不同Ce掺杂比的La_(1-x)Ce_xMnO_3薄膜输运性质及机理研究（英文）

研究了电子型掺杂钙钛矿薄膜La_(1-x)Ce_xMnO_3的输运性质和外场作用下的输运机理。研究表明,La_(1-x)Ce_xMnO_3薄膜呈现出典型的金属-绝缘体转变,且与Ce的掺杂浓度相关。电阻-温度曲线表明,在低温时,电子-电子散射和磁畴对电子的散射是电阻形成的主要原因,而在高温下,小极化子的跳跃机制起主要作用。通过激光照射样品表面,发现光场诱导金属-绝缘体转变温度向着低温区偏移,该现象产生的原因在于La_(1-x)Ce_xMnO_3薄膜内部铁磁相与顺磁相的共存,此外,高能量的激光对样品的电阻变化影响更明显。进一步研究表明,Ce的掺杂浓度将会通过金属-绝缘相变对La_(1-x)Ce_xMnO_3薄膜的磁电阻效应产生显著的调制作用。     

高分子辅助沉积法制备Sm x Nd1- x NiO3 外延薄膜

采用高分子辅助沉积法制备掺杂不同钐（Sm）含量的Sm_xNd_1-xNiO₃外延薄膜（钐掺杂量x=0.5,0.55,0.6）。X射线衍射（特征θ-2θ扫描、摇摆曲线和φ-scan）和扫描电子显微镜的测试结果表明,制备的薄膜结晶性和外延性良好,与衬底的（001）取向保持一致。电阻率-温度曲线表明制备的外延薄膜均表现出金属绝缘体转变现象。随着Sm掺杂量的提高,金属绝缘体转变温度逐渐升高;当x=0.55时,外延薄膜的转变温度在室温附近。并且高分子辅助沉积法可以简单有效地制备热致变色外延薄膜。     

复合粘结La0.8Ce0.2Fe11.7- x Mn x Si1.3H1.8 磁工质的磁性能

采用中频感应炉制备La_0.8Ce_0.2Fe_11.7-xMn_xSi_1.3母合金并退火,将合金饱和氢化后破碎成粉末。通过环氧树脂粘结,将居里温度T_C间隔为5 K的多种La_0.8Ce_0.2Fe_11.7-xMn_xSi_1.3H_1.8（x=0.23,0.26,0.29,0.32,质量分数,%）合金粉末进行混合粘结,提高合金的磁熵半峰宽。用VersaLab和绝热温变直接测量仪测试粘结样品的磁性能。结果表明,与单一成分粘结样品相比,混合粘结样品的最大等温磁熵变有所降低,磁熵半峰宽以及相对制冷能力有所提高。含4种成分的混合粘结样品的相对制冷能力可以达到139.2 J/kg。     

Cu添加对La0.7Ce0.3Fe11.54-xCuxMn0.16Si1.3合金及其氢化物磁性能的影响

La(Fe, Si)₁₃系合金是具有一级相变大磁热效应的磁制冷合金,被认为是极具应用前景的磁热效应材料之一。本文采用高频感应悬浮炉制备了添加不同Cu元素比例的La_0.7Ce_0.3Fe_11.54-xCu_xMn_0.16Si_1.3(x=0, 0.05, 0.1, 0.15)合金。并利用粉末XRD衍射仪,扫描电镜(SEM)对合金的相组成、微观组织结构进行了研究,采用多功能振动样品磁强计VersaLab对合金的磁性能进行了分析。添加Cu元素后,合金的居里温度提高,但氢化后添加Cu的合金居里温度反而偏低。随着Cu元素提高磁热性能下降,但La_0.7Ce_0.3Fe_11.44Cu_0.1Mn_0.16Si_1.3H_1.68合金的最大等温磁熵变仍高达8.5 J/kg.K(0 ~ 2 T),相对制冷能力RCP提高(118 J/kg),磁滞明显降低。     

