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.     

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.     

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…     

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.     

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.     

Effect of Ag substitution on structural,magnetic and magnetocaloric properties of Pr_(0.6)Sr_(0.4–x)Ag_xMnO_3 manganites

A systematic investigation on the structural, magnetic and magnetocaloric properties of Pr_(0.6)Sr_(0.4-x)Ag_xMnO_3(x=0.05 and 0.1) manganites was reported. Rietveld refinements of the X-ray diffraction patterns confirmed that all samples were single phase and crystallized in the orthorhombic structure with Pnma space group. Magnetic measurements in a magnetic applied field of 0.01T revealed that the ferromagnetic-paramagnetic transition temperature T_C decreased from about 293 to 290 K with increasing silver content from x=0.05 to 0.1. The reported magnetocaloric entropy change and relative cooling power for both samples were considerably remarkable with a △S_(max) value of 1.9 J/(kg·K)and maximum RCP values of 100 J/kg, under a magnetic field change(?μ0H) equal to 1.8T. The analysis of the universal curves gave an evidence of a second order magnetic transition for the studied samples. The magnetic field influence on both the magnetic entropy change and the relative cooling power was also studied and discussed.     

Transport Property of La0.67-xSmxSr0.33MnO3 at Heavy Samarium Doping （0.40≤x≤0.60）

The influence of heavy samarion （Sm） doping （0.40≤x≤0.60） on magnetic and electric properties of La0.67-xSmxSr0.33MnO3 was investigated by measuring the magnetization-temperature （M - T） curves, magnetization-magnetic density （ M - H） curves, resistivity-temperature （ρ- T） curves and magnetoresistivity-temperature （ MR - T） curves of the samples under different temperatures. It is found that, form from long-range ferromagnetic order to spin-cluster glass with the increase of Sm doping amount, the samples transstate and anti-ferromagnetic state; and when x = 0.60, the transport property becomes abnormal under magnetic background; and the magnetic structure changes and extra magnetic coupling induced by doping leads to colossal magnetoresistance effect. The transport mechanism of metallic conduction at low temperature is mainly electron-magneton interaction and can be fitted by the formula ρ = ρ0 ＋ AT^4.5, and the insulatorlike transport mechanism on high temperature range is mainly the function of variable-range hopping and can be fitted by the formula ρ = ρ0exp（T0/T）^1/4. In the formulas above, p is resistivity, T is temperature, and A, ρ0, T0 are constants.     

Effect of Yb2O3 additives on structure and transport properties of YBa2Cu3O7-δ

The effects of Yb2O3 particles on the microstructure and transport properties of YBa2Cu3O7-δ(YBCO) were investigated through resistance-temperature(R-T),scanning electron microscope(SEM),X-ray diffraction(XRD) and the critical current density(Jc) versus applied magnetic field(Jc-B) measurements.YBCO powder with Yb2O3 additives was synthesized using standard solid state reaction technique.Rietveld refinements of X-ray diffraction showed that both Yb2O3 and YBCO phases coexisted in the products.The critical current density(Jc) exhibited a maximum at x=0.05 in YBCO+xYb2O3 systems.Moreover,small additions of Yb2O3 in YBCO could enhance Jc by applying the magnetic field,although the superconducting temperature(Tc) decreased monotonically with increasing additive content.The characteristic behavior of Jc might come from the counterbalance of two effects simultaneously,which was caused by the inhomogeneity of grains distribution in nano-scale and degradation on superconducting properties.     

Magnetic Coupling in La0.67 Ca0.33 MnO3／La0.67 Sr0.33 CoO3／La0.67 Ca0.33MnO3 Trilayer Films

The perovskite La0.67 Ca0.33 MnO3/La0.67 Sr0.33 CoO3/La0.67 Ca0.33 MnO3 trilayers were fabricated by a facing-target sputtering technique and their magnetotransport properties were investigated. The magnetoresistance is dependent on spacer thickness and dramatically decreases when La0.67 Sr0.33 CoO3 layer is thick enough because of its short-circuiting effect. Different from La0.67 Ca0.33 MnO3 single layer, trilayer films with thin La0.67 Sr0.33 CoO3 spacer have the enhanced metal-semiconductor transition temperature (TMS) of La0.67 Ca0.33 MnO3 layers. The magnetic coercivity Hc shows a nonmonotonic behavior with changing the spacer layer thickness at 230 K. The waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom Lao.67 Ca0.33 MnO3 layers across the spacer La0.67 Sr0.33 CoO3 layer.     

