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.     

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,     

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.     

Magnetic and electric characteristics and abnormality of low-temperature resistivity in La0.67-xErxSr0.33MnO3(0.00≤x≤0.20) system

M-T curves, p-T curves, and MR-T curves of La0.67-xErxSr0.33MnO3 (x=0.00, 0.10, 0.20) system were studied by experiments. The experiments showed that: with increasing the doping amount, the magnetic structure of the system transformed from long-range ferromag-netic ordering to spin-cluster glass state, and M-T curves bent up in the extremely low temperature range; the resistivity of the system in-creased with increasing doping amount and exhibited the minimum phenomenon of low-temperature resistivity. The variation of the mag-netic and electric properties came from the extra magnetic coupling induced by the doping and from the Kondo effect induced by the lattice distortion and local magnetic moments which was similar to that induced by the mattering of magnetic impurities on electron spins.     

Transport and Magnetic Properties of Nanosized La0.6Sm0. 1Sr0.3MnO3 ＋ xCoO Composites

The composites La0.6Sm0.1Sr0.3MnO3 xCoO (x=0.0, 0.1, 0.2, 0.3, 0.4 mol), named as Ax samples, were synthesized by the sol-gel technique to derive homogeneous CoO-coated composites. CoO addition induces an increase of resistivity (ρ) and a decrease of Curie temperature (TC), magnetization, and TP at which the ρ peak is located. It has been concluded that the resistivity below TP fits well with the equation ρ=ρ0 ρ2T2 ρ4.5T4.5, indicating the importance of grain/domain boundary effects, the electron-electron scattering process, and the two magnon scattering process. On the other hand, the paramagnetic insulating region may be explained by using adiabatic small polaron hopping mechanism, thereby indicating that polaron hopping might be responsible for the conduction mechanism. Magnetoresistance results were explained by a two-level model of tunneling MR and percolation model.     

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.     

Structural,magnetic and electrical characterization of the La0.7Ca0.3Co1–xMnxO3（x=0,0.7 and 1） compounds prepared by a simple method

Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3（x=0, 0.7 and 1） samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3（LCCO） and La0.7Ca0.3Co0.3Mn0.7O3（LCCMO） samples to orthorhombic for La0.7Ca0.3MnO3（LCMO） sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic（PM） to ferromagnetic（FM） phase at Curie temperature, TC~155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample,clear evidence of spin glass（SG） state was observed at low temperature. PM-FM phase transition at about TC~260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator（MI） transition at about TMI~263 K, corresponding to Curie temperature. Metallic region of ρ（T） curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.     

Preparation and Electrical Transport Properties of Perovskite Oxide Ln0.5Sr0.5CoO3

The superfine powders of Ln0.5 Sr0.5 CoO3 （Ln = La, Pr, Nd, Sm, Eu） were obtained by solid state reactions. The crystal structure and electrical transport properties of samples doped with different rare earth elements as well as the forming process of the Perovskite structure were studied. The result shows that when the temperature reaches 1200 ℃, the samples will become a steady and unitary Perovskite phase by solid state reactions. The conductive behavor at low temperature is consistent with small polaron mechanism （i. e., localized electronic carriers having a thermally activated mobility）. However, the maximum of conductivity appears at about 700 ℃, and the conductivity of La0.5Sr0.5CoO3 is the biggest in the intermediate-temperature （600 - 850 ℃ ）, so it is fit for cathode material of intermediate-temperature solid oxide fuel cells.     

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 Co^3＋ and Co^4＋ ions should be in IS state after annealing and the oxygen annealing causes the transition of Co^3＋ spin state from HS to IS.     

Magnetocaloric effect in ErNi_2 melt-spun ribbons

ErNi2 ribbons were produced by rapid solidification using the melt spinning technique.Their structural,magnetic and magnetocaloric properties in the as-solidified state were studied by X-ray diffraction,scanning electron microscopy,magnetization and specific heat measurements.Samples are single phase with the MgCu_2-type crystal structure,a Curie temperature T_C of 6.8 K and a saturation magnetization at2 K and 5 T of 124.0 A·m~2/kg.For a magnetic field change μ_0△H of 5 T(2 T) ribbons show a maximum magnetic entropy change |△S_M~(peak)| of 24.1(16.9) J/(kg·K),and an adiabatic temperature change △T_(ad)~(max) of8.1(4.4) K;this is similar to the previously reported literature for bulk alloys that were processed through conventional melting techniques followed by prolonged thermal annealing.In addition,the samples also show slightly wider △S_M(T) curves with respect to bulk alloys leading to a larger refrigerant capacity.     

