Spin Dependent Hopping in Ti Doped La0.67 Ca0.33 MnO3

A systematic investigation of the magnetic and transport properties of Ti doped La0.67Ca0.33MnO3 was reported. The Ti substitution for Mn ions results in a reduction in ferromagnetism and conductivity. The metal-insulator transition temperature is close to Curie temperature which decreases from 274 to 82 K as x increases from 0 to 0.17. The most important effect of Ti doping is to introduce spin clusters in the samples due to the distortion of local lattice and the inhomogeneous magnetic structure induced primarily by the random distribution of Mn ions. A maximum magnetoresistance ratio as large as 90% in 1 T at 122 K was obtained for the sample with x =0. 055, which is four times larger than that obtained for LCMO sample at 272 K. There is a remarkable field-history dependent MR in the cooling process for the doped samples while such phenomenon disappears in the warming run. The resistivity follows well the variable range hopping behavior in paramagnetic state. Both the size effect and spin dependent hopping of carriers between the spin clusters should be considered in this system.     

Spin-Dependent Electroresistance Behaviour of Nd0.67Sr0.33MnO3-δ(0≤δ≤0.20)

Oxygen deficient Nd0.67Sr0.33MnO3-δ ceramic samples were prepared using conventional ceramic technology. A colossal electroresistance (CER) effect was found in Nd0.67Sr0.33MnO3-δ series. The electrical transport is magnetically coupled and spin-dependent over grain or phase boundaries. Electrical-field-induced changes of the spin array orientations inside of and between the magnetic domains by grain or phase boundaries have to be concluded for the strong electroresistive effect in Nd0.67Sr0.33MnO3-δ series.     

Superconducting Transition Temperature in YBa2Cu4O8/La2/3 Ca1/3 MnO3 / YBa2 Cu4O8 Heterostructure

YBa2Cu4O8/La2/3 Ca1/3 MnO3/YBa2Cu4O8 （ Y-124/LCMO/Y- 124） heterostructure was prepared by facing-target sputtering technique. The oscillatory superconducting transition temperature was observed when the thickness of LCMO d L is larger than critical thickness d L^CR. The metal-insulator transition temperature can only be detected at d L 〉 d L^CR. The dependence on the spacer layer in LCMO/Y-124 systems suggests strongly the interplay of ferromagnetic and superconducting couplings.     

La0.67Sr0.33MnO3/La0.75MnO3/La0.67Sr0.33MnO3庞磁电阻三层膜的制备及结构形貌和性能

用磁控溅射法在(001)取向的LaAlO3单晶基片上制备了La0.67Sr0.33MnO3/La0.75MnO3/La0.67Sr0.33MnO3外延三层膜.结果表明, 与La0.67Sr0.33MnO3单层膜相比较, 外延三层膜的X射线衍射图上出现3级衍射峰, 每级衍射峰由3个峰组成其中强度最高的衍射峰代表衬底的衍射;次强的代表上下两层La0.67Sr0.33MnO3膜;最弱的代表中间La0.75MnO3层.三层膜的二维原子力表面形貌为均匀的小颗粒状, 表明其三维形貌为外延岛状柱状晶.这种三层膜的巨磁电阻效应与中间层La0.75MnO3的厚度有关, 当中间层厚度为70 nm时, 其最大磁电阻值可达到32%, 这个结果优于La0.67Sr0.33MnO3 单层膜的巨磁电阻效应.其可能的原因是电子在界面上的散射、层间的交互作用, 以及点阵错配导致的内应力的综合结果.     

Anisotropic Magnetoresistance of Perovskite La2／3Ca1／3 MnO3 ／YBa2Cu4O8／La2／3Cal／3MnO3 Trilayer Films

The anisotropic magnetoresistance (MR) of La2/3Ca1/3MnO3(LCMO)/YBa2Cu4O8 (YBCO) /LCMO sandwiches on (001) SrTiO3 were investigated. Single layer LCMO and sandwiches show in-plane anisotropy of MR. MR strongly depends on the magnetic field direction. A nearly sinusoidal dependence on the angle between the applied magnetic field and the film plane or transport current was observed. A positive MR was present with lower fields applied not only out-of-plane but also in-plane.     

