La_(0.4)Ca_(0.6)MnO_3中Mn-位Fe和Cr掺杂对磁性质的影响

研究了Fe和Cr掺杂对La0.4Ca0.6Mn O3中电荷有序反铁磁基态的调控作用.磁性质的测量结果表明,两种离子掺杂均能有效抑制原型样品中的长程电荷有序相,但是Fe离子掺杂样品均具有反铁磁的基态,而Cr掺杂样品中则出现了显著的铁磁性.结合电输运测量结果显示,Cr掺杂引起的铁磁态同时具有金属性,表明其中是电子双交换作用占主导.对比两种掺杂离子的电子结构发现,Cr离子空的e g电子轨道促进了电子双交换作用,而Fe掺杂则只是引入了不同的自旋交换作用,导致自旋无序.     

钙钛矿型锰氧化物(La$lt;sub$gt;0.8$lt;/sub$gt;Eu$lt;sub$gt;0.2$lt;/sub$gt;)$lt;sub$gt;4/3$lt;/sub$gt;Sr$lt;sub$gt;5/3$lt;/sub$gt;Mn$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;7$lt;/sub$gt;的磁性和电性研究

采用传统固相反应法制备钙钛矿型锰氧化物 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇多晶样品, X-射线衍射分析表明, 样品(La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇结构呈现良好的单相. 通过磁化强度随温度的变化曲线(M-T)、不同温度下磁化强度随磁场的变化曲线(M-H)和电子自旋共振谱发现: 在300 K以下, 随着温度的降低, 样品先后经历了二维短程铁磁有序转变 (T_C^2D ≈ 282 K)、三维长程铁磁有序转变(T_C^3D ≈ 259 K)、奈尔转变(T_N ≈ 208K)和电荷有序转变(T_CO ≈ 35 K); 样品 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇在T_N以下, 主要处于反铁磁态; 在T_C^3D达到370 K时, 样品处于铁磁-顺磁共存态, 在370 K以上时样品进入顺磁态. 此外, 分析电阻率随温度的变化曲线(ρ-T)得到: 样品在金属-绝缘转变温度(T_P ≈ 80 K)附近出现最大磁电阻值, 其位置远离T_C^3D, 表现出非本征磁电阻现象, 其磁电阻值约为61%. 在T_CO以下, 电阻率出现明显增长, 这是由于温度下降使原本在高温部分巡游的e_g电子开始自发局域化增强所致. 通过对 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇的ρ-T 曲线拟合, 发现样品在高温部分的导电方式基本遵循小极化子的导电方式. 关键词： 磁性 电性 金属-绝缘转变温度 电子自旋共振     

La0.4Ca0.6MnO3系统中Mn位Fe和Cr掺杂效应的比较性研究

利用固相反应法制备了Mn位Fe³⁺和Cr³⁺掺杂的系列锰氧化物La_0.4Ca_0.6(Mn_1-x(y)B_x(y))O₃ (B=Fe³⁺ (0≤x≤0.1); Cr³⁺ (0≤y≤0.1)) 多晶样品,研究了掺杂对样品输运性质的影响.实验结果表明两种离子具有截 关键词： 锰氧化物 反铁磁 磁电阻效应     

点接触金属/Pr$lt;sub$gt;0.7$lt;/sub$gt;Ca$lt;sub$gt;0.3$lt;/sub$gt;MnO$lt;sub$gt;3$lt;/sub$gt;/Pt结构稳定的低电流电阻开关特性