Microstructure of Sm-Fe Films Electrodeposited in a High Static Magnetic Field

Sm-Fe alloy films were electrodeposited in a high static magnetic field with the magnetic flux is perpendicular to the electric current.The samples were prepared on Cu substance in an aqueous solution by constant voltage method.The magnetic flux density used in the experiments were 0 T,2 T and 4 T,respectively.The microstructures,preferential orientation,composition of samples were characterized by SEM(equipped with EDS),AFM and XRD,respectively.The results showed that the thickness of films increased,whereas the concentration of Sm in films ascended first and then descended with the increasing of the flux density.The crystal grains were coarsened under the magnetic fields.The morphology of grains changed from granular at 0 T,to rough at 2 T and to cauliflower like at 4 T.The AFM results confirmed the different roughness of samples.However,the external field has not influenced the orientation of samples significantly.     

Magnetic properties and magnetic entropy change of perovskite manganites La_(0.9-x)Eu_xSr_(0.1)MnO_3(x=0.000,0.075) by experimental method and numerical fitting

Polycrystalline samples La_(0.9-x)EuxSr_(0.1)MnO_3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively; the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△S_M| value of the samples is near the Curie temperature(Tc), and the value of|△S_M| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T 77 K).     

Influence of partial substitution of cerium for lanthanum on magnetocaloric properties of La_(1–x)Ce_xFe_(11.44)Si_(1.56) and their hydrides

The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.     

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.     

Magnetocaloric properties,microhardness and corrosion resistance of Gd_(100–x)Zr_x alloys

With the intention to improve its mechanical properties and corrosion resistance,the magnetocaloric metal Gd was alloyed with Zr by arc melting and heat treatment.All Gd_(100-x)Zr_x(x=0,0.5,1,1.5,2) alloys with various Zr dopings showed hexagonal crystal structure.The Curie temperatures(TCs) of Zr doped alloys were lower than that of Gd by ~2 K.The maximum magnetic entropy changes of Gd_(99.5)Zr_(0.5) alloy under magnetic field changes of 0-2 T and 0-5 T were 5.27 and 9.41 J/(kg·K),respectively,which were larger than that of pure Gd metal.The addition of a small amount of Zr increased the microhardness of Gd by at least 29.3%.The corrosion resistance of Gd was also improved by Zr doping,demonstrated by increased corrosion potential and reduced corrosion current density in electrochemical polarization curves measurements.These enhanced properties were beneficial to the potential applications of Gd_(100-x)Zr_x alloys as magnetic refrigerants at room temperature.     

Effect of niobium addition on magnetization reversal behavior for SmCo-based magnets with TbCu7-type structure

The effect of Nb addition on the microstructure and magnetic properties of nanocrystalline Sm(CobalNbxZr0.02)7 permanent magnet were investigated. The magnetization reversal behavior for ball milled Sm(CobalNbxZr0.02)7 samples with high coercivity was investigated by analyzing hysteresis curves and recoil loops of demagnetization curves. Nb addition proved to result in relevant improvement in the magnetic properties, especially in the coercivity Hc. It was shown that the magnetic properties of Sm(CobalNbxZr0.02)7 nanocrystalline magnets were improved by an additional 0.06 at.% Nb. In particular, Hc was improved from 602 to 786 k A/m at room temperature. The maximum value of the integrated recoil loops area for 0.06 at.% Nb-doped samples of 1.81 k J/m3 was much lower than that of the Nb-free sample, which could be explained by a smaller recoverable portion of the magnetization remaining in the Nb-doped sample when the applied field was below the coercivity Hc. The nucleation field Hn for irreversible magnetization reversal of the magnetically hard phase were calculated by analyzed in terms of the ΔMirrev-H curve and the Kondorsky model.     

