La0.67-xSmxSr0.33MnO3(0.40≤x≤0.60)体系的TCR研究

通过测量La0.67-xSmxSr0.33MnO3(x=0.40,0.50,0.60)体系的M～T曲线和ρ～T曲线,研究了La位Sm掺杂对体系电阻温度系数 (TCR)的影响.实验结果表明:Sm掺杂引起的电阻率曲线急剧变化,导致大的TCR出现;TCR在x=0.40时出现峰值,随Sm掺杂的增加,TCR值逐渐减小.体系出现大的TCR,来源于Sm掺杂引起的晶格畸变和额外磁性.     

Transport effects in La0.67−x R x Sr0.33MnO3 (R=Eu, Gd)

An experimental study is reported on the temperature dependences of the magnetic susceptibility, electrical resistivity, magnetoresistance, thermo-and magnetothermopower, and on the Hall effect of the polycrystalline lanthanum manganites La_0.67?x R _x Sr_0.33MnO₃ (x=0 and 0.07, R=Eu, Gd) within the 77-to 430-K temperature range. Replacement of a small amount of lanthanum by europium or gadolinium was found to result in a considerable decrease in the resistivity and in a change in the pattern of its temperature dependence. The temperature dependence of both the ordinary and anomalous Hall coefficients near the Curie temperature is shown to be determined by the change in the number of carriers in delocalized states. A method is proposed for separation of the hole and electronic contributions to thermopower in the ferromagnetic region. The conduction mechanisms are discussed in terms of the concept of mobility edge motion.     

La0.67Ca0.33Mn1-xCrxO3(0.0≤x≤0.15)中异常的CMR效应

我们研究了Mn位掺Cr体系La0.67Ca0.33Mn1-xCrxO3（0．0≤x≤0．15）的磁怀和磁电阻性质,发现Cr掺杂对居里温度Tc影响不明显,但是导致了反常的电输运和磁电阻行为,随着Cr含量的增加,起始电阻率峰向低温移动,同时电阻率出现一个附加峰,在磁场作用下,两个电阻率峰被强烈压缩,导致CMR效应中出现双峰,并且CMR效应的温区被极大地拓宽,从低温直到接近室温,这个结果表明：Mn位元素替代是调节CMR效应的有效方法。     

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.     

Er低掺杂(0.0≤x≤0.20)对La0.67Sr0.33MnO3输运行为的影响

通过测量M-T曲线和ρ-T曲线,研究了Er低掺杂(0.0≤x≤0.20)对La0.67Sr0.33MnO3磁电性质的影响.发现La位被更小的稀土离子Er替代,居里温度Tc和磁化强度M都会降低,这被认为是由于A位离子半径减小导致更大的Mn-O-Mn键的畸变,从而削弱了双交换作用,同时稀土离子的局域磁矩会对体系的物理性质产生作用.在FM相主要是单磁子散射起作用,表现为金属型导电,可以用公式ρ=ρ0 AT2拟合,但在低温下偏离了T2关系, 这是由于Er离子的局域磁矩对载流子散射产生较大贡献的缘故; 在相变温区是PM相的小极化子与FM相的单磁子两种输运性质的共存.     

Kinetic arrest of the first-order to R3c Pbnm phase transition in supercooled La(x)MnO(3+δ) (x = 1 and 0.9)

We report the occurrence of kinetic arrest of the first-order phase transition from R3c to Pbnm in supercooled La(x)MnO(3±δ) (x = 1 and 0.9, i.e. δ > 0.125). Structural studies have been done, employing low temperature transmission electron microscopy (LT-TEM) and low temperature x-ray diffraction (LT-XRD) techniques. No phase transformation was observed even in La(x)MnO(3±δ) aged for ~12 h at 98 K. The evidence of the occurrence of kinetic arrest was realized at low temperatures through in situ electron beam triggered nucleation and perpetual devitrification of the R3c phase into a Pbnm phase. It was clearly evidenced that the R3c structure of La(x)MnO(3±δ), below its ferromagnetic transition temperature, is metastable and prone to be transformed to a Pbnm orthorhombic structure following initiation by an electron beam trigger. The electron beam transformed Pbnm phase was found to transform back to the R3c phase through a first-order phase transition occurring close to the ferromagnetic to paramagnetic transition (T(c)) during heating. The glass-like kinetics of the arrested R3c phase has been investigated through resistance relaxation measurements, showing a decreasing logarithmic rate of decay of the arrested R3c phase towards the stable Pbnm phase with decreasing temperature, down to 5 K. On the basis of the correlations observed in the resistance-versus-temperature, magnetization-versus-temperature, magnetization-versus-field, resistance relaxation and LT-XRD measurements, the occurrence of kinetic arrest has been attributed to the suppression of Jahn-Teller distortion by double exchange across the insulator-metal transition.     