利用自主开发的导电原子力显微镜控制Pt,W探针构成点接触金属/Pr_0.7Ca_0.3MnO₃（PCMO）/Pt三明治结构,对其电流-电压（I-V）及脉冲诱导电阻开关（EPIR）特性进行了研究.研究发现,在10 nA限流下两种电极对应结构的I-V都表现出相当稳定的双极性电阻开关特性,以及大于100的电阻开关比.进一步测试发现,点接触W/PCMO/Pt器件具有在10 nA限流下稳定的EPIR特性以及100 pA限流下重复的双极性电阻开关特性.此电流比已报道的电流低3个数量级,表明此结构在低功耗存储器件方面的潜在应用.通过对比样品不同位置、不同限流、不同接触面积点接触Pt/PCMO/Pt的I-V回滞特性,把点接触器件在低电流下稳定、显著的电阻开关效应归结于小的器件面积导致强的局域电场加强了O离子迁移效应. 关键词： 脉冲诱导电阻开关 电场下氧离子迁移 电阻开关     

Co掺杂对Mn$lt;sub$gt;3$lt;/sub$gt;Sn$lt;sub$gt;1-$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;Co$lt;sub$gt;$lt;em$gt;x$lt;/em$gt;$lt;/sub$gt;C$lt;sub$gt;1.1$lt;/sub$gt;化合物的磁性质、熵变以及磁卡效应的影响

利用固态反应法制备了Mn₃Sn_1-xCo_xC_1.1 （x=0.05,0.1,0.2） 系列化合物,研究了Co掺杂对其磁性质、相变、熵变的影响. 随着Co掺杂量的增加,样品的居里温度由283 K先降到212 K （Mn₃Sn_0.9Co_0.1C_1.1） 后又升到332 K （Mn₃Sn_0.2Co_0.8C_1.1）,相变类型由一级相变逐渐转变为二级相变. 增大Co的掺杂量,Mn₃Sn_1-xCo_xC_1.1化合物的熵变峰值逐渐减小,磁熵变温区由9 K展宽到300 K. 当Co掺杂量为0.2时,相对制冷量达到最高,为103 J/kg （磁场强度为1.6 MA/m）. 由于室温附近良好的磁致冷效应,该类材料在磁制冷领域可能具有重要的应用前景. 关键词： 磁性质 相变 磁卡效应 相对制冷量     

Sr位Nd掺杂对SrBi$lt;sub$gt;2$lt;/sub$gt;Nb$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;9$lt;/sub$gt;性能的影响及机理研究

采用传统固相法制备了（Sr_1-3x/2A_x/2Nd_x）Bi₂Nb₂O₉（x=0,0.05,0.1和0.2）陶瓷,并系统研究了Nd离子取代Sr离子对SrBi₂Nb₂O₉性能的影响及其作用机理.研究结果表明：Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的介电常数和介电损耗随温度变化的行为具有明显的离子松弛极化特征.Nd³⁺对Sr²⁺的部分取代,导致Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉剩余极化强度P_r稍有下降,但其压电系数d₃₃却有所增加,根据铁电热力学理论,这是Nd³⁺对Sr²⁺取代导致材料介电常数增大所致.Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的居里温度（T_C）没有随Nd含量的增加而变化,拉曼光谱技术分析表明这是其NbO₆八面体畸变程度没有发生变化所致.Nd³⁺取代Sr²⁺提高了材料的介电常数ε_r、压电系数d₃₃、机电耦合系数K_p,同时降低了机械品质因数Q_m,但是谐振频率温度系数C值没有改变. 关键词： 压电陶瓷 介电性能 压电性能 拉曼光谱     

笼状Au$lt;sub$gt;20$lt;/sub$gt;内掺$lt;i$gt;M$lt;/i$gt;$lt;sub$gt;13$lt;/sub$gt;($lt;i$gt;M$lt;/i$gt;=Fe，Ti)团簇磁性的密度泛函计算研究

