Current-voltage characteristics with several threshold currents in insulating low-doped La1-xSrxMnO3 （x=0.10） thin films

The current-induced resistive switching behavior in the micron-scale pillars of low-doped La0.9Sr0.1MnO3 thin films using laser molecular-beam epitaxy was reported. It was demonstrated that the current-voltage curves at 120 K showed hysteresis with several threshold currents corresponding to the switching in resistance to metastable low resistance states, and finally, four closed loops were formed. A mode was proposed, which was based on the low-temperature canted antiferromagnetism ordering for a lightly doped insulating regime.     

La0.67-xDyxSr0.33MnO3(0.00≤x≤0.30)中的晶格效应

用固相反应法在La0．67-xDyxSr0．33MnO3中进行了Dy掺杂研究。结果发现，随着Dy掺入量的增加，样品的金属一绝缘体相变温度逐渐降低，对应的峰值电阻渐渐增大，居里温度下降，样品的磁电阻效应迅速增加，对Dy掺杂的作用可以用晶格效应来解释。     

Extraordinary Transport Behaviors of La0.67Sr0.33Mn1-x Crx O3 (0.00≤ x ≤0.30)

M-T curves, ρ-T curves and MR-T curves of La0.67Sr0.33Mn1-xCrxO3(0.00≤ x ≤0.30) were studied. Experimental results indicate that the substitution of Cr on Mn sites is impotent in driving TC, but with an increase of Cr content, there appear two peaks in resistivity and MR response, thus the temperature range of CMR response is significantly broadened. The extraordinary transport behavior and the abnormal CMR effect could be the results of coexistence and competition of Mn3 -O-Mn4 and Mn3 -O-Cr3 channels.     

Magnetic Properties of La1-xSrxCoO3 (0≤x≤0.5)

The measurements of temperature dependence of the magnetic susceptibility of La1-xSrxCoO3 perovskite oxides at different Sr doping (0≤x≤0.5) and annealing temperature were presented. For the sample with x=0.1, a shoulder was observed around 150 K, and a peak which is one feature of spin glass appeared around 50 K in the curve of susceptibility versus temperature. The high-temperature(250～420 K)susceptibility fits well with Curie-Weiss law for all samples. Weiss constant and effective magnetic moment were determined and their variations with Sr doping and oxygen annealing condition were obtained. The Weiss constant increases monotonously with Sr content for x>0.2. The values of effective moments were interpreted with the spin state of cobalt ions. Studies on the susceptibilities of the samples with x=0.2 under different preparation temperatures and annealing temperatures show that the rising of sintering temperature and annealing temperature will increase the para-ferromagnetic transition temperature, and reduce the effective moment to normal value. Our result shows that both Co3 and Co4 ions should be in IS state after annealing and the oxygen annealing causes the transition of Co3 spin state from HS to IS.     

Research of Colossal Magnetoresistance in La0.67Ca0.33Mn1-xCrxO3 (0.00≤x≤0.15)

The extraordinary colossal magnetoresistance (CMR) behavior in was found that the substitution with Cr on Mn sites introduces an additional bump in zero-field resistivity. With increasing Cr content, this additional bump grows up drastically while the original resistivity peak associated with magnetic order transition diminishes gradually. Under the applied magnetic field, both bumps of resistivity are deeply compressed, which leads to the appearance of two peaks in CMR response. As a result, the temperature range of CMR response is significantly broadened, spanned from the lowest to near room temperature. These results suggest that Mn-site element substitution could be a potent way of tuning CMR response.     

Electrical and Magnetic Properties of Bilayer Manganites La1.4Sr1.6Mn1.96TE0.04O7 （TE = Mn, Fe, Ti, Nb）

The electrical and magnetic properties of bilayer manganites La1.4Sr1.6Mn1.96TE0.04O7（TE = Mn, Fe, Ti, Nb） were investigated. Doping caused obvious changes in electrical and magnetic behaviors such as decrease of insulator-metal transition and magnetic transition temperatures, increase of peak resistivity, and different magnetoresistance effect. These changes had a significant degree of correlation with the valence of doped ions. From Fe, Ti to Nb doping, the effect was doubly stronger. The results could be well understood by considering the different destructions on double-exchange interaction and different influences on lattice distortion caused by Fe, Ti and Nb doping. The temperature dependence of magnetization measured at high field showed that the influence of doping was greatest near three-dimensional magnetic transition temperature of parent phase.     

Structural and Electrical Properties of Layered Pervoskite Manganites Nd2-2x Sr1＋2x Mn2O7 （x=0.25, 0.3, 0.4）

Tetragonally layered perovskite manganites of Nd2-2xSr1＋2xMn2O7（x =0.25, 0.3, 0.4） were fabricated by using solid-state reaction technique. Structural characterization of the compounds was investigated by X-ray diffraction （XRD） and FT-IR absorption spectra. The XRD patterns revealed that all the samples were single phase. X-ray photoemission spectroscopy （XPS） was used to investigate their electronic structures. It was found that manganese was in mixed states of Mn^3＋ and Mn^4＋ whereas lattice oxygen and chemical absorbed oxygen were existed in all the samples. The high temperature electrical properties of Nd2-2xSr1＋2xMn2O7 （x = 0.3, 0.4） were measured by standard four-probe technique. The results showed that both compounds had semi-conductivity behavior in the temperature range of 300 - 1073 K, and the electrical conduction was dominated by thermally activated behavior above 500 K.     