溶胶-凝胶法制备La1-xSrxMnO3及其电磁性能研究

采用溶胶凝胶法,制备了La_1-xSr_xMnO₃(LSMO)纳米微粉。探究了Sr^₂₊的掺杂量对LSMO晶体结构、磁学性质、电磁特性和微波吸收性能的影响。结果表明,随Sr^₂₊含量的升高,样品的晶格常数和Mn-O-Mn键角增大,平均晶粒尺寸逐渐下降,样品出现从反铁磁性向铁磁性的转变,复介电常数呈先增大后减小的趋势。在2~18GHz内,x=0的样品在厚度为2mm时有最佳吸波效果,反射率小于-10dB对应的有效吸波频段为12.5~18GHz;Sr^₂₊的掺杂可使吸波频段有效的向低频移动,在X波段内,x=0.2的样品在厚度为2.3mm时的有效带宽达2.6GHz,证明LSMO是一种性能优异的介电损耗型吸波材料。     

NEGATIVE THERMAL EXPANSION PHENOMENA\par OF Mn3(Cu1-xGexN

在氮气保护下于1073 K用固相烧结法制备了Mn₃(Cu_1-xGe_x)N化合物. XRD分析表明, 这类化合物具有Mn₃CuN型反钙钛矿相结构. 采用激光干涉法测量了Mn₃(Cu_1-xGe_x)N化合物的线膨胀系数. 结果表明, 当Ge含量为0.40≦x≦0.60时, Mn₃(Cu_1-xGe_x)N在一定温度范围内出现负热膨胀现象; 随Ge含量的增加, 发生负热膨胀的温度升高且温区变宽, 而负热膨胀性能减弱. 当x=0.60时,发生负热膨胀的温度范围为250-290 K(273 K附近), 线膨胀系数为-65×10^-6 K^-1, 具备应用潜力. 热磁曲线表明, Mn₃(Cu_1-xGe_x)N化合物的负热膨胀现象发生在反铁磁性逐渐向顺磁性转变的过程中,由磁有序逐渐消失、自发磁化强度减小所引起的磁容积效应造成的.     

微量B元素添加对Fe81Ga19合金磁致伸缩性能的影响

本文采用真空熔炼法制备(Fe₈₁Ga₁₉)_1-xB_x(x=0,0.06,0.1,0.15,0.20)系列铸态合金,通过X射线衍射、扫描电镜及配套的能量色散谱、金相显微镜表征合金的微观结构、形貌及成分,利用电阻应变片法测量合金的磁致伸缩性能。结果表明,微量的B元素添加提高了合金的磁致伸缩性能, 在x=0.10时最大达到最大饱和磁致伸缩值λs=138ppm。研究表明,(Fe₈₁Ga₁₉)_1-xB_x合金结构为α-Fe体心立方为主。B元素的添加,一部分进入晶格间隙,引起晶格畸变,提高合金磁致伸缩性能,另一部分以富B析出相的形式分布在晶粒内部;合金添加B元素后,晶粒变为对磁致伸缩性能有利的大柱状晶,大柱状晶由于晶界少,减少阻碍磁畴运动的因素,有利于合金的磁致伸缩性能。     

Mn1-xZnxFe2O4 (0≤x≤1)纳米粉体的模板辅助溶胶凝胶法制备及其磁性能研究

通过模板辅助溶胶-凝胶法制备了一系列的Mn_1-xZn_xFe₂O₄(0≤x≤1,步长为0.2)纳米粉体。利用XRD和VSM对材料的物相和磁性能进行了表征,主要研究了Mn_1-xZn_xFe₂O₄分子式中Zn含量的变化对样品的微观结构和磁性能的影响。实验结果表明,具有不同Zn含量的Mn_1-xZn_xFe₂O₄样品均为尖晶石结构;随着Zn含量的增加,样品的晶面间距d、平均晶粒尺寸D、饱和磁化强度M_s和居里温度T_c都呈现出下降的趋势,而样品的矫顽力H_c则呈现出先升高后降低的趋势。分析认为,M_s的下降可以用Yafet-Kittel倾角理论解释,T_c的降低归因于晶格中反铁磁性耦合的降低,而H_c的变化则主要是由于材料的磁晶各向异性常数K₁的变化引起的。     