Magnetocaloric and magneto-transport properties of Gd10Co20Si70 alloy

We report the results of magnetic, thermodynamic, transport and magnetocaloric effect (MCE) studies of newly synthesized Gd_(10)Co_(20)Si_(70) alloy. These measurements confirm an antiferromagnetic transition at T_N=9 K. Both MCE and magnetoresistance (MR) show quadratic dependence on the applied magnetic field, indicating the presence of spin fluctuations in the alloy. The maximum values of the magnetic entropy change determined from the isothermal magnetization data for magnetic field change of 7 and9 T are found to be 10.5 and 15.6 J/kg·K, respectively. As a consequence of the spin fluctuations effect, the MCE peaks are pulled towards high temperature side as asymmetrically broadened peak. The MR attains a large positive value of 73%at 2 K in 8 T. The large MR and reversible MCE make this alloy an attractive multifunctional magnetic material.     

Effects of High Magnetic Field on Microstructure and Properties of Low Aspect Ratio Bi₂Sr₂CaCu₂O_x/AgMg Wire

Here,we report the effect of an 8 T magnetic field on the microstructure and properties of a reetangular Bi₂Sr2CaCu20x/AgMg（Bi2212/AgMg）conductor with low aspect ratio.The magnetic field was applied during split melt process with the field direction perpendicular and parallel to the wide surface of the conductors.After heat treatment,the conductors were electrically characterized using four-point critical current measurements as a function of magnetic field and magnetic field orientation relative to the conductor.The superconducting transition and magnetization hysteresis were measured using a SQUID magnetometer.The microstructure was characterized using scanning electron microscopy.It was found that the presence of magnetic field during split melt processing enhances the electrical transport and magnetic behavior.The magnetic field increases the Bi2212 grains alignment and long range texture within filaments and bridges between filaments by textured growth of Bi2212 phase.     

Bifunctional luminescent and magnetic core/shell type nanostructures Fe3O4@CeF3：Tb^3＋/SiO2

A facile co-precipitation and microemulsion methods were applied to obtain core/shell type nanoparticles.Cerium fluoride doped with terbium(III) ions supplied intensive green luminescence of the system.Due to the presence of magnetite nanoparticles as cores,the prod-uct was highly sensitive to external magnetic field.Both sorts of nanostructures were encapsulated by silica shell.Such external layer of inert oxide can potentially increase the resistance of prepared nanostructures to thermal oxidation,aggressive agents,changing of pH or destructive radiation.Morphology of the product was examined using transmission electron microscopy(TEM) .Formations of the core/shell type nanos-tructures were clearly seen in the TEM pictures.Powder X-ray diffraction(XRD) confirmed the structure of the products,their nanocrystallin-ity and amorphous nature of silica shell.Optical properties were investigated by measuring excitation and emission spectra.Such multifunctional luminescent and magnetic nanoparticles coated with easily functionalized silica shell could be applied in many field of science.     

Influence of the substitution of Sm, Gd, and Dy for La in La_(0.7)Sr_(0.3)MnO_3 on its magnetic and electric properties and strengthening effect on room-temperature CMR

A series of La0.7–xSmxSr0.3MnO3, La0.7–xGdxSr0.3MnO3, and La0.7–xDyxSr0.3MnO3 (x=0.00, 0.10, 0.20, 0.30) samples were prepared by the solid-state reaction method. The influence of the substitution of Sm, Gd, and Dy for La on the magnetic and electric properties and on the magnetoresistance (MR) was studied through measurements of M-T curves and ρ-T curves. The results showed that: lattice distortion in-duced by substitution of Sm, Gd, and Dy for La and extra magnetism of substitution had great influence on the magnetic and electric proper-ties of perovskite manganites; substitution of magnetic rare earth element for La was an effective way to change Curie temperature and to strengthen MR in perovskite manganites; and appropriate substitution proportion would generate large MR near room temperature.     

Effect of Various Field Shapers on Magnetic Pressure in Electromagnetic Inward Tube Forming

In this paper,the influence of various field shapers and their shapes on the distribution of the magnetic flux densities and applied forces on the work-piece in the electromagnetic inward tube forming are studied numerically using the FEA software MAXWELL.First the model was verified with experimental results and thereafter four kinds of field shapers(conical,cylindrical,concave and convex)were considered.Effects of their geometries,such as air gap between field shaper and tube work-piece,height of the step in single and multiple stepped field shaper on magnetic flux densities and magnetic pressures were studied.The results of this research can be applied to design field shaper,tube compression technology,and improve the efficiency of the coil.It is seen that magnetic force decreases if height of step in convex field shaper increases but effective forming region enlarges.Decreasing air gap has also a positive influence on magnetic field increase.Though the object of this research is limited to field shaper for inward tube forming,the results can also be applied to the field shaper for tube bulging.     

