共查询到20条相似文献,搜索用时 78 毫秒
1.
系统研究了衬底为SrTiO3和LaAlO3上的La0.67Ca0.33MnO3薄膜中的矫顽力随厚度和应变的变化。结构分析表明薄膜为(001)方向织构,而且薄膜中的晶粒尺寸随着薄膜厚度的减小而减小。磁测量表明矫顽力先随着膜厚的减小而增加,在t=10-25nm附近到达一极大值。随后,矫顽力随厚度的减小而降低。还得出矫顽力的大小与测量方向有关:t≥25nm (t≤10nm)时,难磁化方向的矫顽力大于(小于)易磁化方向的矫顽力。据此,我们提出:在厚膜(t≥25nm)中,矫顽力变化由畴壁钉扎机制决定;在超薄膜(t≤10nm)中,则与磁畴的形核机制有关。根据t= 5、10、25、400nm的LCMO/STO薄膜的初始磁化曲线,以及t=5,50nm的LCMO/LAO薄膜的小磁滞回线的测量,我们对薄膜中矫顽力机制作了验证,并且还讨论了钉扎和形核机制发生的非均匀区的尺寸。 相似文献
2.
在厚度为25—400nm范围内,系统地研究了 (001)SrTiO_3(STO), (001)LaAlO_3(LAO)衬底上La_0.67Ca_0.33Mn_O.3 (LCMO)薄膜的电输运与居里温度T_C随薄膜厚度及衬底的变化. 结果表明,随薄膜变薄,电阻率ρ增加,T_C降低. 对于同一薄膜厚度,LCMO/STO薄膜的ρ大于LCMO/LAO基上的薄膜的ρ. T_C衬底的依赖关系则与ρ相反. 分析表明,LCMO薄膜的低温区电阻温度(ρ-T) 符合关系式ρ=ρ_0+Bω_s/sin h^2(ω_s/2/k_BT)+CT^n, 其中ρ_0为剩余电阻;等号右端第二项反映软光学模声子对电子散射的贡献;第三项包括其余可能散射机 理在电输运过程中所起的作用;B,ωs(软光学模声子的平均频率)与C都为拟合系数. 高温区的电输运则由小极化子跃迁模型ρ=DT×exp(E_a/k_BT)描述(E_a为极化子激 发能). 根据ρ_0,ωs,E_a以及T_C变化,初步讨论了薄膜中的厚度与应变效应. 进一步 研究发现ωs,E_a的变化与T_C相关,从而说明极化子效应为影响T_C变化的主要因素.
关键词:
锰氧化物薄膜
电输运
居里温度
极化子 相似文献
3.
4.
采用激光分子束外延技术,在玻璃衬底上制备了La067Sr033MnO3 (LSMO) 薄膜,X射线衍射测量结果表明在玻璃衬底上生长的LSMO薄膜沿c轴择优取向生长.在外磁场3 T和88, 220, 300 K条件下,LSMO薄膜的磁电阻变化率分别达到-378%, -268%和-607%.实验结果表明,在廉价的玻璃衬底上制备大面积和具有应用价值的锰氧化物薄膜是可行的.
关键词:
锰氧化物薄膜
玻璃衬底
外延生长 相似文献
5.
La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3单晶的磁性和磁电阻特性。由于缺少晶粒间界,磁场对于自旋涨落的抑制作用更加明显,所以单晶中的磁电阻率比多晶的提高了两个数量级。通过Fe的掺杂,在40×105A/m的磁场下,磁电阻率从3400%进一步提高到了17600%。通过对居里温度以上电阻率的小极化子模型拟和的结果,我们看到随着Fe的掺杂,激活能被提高。磁极化子激活能的增大可以更加局域电子,这可能是在Fe掺杂单晶中本征磁电阻率进一步提高的主要原因。 相似文献
6.
7.
利用固相反应烧结法制备了La067Pb033MnO3单相多晶样品.研究了其结构、磁性及输运特性.结果表明,样品呈菱面相晶体结构,空间群为R3C,居里温度TC(=353K)非常接近TMI(=360K).在居里温度附近,发生铁磁-顺磁转变,导电特性由金属特征向半导体特征过渡.磁电阻在居里点达到极大值.当H=16T时,磁电阻的极大值为145%;当H=08T时,磁电阻的极大值为9%.输运性质表明,TTMI时
关键词:
磁电阻
输运特性
磁极化子
钙钛石 相似文献
8.