采用密度泛函理论中的广义梯度近似方法,对M₁₃（M=Fe,Ti）以及M₁₃内掺Au₂₀团簇的几何结构和磁性进行了计算研究.结果表明：M₁₃和M₁₃内掺Au₂₀团簇的几何结构在0.006—0.05 nm误差范围内保持着I_h对称性.Fe₁₃团簇最低能态的总磁矩为44 μ_B,内掺到Au₂₀笼中后形成的Fe₁₃内掺Au₂₀团簇的最低能态总磁矩为38 μ_B,且Au原子与内掺Fe₁₃团簇之间存在着弱铁磁相互作用.Ti₁₃团簇在总磁矩为6 μ_B时能量最低,掺入Au₂₀笼后形成的Ti₁₃内掺Au₂₀团簇最低能态总磁矩是4 μ_B,内表面12个Ti原子与表面Au壳之间是弱铁磁相互作用,而与中心Ti原子之间是弱反铁磁相互作用.由于Au₂₀笼状外壳的影响,Fe₁₃内掺Au₂₀和Ti₁₃内掺Au₂₀团簇中Fe₁₃和Ti₁₃的磁矩比无金壳的Fe₁₃和Ti₁₃团簇的磁矩分别减少了6.81 μ_B和2.88 μ_B. 关键词： 几何结构 磁性 密度泛函理论     

Ca$lt;sub$gt;0.64$lt;/sub$gt;WO$lt;sub$gt;4$lt;/sub$gt;:Eu$lt;sub$gt;0.24$lt;/sub$gt;陶瓷的高温相变机理及其对发光性能的影响

纯的CaWO₄具有优异的耐压、耐热稳定性,化学组成为Ca_0.64WO₄:Eu_0.24的陶瓷也具有CaWO₄结构,但Ca²⁺晶格位置含有12 mol%的肖特基缺陷. 这种缺陷浓度高的CaWO₄ 相是否具有良好的高温稳定性还有待研究. 本文探讨了过度烧结对Ca_0.64WO₄:Eu_0.24陶瓷相结构的影响,揭示了在高温下产生相变的可能原因,并研究了该相变对材料发光性能的影响. 研究表明,当烧结温度超过1100 ℃时,被肖特基缺陷束缚的部分氧离子会解离,造成Ca_0.64WO₄:Eu_0.24陶瓷体相中氧元素含量严重不足,诱发CaWO₄相发生相变,析出单斜晶系的Eu₂WO₆;研究还发现,CaWO₄相的晶面间距在高温相变后会增大;这可能是导致Ca_0.64WO₄:Eu_0.24陶瓷发光强度显著降低的一个重要原因. 关键词： 相变 钨酸钙 铕 发光     

Tb$lt;sub$gt;0.3$lt;/sub$gt;Dy$lt;sub$gt;0.6$lt;/sub$gt;Pr$lt;sub$gt;0.1$lt;/sub$gt;(Fe$lt;sub$gt;1-$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;Al$lt;sub$gt;$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;)$lt;sub$gt;1.95$lt;/sub$gt;合金的磁性、磁致伸缩和穆斯堡尔谱研究

系统研究了室温下Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95 （x=0.05,0.1,0.15,0.2,0.25,0.3）合金中元素Al替代Fe对结构、磁性、磁致伸缩性能和自旋重取向的影响.测量结果发现,x<0.2时Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95合金基本上是纯的单相,x=0.2时出现其他杂相,杂相随Al替代量的增加不断增多.随Al替代量x的增加,点阵常数a接近于线性增大,Curie温度T_C逐渐下降,而矫顽力H_c急剧下降.振动样品磁强计（VSM）测量发现,磁化强度M随Al替代量x的变化较为复杂.VSM计和磁致伸缩效应测量共同表明,少量Al的替代有利于降低磁晶各向异性,而且随着Al替代量x的增多磁致伸缩系数快速减小,x>0.15时巨磁致伸缩效应消失.穆斯堡尔效应研究发现,随Al含量的增加Tb_0.3Dy_0.6Pr_0.1（Fe_1-xAl_x）_1.95合金中易磁化轴可能在{110}面逐渐偏离了立方晶体的主对称轴,发生自旋重取向,从而引起合金宏观磁性、磁致伸缩性能的变化. 关键词： 磁致伸缩 立方Laves相 自旋重取向 穆斯堡尔谱     