La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3(0.0≤x≤0.15)中异常的CMR效应

我们研究了Mn位掺Cr体系La0 .67Ca0 .33Mn1-xCrxO3( 0 .0≤x≤ 0 .15)的磁性和磁电阻性质 ,发现Cr掺杂对居里温度Tc 影响不明显 ,但是导致了反常的电输运和磁电阻行为 ,随着Cr含量的增加 ,起始电阻率峰向低温移动 ,同时电阻率出现一个附加峰 .在磁场作用下 ,两个电阻率峰被强烈压缩 ,导致CMR效应中出现双峰 ,并且CMR效应的温区被极大地拓宽 ,从低温直到接近室温 .这个结果表明 :Mn位元素替代是调节CMR效应的有效方法 .     

La2/3(Ca1-xMgx)1/3MnO3(0≤x≤60%)系统中不寻常的超大磁电阻

用溶胶-凝胶法并经过1450℃后处理而制备出名义组分为La2/3(Ca1-xMgx)1/3MnO3 (0≤x≤60%)多晶样品.磁化测量表明,除磁转变温度因Mg掺杂而稍有降低外,磁性质整体上和不含Mg样品无本质上的差别.未加磁场下阻温关系测量表明,即使Mg含量高达60%,实验上仍观察到绝缘体到金属的转变.特别有意义的结果是,适当的Mg掺杂可明显提高转变温度附近的磁电阻效应,例如,在Mg掺杂量为30～40%的样品中,1T磁场下观察到的磁电阻甚至比不含Mg样品在5T磁场下得到的值还要大.     

非化学计量配比La0.67Sr0.33-x□x MnO3的结构和输运性质的研究

利用固相反应法制备了非化学计量配比的类钙钛矿锰氧化物La0.67Sr0.33-x□xMnO3(0相似文献   

Electrical transport properties of YCo_(1-x)Mn_xO_3(0 ≤x≤ 0.2)prepared by sol–gel process

Mn substitution compounds YCo1-xMnx O3(0 ≤ x ≤ 0.2) are synthesized by using the sol–gel process. Electrical transport properties of YCo1-xMnx O3 are investigated in the temperature range from 200 K to 780 K. The experimental results show that after Mn substitution the electrical resistivity of YCo1-xMnx O3 first increases, then decreases, which is due to the electrons introduced by Mn doping. The sign of Seebeck coefficient for YCo1-xMnx O3(x = 0) is positive or negative, which is also proved by the Hall coefficient measurement. Moreover, at about room temperature, the Seebeck coefficient of YCo1-xMnx O3 with 1% doping Mn content becomes a negative value, whose absolute value is maximum;furthermore, the absolute value gradually decreases with increasing the Mn substitution content, which can be explained by the double carrier model.     

La0.67Ca0.33MnO3/NdGaO3(001)薄膜中外延应变诱导的各向异性磁阻效应

本文使用脉冲激光沉积方法在正交的NdGaO3(001)衬底上外延生长了La0.67Cao.33MnO3薄膜.退火后,由于外延应变引起薄膜正交畸变增强,薄膜在低于250K的整个温度区间都出现了铁磁金属态和反铁磁绝缘态的相分离和相竞争.这两相的竞争强烈依赖于磁场相对晶轴的方向,由此导致存在于很宽温度范围内的低场各向异性磁阻...     

Features of magnetic properties of La x MnO3 + δ (0.815 ≤ x ≤ 1.0)

Magnetic and resonance studies of the system of polycrystalline samples of self-doped manganites La _x MnO_{3 + δ} (x = 0.815, 0.90, 0.94, 0.97, and 1.0) have been performed in a temperature range of 77–300 K. According to ⁵⁵Mn NMR data, all samples contain a ferromagnetic phase at 77 K. As the defect density increases (x changes from 1.0 to 0.815), samples become more magnetically ordered. In this case, the ferromagnetic state of the system gradually changes from a mixed state in which both ferromagnetic insulating (basic) and ferromagnetic metal (for x = 0.97 and 1.0) phases coexist to only the ferromagnetic metal state (for x = 0.815 and 0.90). It has been shown that both ferromagnetic metal and ferromagnetic insulating phases are inhomogeneous, and either phase consists of two phases with different dynamics of nuclear spins and different Curie temperatures. The diagram of the magnetic phase state of the La _x MnO_{3 + δ} system (x = 0.815, 0.90, 0.94, 0.97, 1.0) has been constructed for a temperature range of 120–240 K and Mn⁴⁺ contents of 12–30%.     