Hydrothermal Synthesis of Nano Ba-Ferrite With Additional High Pressure Under the Magnetic Field

The pressure of hydrothermal system is increased based on the traditional hydrothermal synthesis to prepare nano-barium ferrite at the reaction temperature of 180℃under different magnetic field.Using XRD,SEM and TEM methods,the phase composition and micro structure of the nano-barium ferrite powder obtained under different initial pressure（l.0atm,1.5atm and 2.0atm）is discussed.All the powder prepared under different initial pressure is mainly composed of BaFei₂O₁₉.But the morphology of the products is different.Flake BaFe₁₂O₁₉is obtained under the 10T magnetic field when the initial pressure is 1.5atm and 2.0atm.Moreover,the degree of crystallinity of hydrothermal products is also improved by the application of magnetic field and additional high pressure.Hexagonal flake grains of BaFei₂O₁₉with excellent crystallization have been prepared under 6T magnetic field,when the initial pressure reached2.0atm,some of the rod-like BaFe₁₂O₁₉self-organized to form ordered forked structure through oriented attachment due to the multiple influence of pressure and magnetic field on crystal face energy.It can be found that the additional high pressure will disturb the influence of the magnetic field on one-dimensional growth.And the phenomenon of oriented attachment can be regarded as the intermediate state between the one-dimensional rod and two-dimensional sheet.     

Microstructure and electrical resistivity in the GdNi_(5–x)Cu_x intermetallic series

The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi_(5–x)Cu_x series was studied. The value of temperature of phase transition(T_(ph)) estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K(x=0.0) to 29.1 K(x=5.0). The value of residual resistivity(ρ_o) estimated at low temperature range decreased from 27.28 μΩcm(x=0.0) to 9.44 μΩcm(x=5.0), which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity ρ(T) a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within ρ(T) curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds(x=4.8, x=5.0), which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.     

Effects of Sm-doping on microstructure,magnetic and microwave absorption properties of BiFeO_3

In this paper,polycrystalline samples of Bi_(1-x)Sm_xFeO~3(x=0,0.05,0.1,0.15) were successfully synthesized by sol-gel method.The effects of Sm concentration on the crystal structure,morphology,chemical states,magnetic properties and microwave absorption performance were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),a vibrating sample magnetometer(VSM) and a Vector network analyzer(VNA),respectively.The results show that the rare earth Sm doping causes the crystal structure to change.When x≤0.1,Bi_(1-x)Sm_xFeO_3 is the distorted rhombohedral structure with space group R3 c.With the increase of Sm doping amount to x=0.15,the phase structure of Bi_(1-x)Sm_xFeO_3 changes from rhombohedral structure to cubic structure with the space group Pm3 m.The particle size decreases with the increase of the Sm doping amount.The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties.The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi_(1-x)Sm_xFeO_3 powders.When Sm doping amount of x is 0.1,the Bi_(0.9)Sm_(0.1) FeO_3 compound has good microwave absorption performance,and the minimum reflection loss value of Bi_(0.9)Sm_(0.1)FeO_3 powder reaches about-32.9 dB at11.7 GHz,and its effective absorption bandwidth(RL -10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.     

Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

The effects of Sm on the microstructure and mechanical properties of Mg-11 Gd-2 Y-0.6 Al alloy were investigated by X-ray diffraction,optical microscopy,scanning electron microscopy,energy dispersive spectrometry and high resolution transmission electron microscopy.Based on the theory of edge—edge matching and electronegativity theory,the mechanism of grain refinement is discussed.The strengthening mechanism is expounded conveniently from fine grain strengthening,coherent strengthening,precipitation strengthening and grain boundary strengthening.The results show that the micro structure of Mg-11 Gd-2 Y-0.6 Al alloy is mainly composed of a-Mg matrix,Mg_5 Gd and Mg_(24)Y_5 phases.The addition of Sm forms Mg_(41)Sm_5 phase in the alloy and refines the alloy.The addition of Sm significantly improves the mechanical properties of the alloy at room and high temperatures.When the addition of Sm is 3 wt%,the tensile strengths of the alloy at room temperature and high temperature(200℃) reach the maximum value 292 and 321 MPa,respectively.The fracture mode of the alloy at different temperatures is mainly brittle fracture and intercrystalline fracture.