Effect of Magnetic Field on Synthesis of Nano-FeOOH by Low-Temperature Neutralization Method

Using XRD,TEM and VSM methods,the phase,morphology and magnetic property of iron hydroxide oxide(FeOOH)which has been prepared by low-temperature neutralization reaction under different magnetic fields were analyzed.It can be found that the magnetic field had a great influence on the product.Acicular goethite(α-FeOOH)was synthetized without magnetic field.When the magnetic flux density was increased to 0.1T,γ-FeOOH was obtained.If the magnetic field intensity was raised to 0.5T,the product was all composed ofσ-FeOOH.Moreover,the crystallization of FeOOH was greatly influenced by magnetic field as well.Thermodynamic calculation results show that the magnetic free energy of chemical reaction reached to more than hundreds KJ/mol when the magnetic field is applied.It meaned that the application of magnetic field was conducived to producing the products with higher susceptibility.Even under the low magnetic field,due to the stability of the reaction products was broken by the magnetic field,the magnetic free energy was also effective.     

Influence of a Pulse Magnetic Field on the Size and Distribution of Primary Si in Hypereutectic Al-23%Si Alloy

A pulse magnetic field(PMF)was applied on the hypereutectic A1-23%Si alloy of different temperature range(830-780℃,830-730℃,830-700℃,780-700℃,730-700℃)during its solidification processing.The influence of pulse magnetic field on the size and distribution of primary Si was studied.The results show that,the primary Si is very coarse strip,distributs non-unifromly and gathers at the edge of the sample when the alloy solidifies under the condition of no PMF.By applying PMF can significantly refine the primary Si,and make the primary Si distribute uniformly.There has no significant effect on the refinement of primary Si when PMF applied from 830℃to 780℃,indicating that PMF has no outstanding effect on the high temperature liquid metal.Applying PMF from 50℃above the liquidus to 30℃below the liquidus(i.e.from liquid to the initial nucleation stage)can get the best refinement result.The refining mechanism of the pulse magnetic field on the solidification structure of Ai-23%Si alloy was discussed,     

Preparation of Nanoscale Sm2Co17 Flakes by Ball Milling in Magnetic Field

A new preparation method of Sm2Co17 nanoflakes was investigated. Hard magnetic Sm2 Co17 nanoflakes with thickness of 20-100 nm were obtained by milling in heptane and oleic acid under a magnetic field of 1.5 T for 0.5-20 h. It was shown that higher anisotropic magnetic properties would be induced by the flake-shape anisotropy when the prepared Sm2 Colt particles are milled with a magnetic field. The magnetic anisotropy of flakes after being aligned under the magnetic field of 1.5 T could be further enhanced, and the value of （BH）m was 128 kJ · m a Both anisotropy and properties are better than those of the nano-particles milled without a magnetic field.     

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

The extraordinary colossal magnetoresistance (CMR) behavior in Mn-site doped system La0.67Ca0.33Mn1-xCrxO3(0.00≤x≤0.15) was reported. It 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.     

Morphology Change of Electrodeposited Calcium Phosphate Coating on Ti6Al4V Substrate Under High Magnetic Field

The present study reports on the growth of calcium phosphate coatings on Ti6A14V substrate by electrodeposition under high magnetic field.The electrodeposition is conducted by potentiostatic method on horizontal electrode whose roughness was modified to reach a value of 3μm.The coatings are obtained from an electrolyte containing calcium nitrate as the Ca²⁺source and ammonium phosphate as the P source with a Ca/P ratio equal to two.The LNCMI high field continuous magnet in a 170 mm bore with homogeneity of 600.10^-6in 1 cm³ has been used.The magnetic field with a magnitude up to 12 T is applied perpendicularly to the electrode surface.The surface morphology and chemical composition of the obtained coatings were characterized by 3D digital microscope and scanning electron microscopy associated with X-ray microanalysis（SEM-EDX）.The phase composition was analyzed by X-Ray diffraction.The presence of several crystalline phases comprising octacalcium phosphate and hydroxyapatite is obtained and magnetic field seems to change the relative importance of these phases.The coating morphology changes from belt shape crystallites to needle shape crystallites with high magnetic field superimposition without important modification of Ca/P ratio in the deposit.On the other hand formation of volcano-like structures due to the presence of hydrogen bubbles during deposition is considerably reduced in the presence of magnetic field.