用直流磁控溅射法在(100)LaAlO3衬底上制备了La0.9Sr0.1MnO3薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La0.9Sr0.1MnO3薄膜在281 K处发生金属绝缘体转变.电流在0.01—4 mA范围内,薄膜的峰值电阻率随电流增大而减小,在4 mA下获得了30.5%的峰值电阻率变
关键词:
掺杂锰氧化合物
0.9Sr0.1MnO3薄膜')" href="#">La0.9Sr0.1MnO3薄膜
电流诱导效应
相分离理论 相似文献
9.
利用脉冲激光沉积技术在LaAlO3(00l)单晶衬底上制备了La067Ba033MnO3薄膜,研究了CO2激光辐照对La067Ba033MnO3薄膜的微结构和磁电性能的影响.结果表明,经激光辐照后,La067Ba033MnO3薄膜的结晶性增强,薄膜应变减小;薄膜表面形貌由“岛状”结构变为“平原"结构,且粗糙度大大降低;同时,薄膜的饱和磁化强度、铁磁居里温度、金属—绝缘态转变温度和磁电阻增大,而矫顽场和电阻率减小.根据对传统退火效应的分析和理论计算,认为激光辐照导致的表面微结构的变化以及薄膜的氧含量和均匀性的提高对La067Ba033MnO3薄膜的磁电性能的改善与优化密切相关.
关键词:
庞磁电阻
激光辐照
脉冲激光溅射沉积 相似文献
10.
11.
Mahmoud Aly Hamad 《Phase Transitions》2013,86(1-2):106-112
The dependence of magnetization on the variation of temperature for La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 perovskite-type ceramic materials under an external magnetic field was modelled. Application of phenomenological model was performed, showing a good agreement with the experimental data. Temperature dependence of change of both magnetic entropy and specific heat under magnetic field 0.05?T was predicted for La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3. Predicted values of maximum magnetic entropy change, full-width at half-maximum, relative cooling power and maximum specific heat under 0.05 T were evaluated. 相似文献
12.
La0.67Sr0.33MnO3薄膜光响应特性研究 总被引:2,自引:0,他引:2
实验测量了在不同温度和电场下,超巨磁电阻CMR(colossal magnetoresistance)薄膜材料La0.67Sr0.33MnO3(LSMO)的光响应特性.发现样品被激光照射后,具有光诱导电阻变化的特性.在温度小于居里点Tc时,电阻随温度升高而增大,在Tc以上时,电阻则随温度升高而减小.通过对样品的光脉冲响应和偏置电场的关系分析,可认为其光响应特性的机理与激光激励下引起的自旋系统变化有关. 相似文献
13.
通过实验研究了La0.67-xGdxSr0.33CoO3、La0.67-xGdxSr0.33MnO3(x=0.00、0.05、0.10、0.20、0.30、0.40、0.50、0.60、0.67)体系的磁化强度与温度的关系(M~T)曲线、磁化强度与磁场强度的关系(M~H)曲线.实验结果表明,随Gd掺杂浓度增高,La0.67-xGdxSr0.33CoO3体系的磁结构表现为团簇玻璃态,x>0.10样品的M~T曲线出现了低温区M值急剧上升的奇特现象;La0.67-xGdxSr0.33MnO3体系的磁结构从长程铁磁有序向团簇玻璃态、反铁磁状态转变,x≥0.50样品的M~T曲线在低温区急剧下降.两种体系呈现的不同现象,来源于Gd与Co、Mn不同的耦合作用和Co的自旋态的转变. 相似文献
14.
Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
15.