Extraordinary Transport Behaviors of La0.67Sr0.33Mn1-x CrxO3（0.00≤x≤0.30）

The M-T curves, ρ-T curves and MR-Tcurves of La0.67Sr0.33 Mn1-xCrxO3 (0.00≤x≤0.30)were studied. The experimental results indicate that the substitution with Cr on Mn sites is impotent indriving Tc, but with the increase of Cr content, which leads to the appearance of two peaks in resistivity andCMR response, the temperature range of CMR response is significantly broadened. The extraordinary transport behavior and the abnormal CMR effect could be the results of the coexistence and competition of these Mn^3 -O-Mn^4 and Mn^3 -O-Cr^3 channels.     

Electrical Transport and Giant Magnetoresistance in （ 1 - x ） La0.67 Ca0.33 MnO3/x CuO Composites

Samples with nominal composition of （1 - x）La0.67Ca0.33MnO3 （LCMO）/xCuO （x = 0%, 2%, 4% and 20% ） were made using a special experimental method. The temperature dependence of the resistivity （ρ） of the composites was investigated in the temperature range of 10 - 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5, 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature （Tp）, zero field peak resistivity （ρmax）, and magnetoresistance （MR） properties of the composites. Tp shifted sharply towards low temperature with the increase of x in the range of x ≤4%, but was almost independent of x at high level of CuO content. Composites with x = 4 % and 20 % exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x =4% and 20% samples, the MR value at 0.3 T could reach as high as - 88% and - 90%, respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near Tp, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.     

Magnetic and Electrical Features of La0.67-xErxSr0.33MnO3 System and Anomalous Low-Temperature Resistivity Behavior

The system La0.67-x ErxSr0.33 MnO3 ( x =0.00, 0.10, 0.20) was investigated through the measurements of M-T, ρ-T and MR-T curves. The experiment results show that: with the increase of doping mount, the magnetic structure of the system transforms from long-range ferromagnetic order to cluster-spin glass state, and M-T curves turn upwards at extremely low temperature. The resistivity of the system inereases with the increase of doping amount, and exhibits the minimum value at low temperature. The change of magnetic and electric properties in the system comes from extra magnetic coupling induced by the doping,     

Extraordinary Transport Behaviors of La0.67Sr0.33Mn1-xCrxO3（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 Mn^3 ＋ -O-Mn^4 ＋ and Mn^3＋ -O-Cr^3 ＋ channels.     

Structure and Transport Properties in CMR Materials of La（1-x）2/3Ca1/3MnO3 with Rare Earth Vacancies

Samples of manganese oxides La（1-x）2/3Ca1/3MnO3（x 〈 0.10） with Lavacancy were prepared by standard solid-state reaction method. All the samples are single phase, with orthorhombic symmetry （Pnma ）, analyzed by XRD and with Rietveld Refinement. The effect of different La-site vacancies concentration on electronic transport of La（1-x）2/3Ca1/3MnO3 was investigated. The insulator-metal transition temperature （about 267 K） nearly remains unchanged with the increase of vacancy concentration, which indicates that small La-vacancy does not destroy the double exchange interaction. But the electronic resistance increases and MR value decreases with La-vacancy content x 〉 0.04. The maximum of the MR value （8 T） is about 220% at transition temperature （TMI）.     

Thickness Effect on Electronic Transport in Single Crystal La0.67 Ca0.33 MnO3 Thin Films

Lattice strain in thin films induced by film-sub-strate mismatchis one source for variant magnetic andresistive behaviors especiallyfor the manganite perovs-kites for which the lattice effects are wellestablished[1~5].It has been also reported that low-fi…     

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…     

Effect of heat treatment on electroresistance in Nd0.67Sr0.33MnO3 ceramics

A remarkable CER(colossal electroresistance) effect was observed in a series of polycrystalline Nd0.67Sr0.33MnO3 samples synthe-sized by high energy ball milling successive heat treatment.The CER ratio increased with increasing heating time and reached 3580% at a low temperature for the Nd0.67Sr0.33MnO3 ceramic annealed up to 13 h as measuring current was enhanced from 5 to 500 μA.The result showed that the CER effect was strongly dependent on the sample's microstructure,especially on the foreign phases whi...     