Structural and electronic properties of InNxP1-x alloy in full range (0 ≤ x ≤1)

We have performed first-principles method to investigate structural and electronic properties of InN_xP_1?x ternary semiconductor alloy in full range (0 ≤ x ≤ 1) using density functional theory. We have used modified Becke–Johnson potential to obtain accurate band gap results. From the electronic band structure calculation we have found that InN_xP_1?x become metal between 47 and 80% of nitrogen concentration. Additional to our band gap calculations, we have also used the band anticrossing model. The band anticrossing model supplies a simple, analytical expression to calculate the physical properties, such as the electronic and optical properties, of III-N_xV_1?x alloys. The knowledge of the electron density of states is required to understand and clarify some properties of materials such as the band structures, bonding character and dielectric function. In order to have a deeper understanding of these properties of the studied materials, the total and partial density of states has been calculated. Finally, we have calculated the total bowing parameter b of studied alloys, together with three contributions b_VD, b_CE, and b_SR due to volume deformation, different atomic electron negativities and structural relaxation, respectively.     

La0.7Sr0.3-x□xCoO3(0≤x≤0.2)钴氧化物中锶空位诱导的自旋态转变效应

研究了锶空位对La0.7Sr0.3-x□xCoO3(0≤x≤0.2多晶钴氧化物结构、磁性和输运性质的影响.结果表明:随着锶空位浓度x的增大,A位阳离子无序度增大,导致铁磁双交换作用减弱及反铁磁超交换作用增强,两者相互竞争,出现团簇自旋玻璃态;空位浓度超过10%后,Co-O键长迅速减小,导致晶体场劈裂能加大,大部分三价钴离子以低自旋态出现,系统基态为类超顺磁态,同时样品发生金属-绝缘体相变.     

Electron-phonon coupling through the orthorhombic to rhombohedral phase transition in La2/3(Ca1−xSrx)1/3MnO3 manganites

We present a systematic study of the Raman modes of a ferromagnetic series of manganites, La_2/3(Ca_1?xSr_x)_1/3MnO₃ with 0?x?1, that presents two different regimes for the variation of the ferromagnetic order temperature, T_C, with Sr doping. This change occurs for x～0.5 when the temperature of the orthorhombic, Pbnm, to rhombohedral, R-3c, structural phase transition, T_t, coincides with T_C. We have analyzed the evolution of the frequencies and widths of the observed Raman modes as a function of Sr doping and temperature. At room temperature, features of the Pbnm structure are detected for compounds up to x=0.6, over the orthorhombic phase limit x=0.45 at 300 K. Octahedra bending modes behave as expected with doping while the tilt mode, which is related to Mn–O–Mn angles and therefore to electronic conduction mechanisms, presents different behaviors in both structures. The tilt frequency is much less sensitive to Mn–O–Mn angle in R-3c than in Pbnm structure indicating a reduction of electron-phonon coupling. Its width presents an anomalous behavior both as a function of doping and temperature with unexpectedly large width in the rhombohedral phase.     

On-line phase transition in La1− x Sr x MnO3 (0.28 ≤ x ≤ 0.36) perovskites through ultrasonic studies

La_{1? x} Sr _x MnO₃ perovskite manganite materials with different compositions (x?=?0.28, 0.31 and 0.36) have been prepared employing solid-state reaction technique. On-line evaluation of ultrasonic velocities and longitudinal attenuation of the above samples has been done over a wide range of temperatures using the transmission method. The observed anomalies in velocities, attenuation and elastic moduli reveal the occurrence of lattice softening and hardening near Curie temperature. The observed dramatic hardening in sound velocities and softening in attenuation are correlated with the phase transition, i.e. ferromagnetic to paramagnetic. The increase in magnitude of maximum velocity with change in Sr content at T _c indicates the existence of linear magnetostriction effect. The elastic moduli study elucidates the observations made from the above-mentioned studies. The variation in the ultrasonic velocities, longitudinal attenuation and its derived parameters help us to understand the competitions between ferromagnetism and paramagnetism.     

Switching Behavior Induced by Electric and Magnetic Fields in （La0.73Bi0.27）0.67Ca0.33MnO3

Both electric and magnetic field-induced switching behaviors between a high resistive state and a low resistive one are observed in （La0.73Bi0.27）0.67Ca0.33MnO3. The effects of magnetoresistance a.nd electric-resistance suggest that the applied electric field and magnetic field greatly tune the percolative paths in the phase-separated system. According to the experimental results, the switching behaviors may come from the coexistence of the charge ordering state, and localized and freedom ferromagnetic states, in which the external field destroys partially the localized ferromagnetic states and charge ordering leads to the ferromagnetic state growth, which causes a switch between a high resistive state and low resistive one. This makes the doped manganite a good system for both electric and magnetic field sensor materials.