相位物体$lt;i$gt;Z$lt;/i$gt;-扫描研究金属簇合物［$lt;i$gt;Tp$lt;/i$gt;*W($lt;i$gt;μ$lt;/i$gt;$lt;sub$gt;3$lt;/sub$gt;-S)$lt;sub$gt;3$lt;/sub$gt;Cu$lt;sub$gt;3$lt;/sub$gt;$lt;i$gt;Py$lt;/i$gt;$lt;sub$gt;3$lt;/sub$gt;($lt;i$gt;μ$lt;/i$gt;$lt;sub$gt;3$lt;/sub$gt;-Br)］($lt;i$gt;PF$lt;/i$gt;$lt;sub$gt;6$lt;/sub$gt;)/DMF溶液的瞬态热致非线性折射

在纳秒时域,采用相位物体（PO）Z-扫描技术研究了一种新型金属簇合物溶液的瞬态热致非线性效应.该方法的最大优点是很容易区分瞬态热致非线性折射和三阶非线性折射.本文利用PO Z-扫描和传统Z-扫描研究了在8 ns脉宽、不同能量激光脉冲作用下［Tp*W（μ₃-S）₃Cu₃Py₃（μ₃-Br）］（PF₆）/DMF溶液的光学非线性.从声波方程和热传导方程出发,对实验结果进行了理论分析和数值模拟,理论值和实验结果很好的吻合.研究结果表明,样品溶液的非线性折射主要来源于瞬态热致非线性效应. 关键词： Z-扫描')" href="#">相位物体 Z-扫描 瞬态热致非线性折射 光克尔效应 DMF     

A-site disorder effects in electron-doped manganite La0.4Ca0.6MnO3

The A-site disorder effects on the stability of charge-ordered state in electron-doped manganite R_0.4A_0.6MnO₃ (where R = La, Pr, Nd, Sm, and A = Ca, Sr, Ba) are investigated by detailed measurements of transport, magnetism, and specific heat. The robust charge-ordered phase within the prototype sample can be successively suppressed by enhancing the A-site disorder, and finally an atomic-scale spin-glass state is evidenced in the highest disordered sample. However, no ferromagnetic phase can be observed; even the long-range charge-ordered antiferromagnetic phase is fully suppressed, which can be associated with the insufficient e _g electron density in such an electron-doped manganite. This revealing is helpful for understanding the origin of ferromagnetic phase in nano-sized or B-site doped charge-ordered manganites with small e _g electron density.     

Pico-second photoelectric characteristic in manganite oxide La0.67Ca0.33MnO3 films

Ultrafast photoelectric characteristic has been observed in La_0.67Ca_0.33MnO₃ films on tilted SrTiO₃ substrates. A pico-second (ps) open-circuit photovoltage of the perovskite manganese oxide films has been obtained when the films were irradiated by a 1.064μm laser pulse of 25 ps duration. The rise time and full width at half-maximum of the photovoltage pulse are ～300 ps and ～700 ps, respectively. The photovoltaic sensitivity was as large as ～500 mV/mJ.     

Magnetotransport properties of La0.67Ca0.33MnO3//La0.67Sr0.33MnO3 bilayers

The perovskite bilayers La0.67Ca0.33MnO3 （LCMO） （100 nm） / La0.67Sr0.33MnO3（LSMO） （100 nm） and LSMO （100 nm） / LCMO （100 nm） are fabricated by a facing-target sputtering technique. Their transport and magnetic properties are investigated. It is found that the transport properties between them are different obviously due to distinguishable structures, and the different lattice strains in both films result in the difference of metal-to-insulator transition. Only single-step magnetization loop appears in our bilayers from 5K to 320K, and the coercive force of LSMO/LCMO varies irregularly with a minimum ～ 2387A/m which is lower than that of LCMO and LSMO single layer films. The behaviour is explained by some magnetic coupling.     