298 K下离子液体BMIMPF6 中电沉积制备镧金属薄膜

以无水硝酸镧、1-丁基-3-甲基咪唑六氟磷酸（BMIMPF₆）和助溶剂丙酮为电解液,在室温（298 K）下电沉积制得镧金属薄膜。电解液BMIMPF₆的电化学窗口为-2.5~1.5 V vs. Pt,La³⁺还原为La²⁺发生于-1.7 V vs. Pt,La²⁺还原为La⁰发生于-2.1 V vs. Pt。BMIMPF₆的低吸湿性有利于在空气气氛下电沉积镧。使用扫描电子显微镜和光学显微镜观察到所制备的薄膜织构致密,经能量色散谱和X射线光电子能谱对沉积薄膜进行了表征,确定了薄膜中含有大量镧元素。通过探究电压扫描速率和硝酸镧浓度对La³⁺的电化学行为的影响,证明La³⁺的还原反应是一个受物质扩散控制的不可逆过程,La³⁺在BMIMPF₆中的扩散系数为1.47×10^-9 cm²·s^-1。本研究为获得金属镧薄膜和镧氧化物薄膜提供了一种简便的方法,并且有望用于电沉积制备其它镧系元素薄膜。     

MAGNETIC PROPERTIES OF Co1-xNixFe2O4/SiO2 NANOCOMPOSITES

采用溶胶--凝胶法制备了Co_1-xNi_xFe₂O₄/SiO₂(0 ≤x ≤1.0)纳米复合材料. 利用XRD, TEM, 振动样品磁强计(VSM)和Mossbauer谱测试了900℃热处理样
品的结构、晶粒尺寸和磁性. 结果表明, 样品中Co_1-xNi_xFe₂O₄铁氧体的平均晶粒尺寸在15---20 nm之间, Ni²⁺的掺杂引起CoFe₂O₄晶胞体积减小. VSM结果表明, 随Ni²⁺含量的增加, 样品的比饱和磁化强度和矫顽力变小. Mossbauer谱表明, 室温下各样品均处于磁有序状态, 样品的内磁场随Ni²⁺含量的增加而变小.     

1:13 phase formation mechanism and first-order magnetic transition strengthening characteristics in (La,Ce)Fe<Subscript>13–<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The effects of the introduction of Ce to La_1?x Ce _x Fe_11.5Si_1.5 alloys on 1:13 phase formation mechanism, the first-order magnetic phase transition strengthening characteristics, and magnetocaloric property were studied, respectively. The results show that the formation mechanisms of 1:13 and LaFeSi phases in La_1?x Ce _x Fe_11.5Si_1.5 alloys are the same as those of Ce₂Fe₁₇ and CeFe₂ phases in Ce–Fe binary system, respectively. The substitution of Ce in 1:13 phase which is limited can make the first-order magnetic phase transition characteristics strengthen, which can make thermal and magnetic hysteresis increase, the temperature interval of temperature-induced phase transition decrease, and the critical magnetic field of field-induced magnetic phase transition (H _C) increase, respectively. Owing to the lattice shrink of 1:13 phase with the increase in Ce content, the Curie temperatures (T _C) show a linear decrease. The maximum change in magnetic entropy gradually increases due to the decrease in temperature interval of temperature-induced phase transition, but the relative cooling capacities are all about 80 J·kg^?1 at magnetic field of 2 T.     

Large magnetic entropy change near room temperature in La0.7(Ca0.27Ag0.03)MnO3 perovskite

In this paper, the magnetic properties and magnetocaloric effect (MCE) of La_0.7(Ca_1−xAg_x)_0.3MnO₃ (x = 0, 0.1, 0.2, 0.7, and 1) powder samples are reported. Our polycrystalline compounds were synthesized using the solid state reaction method at high temperature. Magnetization measurements versus temperature showed that all our samples exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature, T_C, has been found to increase from ∼250 K for x = 0-270 K for x = 1. Ag doping weakens the first order phase transition, and at higher Ag doping, the phase transition is of second order. For the La_0.7(Ca_0.27Ag_0.03)MnO₃ composition, the maxima of the magnetic entropy changes from the applied magnetic field (ΔS_M) at 2 and 5 T are about 4.5 and 7.75 J/kg K, respectively, at the Curie temperature of ∼263 K. The relative cooling power (RCP) values without hysteresis loss are about 102 and 271 J/kg for the applied fields of 2 and 5 T, respectively. Due to the large ΔS_M, large RCP, and high Curie temperature, La_0.7(Ca_0.27Ag_0.03)MnO₃ is promising for application in potential magnetic refrigeration near room temperature.     