Structure and Transport Properties of La0.67Ca0.33Mn1-xAlxO3

The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La0.67Ca0.33MnO3. It is found that the volume of the crystal cell decreases monotonically when the population of Al3 increases across the entire doping range. As the Al3 population increases, the resistance of the material rises rapidly, while the insulator-metal transition temperature TIM decreases linearly. At small Al3 dosage, a thermal activation model properly describes the transport properties at T>TIM, while a metallic model is more suitable at T相似文献   

Epitaxial Growth of Gd0.67 Ca0. 33 MnO3 Thin Films by Laser Ablation

Gd0. 67Ca0. 33MNO3 (GCMO)thin films grown by laser ablation on SrTiO3 (100) (STO)substrates was studied. Films are highly crystallized, very well epitaxial and single-phased. The ordering magnetic temperature (Te)of the films is much higher than the value of bulk samples of similar composition. It is found that the GCMO film exhibits a reversal of its magnetization at low temperature when cooled under a magnetic field. The negative magnetization is a consequence of the rapid increase(～1/T) with decreasing temperature of the magnetization of a sublattice aligned antiparallel to the local field, relative to the magnetic izontribution of a second sublattice which is aligned parallel to the applied field.     

Calcination temperature effect on La0.67Ca0.33MnO3 nanoparticle using simple citrate pyrolysis process

A new simple route was used to synthesize nanosized crystalline La_0.67Ca_0.33MnO₃ perovskite type complex oxide by simple citrate pyrolysis process using a metal salts, La, Ca, Mn as starting materials. To obtain the LCMO nanoparticles the precursor was carried out at various calcination temperatures viz. 500° C, 600° C, 700° C, 800° C for very short time only ～ 60 minutes. The synthesized LCMO nanoparticles were characterized by powder XRD, FTIR, TGA/DTA, SEM. The precursor could be completely decomposed into complex oxide at temperature below 500° C according to the TGA/DTA results. XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600° C for 60 minutes. The crystalline size that depends on the calcination temperature of the precursor is in the range of 11–22 nm as determined by Scherrer Formula. All the prepared samples have high purity perovskite structure which is orthorhombic. The chemical bonds were identified by the measurements of Infrared IR transmission spectra carried out with powder samples in which KBr was used as a carrier. The IR spectra revealed that stretching and bending modes influenced by calcination temperature. Morphology and grain size were studied through scanning electron microscopy.     

Anisotropic Magnetoresistance of Perovskite La_(2/3)Ca_(1/3)MnO_3/YBa_2Cu_4O_8/La_(2/3)Ca_(1/3)MnO_3 Trilayer Films

Magneticanisotropyhasbeenfoundinmanyex oticmaterials,suchasmetallicsuperlatticeswithgi antmagnetoresistanceeffectsandthehightempera turesuperconductingoxideYBa2Cu3O7 δ[1～4].The anisotropycouldfindnovelusesinnewdeviceappli cations.Agoodexampleisthehig…     

Transport Properties of Rare Earth Manganese Oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3

CompoundsofthetypeLn1-xAxMnO3(Ln =rareearth ,A =Ca ,Ba ,Sr ,etc .)havebeenthepopularsubjectsofextensiveresearchrecently ,mainlyduetotheexistenceofcolossalmagnetoresistance(CMR ) [1～ 3] .Atroomtemperature ,theperovskitecompoundLnMnO3isantiferromagneticinsulatorwhereMnistrivalent .ThepartialsubstitutionoftrivalentLnionswithdivalentionssuchasCa ,Ba ,Sr ,andPbetc .yieldsanewcompoundexhibitingstrongferro magnetismandhighmetallicconductivity .Thetrans portpropertyinthesecompoundscanbepartly…     

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.