(La1–xSrx)(Zn1–xMnx)SbO

利用高温固相反应法,成功合成了一种新型块状稀磁半导体(La_1–xSr_x)(Zn_1–xMn_x)Sb O(x=0.025, 0.05,0.075, 0.1).通过(La³⁺, Sr²⁺)、(Zn²⁺, Mn²⁺)替换,在半导体材料La Zn Sb O中分别引入了载流子与局域磁矩.在各掺杂浓度的样品中均可观察到铁磁有序相转变,当掺杂浓度x=0.1时,其居里温度Tc达到了27.1 K,2 K下测量获得的等温磁化曲线表明其矫顽力为5000 Oe.(La_1–xSr_x)(Zn_1–xMn_x)Sb O与\"1111\"型铁基超导体母体LaFeAsO、\"1111\"型反铁磁体LaMnAsO具有相同的晶体结构,且晶格参数差异很小,为制备多功能异质结器件提供了可能的材料选择.     

成分调制的La1－xSrxMnO3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SrTiO_３单晶衬底上制备出三明治结构为La_0.7Sr_0.3MnO３(100nm)/La_0.96Sr_0.04MnO_３ (5nm)/ La0.7Sr_0.3MnO_３ (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Ir_２２Mn_７８(15n m)/Ni_７９Fe_２１(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L a_１-xSr_xMnO_３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,La_１-xSr_xMnO_３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La_{0.7Sr0.3MnO３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.关键词：１-x}Sr_xMnO_３')\" href=\"#\">La_１-xSr_xMnO_３半金属成分调制复合磁性隧道 结隧穿磁电阻     

Hg0.9Tl0.2Ba2Ca2Cu3O8+δ在磁场下的热导

实验研究了高温超导体Hg09Tl02Ba2Ca2Cu3O8+δ的低温热导率与温度和磁场的关系,测量温度为7—20K,外加磁场为0—6T.结果表明,在不同外场下,超导体的热导率在实验温区内随温度的增加均单调增加;在固定的温度下外加磁场使超导体的热导率减小,并随外磁场的增加达到一个稳定值;热导的相对变化率κ(H)/κ(0)与磁场的关系以及热导率达到稳定值的磁场与测量温度有关.分析讨论了超导体中正常态电子在磁场下受磁通涡旋散射产生附加的热阻关键词：     

SrTiO3的外延覆盖对La0.67Ca0.33MnO3/NdGaO3（001）薄膜中电荷有序相调控的影响

具有各向异性外延应变的La0.67Ca0.33MnO3/NdGaO3(001)外延薄膜,经过高温后退火处理可以诱导出电荷有序相,而外延应力场对电荷有序相的诱导机理有待进一步阐明.本文中,我们在La0.67Ca0.33MnO3薄膜上进一步外延SrTiO3覆盖层,以期从不同方面改变薄膜的应变状态.我们发现薄膜上方的应力钳制可改变来自衬底的各向异性应变,从而明显减弱薄膜中的电荷有序相.因此,除衬底外,外延覆盖层同样也可影响薄膜的应变状态、结构和物性.     

半掺杂Sm0.5Ca0.5MnO3体系的电荷有序和再入型自旋玻璃行为

研究了半掺杂锰氧化物Sm_0.5Ca_0.5MnO₃体系的结构、输运和磁特性,结果表明,在半掺杂情况下,该体系呈现O′类正交结构,表明体系存在典型的Jahn-Teller效应畸变;输运结果在整个测量温区均呈现半导体导电行为,没有出现金属－绝缘体(M-I)转变和CMR效应;电荷有序转变发生在T=270K左右,反铁磁转变温度出现在200K附近,且表现出典型的再入型自旋玻璃(spin-glass)行为,自旋玻璃转变温度T_SG在4关键词：自旋玻璃电荷有序负磁化现象多相竞争     

Spin, charge, and orbital orderings in iron-based superconductors

In this article, we briefly review spin, charge, and orbital orderings in iron-based superconductors, as well as the multi-orbital models. The interplay of spin, charge, and orbital orderings is a key to understand the high temperature superconductivity. As an illustration, we use the two-orbital model to show the spin and charge orderings in iron-based superconductors based on the mean-field approximation in real space. The typical spin and charge orderings are shown by choosing appropriate parameters, which are in good agreement with experiments. We also show the effect of Fe vacancies, which can introduce the nematic phase and interesting magnetic ground states. The orbital ordering is also discussed in iron-based superconductors. It is found that disorder may play a role to produce the superconductivity.     

Nd_(1.67)Sr_(0.33)NiO_4中的热导反常

报道了两个典型掺杂的镍氧化物Nd2 -xSrxNiO4 (x=0 33,1 35 )的低温热导率、电阻率和低场交流磁化率 ,测试温区为 77— 30 0K .在Nd2 -xSrxNiO4 (x=0 33)样品的热导率_温度曲线上在电荷有序转变温度 (TCO)和自旋有序转变温度 (TSO)附近分别观测到反常 ,电荷有序使热导率在TCO 以下有所增加 ,反铁磁自旋有序使热导率在TSO 附近被压制 .在低场交流磁化率_温度曲线上也分别观测到对电荷有序和自旋有序的响应 ,而在其电阻率_温度曲线上仅观测到电荷有序 .作为比较 ,Nd0 6 5Sr1 35NiO4 样品中没有观测到输运性质和磁性质上的反常 .两个样品中声子热导占主导地位 .Nd1 6 7Sr0 33NiO4 样品中电荷有序和自旋有序导致的热导率的反常表明样品中存在强的电荷_声子和自旋_声子相互作用     

Charge order and spin order in Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system

Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melt- ing of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-T curves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.     

Charge order and spin order in Nd0.5Sr0.5Mn1? x (Ga x , Ti x )O3 system

Magnetic properties of Nd0.5Sr0.5Mn1-x(Gax,Tix)O3 system (0.04≤x≤0.4) were investigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melting of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-Tcurves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.     

Influence of the interplay between helicoidal magnetic ordering and superconductivity on the differential conductance in HoNi<Subscript>2</Subscript>B<Subscript>2</Subscript>C/Ag junctions

The point contact spectra of magnetic superconductor HoNi₂B₂C/Ag-based junctions is analysed in the framework of Blonder-Tinkham-Klapwijk (BTK) theory. The anomalous behavior in the dI/dV curves above the Neel temperature(T _N ∼ 5 K) is attempted to be explained by the partial suppression of superconducting gap parameter of the prevailing helical incommensurate structure     

Verwey相变处Fe3O4的结构、磁性和电输运特性

作为典型的金属–绝缘体转变,Fe3O4的Verwey相变蕴涵的丰富物理现象与微观机制,因而受到了人们的广泛关注.在Verwey相变处,Fe3O4的晶体结构、电子结构以及磁各向异性等均发生转变,但其磁基态并未发生改变.与其他强关联体系相比,Fe3O4的Verwey相变不需要考虑磁交换耦合作用的变化,有利于揭示强关联体系中金属–绝缘体转变的物理本质.本文从晶体结构、电荷有序、电输运特性、磁性和铁电特性等方面简要地介绍了Fe3O4的Verwey相变的研究历史和现状.