Post annealing effect on transport properties of La0.67Ca0.33MnO3 films grown on vicinal cut substrates

La_0.67Ca_0.33MnO₃ thin films have been grown on 10°, 15°, and 20° vicinal cut SrTiO₃ (1 0 0) substrates by pulse laser deposition. The single phase and the least textured growth have been studied by X-ray diffraction analysis. The post annealing effect with high temperature and high oxygen pressure on the transport properties of films has been investigated by resistance versus temperature measurements. Films with post annealing show large enhancement of metal-insulator transition temperature T_p about 20-30 K towards higher temperature and obvious decrease of resistance, which is attributed to the refilling of oxygen, the change of Mn-O-Mn angle and the improvement of crystallinity by the post annealing effect. Specially, film on 20° vicinal cut substrate exhibits the biggest range gap of peak resistance drop, which may originate from more defects caused by steps at this tilt angle and many of these defects are removed after post annealing.     

Multiphase magnetic state of Ca1 ? x La x MnO3 ? δ single crystals ( x = 0.03, 0.05, 0.07) containing oxygen vacancies

Magnetic properties (magnetization, dynamic and static susceptibility) and transport properties (resistance and magnetoresistance) have been studied in a temperature range of 2–600 K in magnetic fields to 90 kOe for single crystals of Ca_{1 − x} La _x MnO_{3 − δ} with a weak electron doping (x ≤ 0.07) grown in argon and oxygen atmospheres. The magnetic state of Ca_{1 − x} La _x MnO_{3 − δ} single crystals is multiphase. Below T = T _N(G) ∼ 110 K, in all the crystals there coexists an AFM G phase with an FM contribution and an AFM C phase. In crystals with x = 0.07, a transition from the paramagnetic phase into the AFM C phase occurs in part of their volume below T ∼ 130–150 K. In crystals with x = 0.05 annealed in oxygen, an anomaly of paramagnetic susceptibility is observed near T ^* ∼ 270 K, which is related to the formation of FM clusters near defects. At x = 0.05 and 0.07, AFM correlations are retained in the paramagnetic state (to 600 K). The differences in the magnetic and transport properties of single crystals grown in argon and oxygen are explained by the various content of oxygen vacancies and by their possible ordering. Original Russian Text ? N.N. Loshkareva, A.V. Korolev, T.I. Arbuzova, N.I. Solin, A.M. Balbashov, N.V. Kostromitina, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 103, No. 3, pp. 261–270.     

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

The effect of LMO doping on the structure, magnetic and magnetotransport properties of La_0.8Sr_0.2MnO₃ (LSMO)/xLaMnO₃ (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SL_x (low temperature sintered samples) and SH_x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL_x samples and 0 ≤ x ≤ 10 for SH_x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.     

Studies on La0.67Ca0.33MnO3-SrTiO3 composites using two-phase model

In this study we report the structural, electrical and magnetic properties of (1 − x)La_0.67Ca_0.33MnO₃ (LCMO)-(x)SrTiO₃(STO) composites. For this series we have observed a minute change in ferromagnetic (FM)-paramagnetic (PM) transition temperature with STO addition in LCMO matrix; however a reasonable change is observed in metal-insulator transition temperature, along with the occurrence of percolation threshold for x = 0.30 sample. Overall pattern for temperature dependence of resistivity for this series has been best-fitted using the formula 1/ρ = (1 − f)/ρ_PM + (f/ρ_FM), whereρ_PM and ρ_FM are the resistivities of the PM and FM contents in the sample and f is the volume fraction of FM phase in the sample. Investigations on magnetoresistance (MR) using magnetic field up to 3 T show enhancement of extrinsic MR in the composite samples which can be viewed in the light of spin polarized tunneling.     