M Pattabiraman P Murugaraj G Rangarajan V Prasad S V Subramanyam V S Sastry Sang-Mo Koo K V Rao 《Pramana》2000,55(3):455-469
Annealing dependence of the lattice parameter, resistivity, magnetoresistance and thermopower have been studied on Nd0.7-Sr0.33MnO3 thin films deposited on LaAlO3 and alumina substrates by pulsed laser ablation. Upon annealing at 800°C and 1000°C the lattice constant of the LaAlO3 film tends toward that of the bulk target due to reduction in oxygen vacancies. This results in a metal-insulator transition
at temperatures which increase with progressive annealing along with a decrease in the observed low temperature MR. Using
a magnon scattering model we estimate the e
g bandwidth of the film annealed at 1000°C and show that the magnon contribution to the resistivity is suppressed in a highly
oxygen deficient film and gains prominence only upon subsequent annealing. We also show that upon annealing, the polaron concentration
and the spin cluster size increases in the paramagnetic phase, using an adiabatic polaron hopping model which takes into account
an exchange dependent activation energy above the resistivity peak. 相似文献
16.
《Current Applied Physics》2018,18(11):1320-1326
High crystalline quality CrN thin films have been grown on La0.67Sr0.33MnO3 (LSMO) templates by molecular beam epitaxy. The structure and magnetic properties of CrN/LSMO heterojunctions are investigated combining with the experiments and the first-principles simulation. The Nėel temperature of the CrN/LSMO samples is found to be 281 K and the saturation magnetization of CrN/LSMO increases compared to that of LSMO templates. The magnetic property of CrN/LSMO heterostructures mainly comes from Cr atoms of (001) CrN and Mn atoms of (001) LSMO. The (001) LSMO induces and couples the spin of the CrN sublattice at CrN/LSMO interface. 相似文献
17.
Strain-induced insulator–metal transition in ferroelectric BaTiO_3(001) surface:First-principles study
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The electronic properties of TiO_2-terminated BaTiO_3(001) surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator–metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO_3(001) surface. 相似文献
18.
Previous infrared studies on the hole-doped manganite La0.67Sr0.33MnO3 (LSMO) have analysed its charge dynamics in terms of one type of charge carrier despite evidence of both electron and hole Fermi surfaces. Here, we investigate the charge dynamics of an LSMO film with infrared and optical spectroscopy in order to provide a complete picture of metallic conduction. In the ferromagnetic metallic phase, the low-frequency optical conductivity is best explained by a two-carrier model comprising electrons and holes. The number densities, effective masses and relaxation response of the delocalized electrons and holes are quantified. We discover that only one-third of the doped charges are coherent and contribute to the dc transport. Metallic LSMO cannot be classified as a bad metal at low temperatures because the mean free path of the coherent, mobile charge carriers exceeds the Ioffe–Regel–Mott limit. The incoherent spectral response of the doped charges manifests itself as a broad mid-infrared feature. We also report the first observation of splitting of an infrared-active phonon due to local Jahn–Teller distortion in the vicinity of the thermally driven transition to the nonmetallic, paramagnetic phase in LSMO. This demonstrates that infrared spectroscopy is capable of detecting the presence of local lattice distortions in correlated electron systems. 相似文献
19.
Z. Song J.I. Pascual H. Conrad K. Horn H.-P. Rust 《Applied Physics A: Materials Science & Processing》2001,72(8):S159-S162
The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed. 相似文献
20.
The structure, electrical resistivity, and magnetoresistance of predominantly oriented La0.67Ca0.33MnO3(30 nm)/LaAlO3 films are investigated after partial relaxation of biaxial mechanical stresses. The negative magnetoresistance MR of the films reaches a maximum at T = 235–240 K. The full width at half-maximum of the peak in the curve MR(T) for a film is five to six times greater than that for a manganite layer grown on a substrate with a small lattice mismatch. For T < 150 K, the temperature dependence of the electrical resistivity ρ of the films is fitted well by the relationship ρ = ρ0 + ρ1 (H)T 4.5, where ρ0 ≡ ρ(T = 4.2 K) and ρ1(H) is a parameter that is independent of temperature but dependent on the magnetic field H. The parameter ρ1(H = 0) for the La0.67Ca0.33MnO3(30 nm)/LaAlO3 films is several times larger than that for thin manganite layers only weakly strained by the substrate. The electrical resistivity ρ1 decreases almost linear as the quantity μ0 H increases in the field range 1–5 T. 相似文献