Microwave dielectric properties of Ba6-3xLa8+2x(Ti1-zZrz)18O54(x=2/3)ceramics

Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2xTi18O54(x=2/3) ceramics.A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0     

Magnetic and Magnetoresistance Properties in （La0.67Ca0.33MnO3）x／（ZrO2）1-x Composite System

Inrecentyears,muchattentionhasbeenpaidto therare earthdopedmanganitesduetotheirextraor dinarymagneticandtransportproperties.Onone hand,itisbecausetheirabundantelectronicstructure andmagneticproperties[1];ontheotherhand,they exhibitcolossalmagnetoresistan…     

Microstructure and magnetic properties of bulk magnets Nd_(14-x)Fe_(76+x)Co_3Zr_1B_6(x=0,0.5,1) prepared by spark plasma sintering

Melt-spun ribbons with nominal composition of Nd14-xFe76+xCo3Zr1B6(x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method.It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets.Homogeneous microstructure and fine grain(50-100 nm) were obtained when sintering below 700 ℃,and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism.However,ab...     

Luminescence properties of a new red emitting Eu~(3+)-doped alkaline-earth fluoborate phosphor: BaCa_(1-2x)BO_3F:xEu~(3+), xM~+ (M=Li, Na, K)

A series of new red-emitting BaCa1-2xBO3F:xEu3+, xM+ (M=Li, Na, K) phosphors were synthesized by the solid-reaction method. X-ray diffraction (XRD), diffuse reflection (UV-vis) and photoluminescence spectra were utilized to characterize the crystallization process, structure and luminescence properties of the as-synthesized phosphors. The XRD results indicated that the sample began to crystallize at 800 oC, and single-phase BaCaBO3F was fully obtained after annealing at 1000 oC. The charge compensated behav...     

Large Magnetic Entropy Effect in La2／3Ca1／3MnO3

The magnetocaloric effect in the colossal magnetoresistance material La2/3Ca1/3MnO3 was studied. From the measurements of temperature dependence of magnetization in various magnetic fields, the large magnetic entropy change associated with the ferromagnetic-paramagnetie transition was discovered. This result suggests that perovskite manganites are suitable candidates as working substance in magnetie refrigeration technology.     

Magnetocaloric Effect in Colossal Magnetoresistance Material（ La0.6 Dy0.1 ） Sr0.3 MnO3

The magnetocaloric effect was discovered in 1881by Warburg[1]. When a magnetic field is applied to amagnetic material, the unpaired spins are aligned par allel to the magnetic field, which lowers the magneticentropy and causes the sample to heat up. I…     

Magnetic Entropy Change of （Gd1-xREx）5Si4（RE = Dy, Ho） Alloys

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys     

Crystal structure, thermal expansion and electrical conductivity of Pr(Ga1-xCox)0.9Mg0.1O3-δ(x=0,0.1,0.2,0.3)

Pr(Ga1-xCox)0.9Mg0.1O3-δ(x=0, 0.1, 0.2, 0.3) was synthesized using solid-state reaction technique to study the effects of Co doping on their structure and properties. Room and high temperature XRD, DSC and electrical conductivity measurement with D.C. four-probe technique were adopted in the study. The results indicated its orthorhombic-distorted perovskite structure at room temperature. PrGa0.9Mg0.1O3-δ maintained its orthorhombic-distorted structure between 298 and 1173 K. For Pr(Ga0.7Co0.3)0.9Mg0.1O3-δ, such structure existed below 873 K. From 873 to 1173 K, it possessed tetragonal structure. The transformation from orthorhombic to tetragonal structure at 873 K was of second order. The intrinsic volume thermal expansion of tetragonal structured Pr(Ga0.7Co0.3) 0.9Mg0.1O3-δ was about 50% higher than those of PrGa0.9Mg0.1O3-δ. The electrical conductivity increased with Co content. The activation energies of conduction for Pr(Ga1-xCox)0.9Mg0.1O3-δ are in range from 0.197 to 0.246 eV, much lower than 1.543 eV for PrGaO3.     

Research of Luminescence Properties on MO-RE2 O3 -B2 O3:Eu, Mn(M=Mg, Ca, Sr; RE=Y, La, Gd)

A series of phosphor of MO-RE2 O3-B2 O3: Eu, Mn ( M = Mg, Ca, Sr; RE = Y, La, Gd) were prepared and studied.Excitation spectra exhibited high absorption in UV region (370 ～ 400 nm).There existed two valence states for europium ions Eu2 and Eu 3 , the broad emission band peaking at 515 nm correspond to the 5d-4f emission transition of Eu2 , the sharp emission peaking at 590 and 610 nm correspond to the 5D0→7FJ(J = 1,2,3,4) emission transition of Eu 3 By the introduction of Mg and Y into MO-RE2O3-B2O3: Eu, blue-green emission was restrained ultimately and red emission peaking at 610 nm was enhanced strongly, intensity and colorimetric purity of red light were both enhanced.Furthermore, Mg1-xSrxO-Y2O3-B2O3: Eu was also researched, the introduction of Sr into MgO-Y2O3-B2O3:Eu gives rise to a shift to longer wavelengths of the position of the excitation peak, and the emission spectra varies with the increasing of x simultaneously.     

Synthesis, Characterization and Thermal Decomposition of Ln (Me2dtc)3(phen) (Ln=La, Pr, Nd, Sm)

Four solid complexes of Ln(Me2dtc)3(phen) (Ln=La, Pr, Nd, Sm) were synthesized in anhydrous ethanol by the reaction of lanthanide chloride low hydrate with the mixed ligand of sodium dimethyldithiocarbamate and 1, 10-phenanthroline·H2O (phen·H2O), and characterized by elemental analysis, IR spectroscopy, TG-DTG, and X-ray diffraction analysis. TG-DTG with X-ray powder diffraction showed that these compounds could decompose to lanthanide sulfides at relatively lower temperature, which indicated that the title complexes could be favorable precursors to prepare lanthanide sulfides.