Effect of Eu doping on structural and magneto-electrical properties of La0.7Ca0.3MnO3 manganites

We have investigated the influence of europium (Eu) doping on structural and magneto-electrical properties of La_0.7Ca_0.3MnO₃ compounds. In order to analyze the physical mechanism of a spin disorder system and study their relative evolutions, two samples of nominal compositions (La_0.7?xEu_x)Ca_0.3MnO₃ (x = 0.0 and 0.1) have been elaborated and characterized. In addition to structural changes seen by this kind of doping, the magnetoresistance (MR) and resistivity are increased while the metal–insulator transition temperature is decreased. Comparing the experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behaviour of both samples is quite well described by a theory based on Kondo-like spin dependent scattering, electron–electron scattering, electron–phonon and electron–magnon scatterings. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping model is found to fit well the experimental curves.     

Structures, electrical and thermal expansion properties of Sr-doped La2Mo2O9 oxide-ion conductors

The oxide-ion conductors (La_1−xSr_x)₂Mo₂O_9−δ (x = 0.01–0.08) were prepared by means of a conventional solid-state reaction. The effects of Sr doping for La site on the structures, electrical and thermal expansion properties of the oxide-ion conductor La₂Mo₂O₉ were investigated using X-ray diffraction, direct current four-probe method, thermal dilatometer and scanning electron microscopy, respectively. The results show that the lattice constants were first decreased, then increased, and decreased again with the increase of Sr doping content. The solid solubility of Sr in (La_1−xSr_x)₂Mo₂O_9−δ is x = 0.07. The sinterability of samples is markedly improved with the increase of Sr doping content. The sintered density of sample x > 0.07 is higher than 96% of its theoretical density. When x > 0.02, doping Sr in La₂Mo₂O₉ can inhibit the excessive growth of grains, thus increases the sintered density of samples. The structural transition temperature shifts to the low side with the increase of Sr doping content, and the phase transition is completely suppressed when the doping content reaches 0.07. The conductivity of sample increases with the increase of Sr doping content. The conductivity of sample x = 0.07 reaches a maximum of 0.078 S/cm and 0.101 S/cm at 800 °C and 850 °C, respectively. In this study, it was demonstrated that doping 7 mol% Sr for La site not only can completely suppress the structural phase transition in La₂Mo₂O₉, but also can effectively enhance electrical conductivity of samples at higher temperature.     

Optical properties of buffer and superconducting layers of the YBa2Cu3O7 ?δ/La1.75Ba0.25CuO4/La0.8Ba0.2MnO3 heterostructure for second-generation superconducting cables on an Ni5% W tape

An epitaxial YBa₂Cu₃O_{7 − δ}/La_1.75Ba_0.25CuO₄/La_0.8Ba_0.2MnO₃ heterostructure has been obtained on a biaxially textured tape of an Ni5% W alloy. It is shown that when films of a buffer layer of La_0.8Ba_0.2MnO₃ applied onto a tape of an Ni alloy in a reducing atmosphere are annealed in an oxygen atmosphere it is the compensation of oxygen vacancies that plays the dominant role in the formation of optical and magnetooptical properties of the layer, rather than stresses at the film-substrate interface. The shape of the reflection spectrum of the buffer layer after annealing corresponds to that of an La_0.8Ba_0.2MnO₃ single crystal, which indicates that the oxygen content is close to the stoichiometric one. The temperature dependences of the transverse Kerr effect and coefficient of light reflection of the films at a fixed wavelength can be used for the evaluation of T _c and the temperature of the optical response of the metal-insulator transition of the buffer layer on the basis of lanthanum manganite. Original Russian Text ? O.Yu. Gorbenko, A.R. Kaul’, Yu.P. Sukhorukov, E.A. Gan’shina, S.V. Samoylenkov, N.N. Loshkareva, A.V. Telegin, O.V. Melnikov, O. Stadel, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 104, No. 6, pp. 578–585.     

The effect of high-temperature annealing on LaFe_(11.5)Si_(1.5) and the magneto-caloric properties of La_(1-x)Ce_xFe_(11.5)Si_(1.5) compounds

The powder X-ray diffraction patterns of LaFe11.5Si1.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFe11.5Si1.5 compound annealed at 1423 K (5 h). In the temperature range from 1423 to 1523 K, α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed, and the most amount of 1:13 phase is obtained in the compound annealed at 1523 K (5 h). With the annealing temperature increasin...