Ultra-sharp metamagnetic transition in manganite Pr0.6Na0.4MnO3

We report the magnetic and electrical transport properties of manganite Pr_0.6Na_0.4MnO₃. At the temperature of 2 K, a field-induced steplike magnetization and resistivity transition are observed. The step transitions of magnetization and resistivity are shifted to higher fields as a result of field cooling, and transformed to a smooth broad one when the cooling field is higher than 20 kOe. Moreover, in a magnetic field slightly below the critical field, the magnetic and resistive relaxation exhibits a spontaneous step after a long incubation time when both the temperature and magnetic field are constant. Such steplike transitions are discussed in terms of a martensiticlike transformation associated with phase separation.     

Effect of Cr doping on the magnetic and electrical transport properties of charge-ordered Bi0.5Ca0.5MnO3

An experimental study on the magnetic and electrical transport properties of the manganites Bi_0.5Ca_0.5Mn_1−xCr_xO₃ (BCMCO) (0≤x≤0.12) is carried out. The results show that Cr doping can suppress the charge-ordering transition, favoring the ferromagnetic clusters. For x=0.12, the charge-ordering transition disappears but a very broad paramagnetic-ferromagnetic-like transition is detected at the Curie temperature T_C=72.6 K. It is caused by phase separation or coexistence of the charge-ordering and ferromagnetic phase. Moreover, the critical Cr content to destroy charge ordering phase in BCMCO does not match the general monotonous tendencies shown by Cr-doped Re_0.5Ca_0.5MnO₃ (Re-rare-earth). These differences are ascribed to the fact that the ground state in BCMCO differs markedly from the ferromagnetic metallic phase in Cr-doped Re_0.5Ca_0.5MnO₃ compounds.     

Electron spin resonance study of Fe doping effect in La0.67Ca0.33MnO3

Electron spin resonance (ESR) study was carried out on La_0.67Ca_0.33Mn_1−xFe_xO₃ (x=0.0, 0.04) samples. The temperature dependence of the ESR spectra indicates the presence of phase separation above and below T_C in x=0.0 and 0.04 sample, respectively. The increase of the g-value in the high-temperature region indicates the existence of local spin correlations even in the paramagnetic state. The activation energy obtained from both the temperature dependence of the ESR intensity and linewidth exhibits a smaller value in the Fe-doped sample. Our study suggests that the ferromagnetic spin correlations would be significantly weakened by a slight doping of Fe ions on Mn sites.     

The current-induced effect on the Jahn-Teller distortion in the La0.5Ca0.5MnO3 manganite

The influence of dc current on the resistivity ρ and the Young's modulus E of La_0.5Ca_0.5MnO₃ compound has been investigated by means of an in situ measuring method. At low temperatures, both the resistivity ρ and the relative modulus ΔE increase with the current. A relaxation behavior of ρ to the higher resistive state is observed at a fixed temperature and a constant current. After storing the sample for a few days, ρ decreases with the current, accompanying a slight drop of ΔE at low temperatures. Current-induced effects on ρ and ΔE are interpreted according to the current-induced interwinning of Mn³⁺O₆ octahedral distortion modes between Q₂- and Q₃-types, which is suggested to contribute to the variation of the resistivity.     

CURRENT-DEPENDENT POSITIVE MAGNETORESISTANCE IN Ga-DOPED La0.5Ca0.5MnO3

The magnetic and transport properties of the Ga-doped charge-ordering state La_0.5Ca_0.5MnO₃ have been studied. A current-dependent large positive magnetoresistance (1080%) at 5 K was observed. These observations are interpreted in terms of the spin-dependent tunnelling process between ferromagnetic clusters embedded in an antiferromagnetic matrix.     

La0.67Ca0.33MnO3薄膜皮秒光电效应

在1064 nm波长脉冲激光（脉宽25 ps）的照射下，钙钛矿氧化物薄膜La0.67Ca0.33MnO3/SrTiO3具有超快光电效应，对激光脉冲显示ps量级的响应时间，上升沿响应时间300 ps，半高宽700 ps，同时，对激光能量的响应灵敏度为500 mV/mJ。