Effect of La–Zn Substitution on the Structure and Magnetic Properties of Low Temperature Co-Fired M-Type Barium Ferrite

Ba(LaZn) _x Fe_12?2x O₁₉ (0≤x≤0.5) powders with Bi₂O₃ as an additive was synthesized by a sintered route at 900 °C or 950 °C. The structure and magnetic properties of La–Zn substituted M-type barium ferrites were also investigated. When 0≤x≤0.5, only one crystal phase existed in the sample, and the morphology of the grains were shown to be gradually irregular. The little amount of La³⁺ ions and Zn²⁺ ions changed the equilibrium of Fe²⁺ and Fe³⁺ at the 2a site, which increased the Fe³⁺–O–Fe²⁺ superexchange interaction strength, and the saturation magnetization (Ms) of the samples was also improved. Meanwhile, the substitution of La³⁺ and Zn²⁺ ions and the grains’ size bought great effects on the magnetocrystalline anisotropy field. As a result, with sintering at 950 °C for 6 h, the max Ms value of the samples with x=0.1 was 67.26 emu/g, and the minimum coercivity (H _c ) value was 1718.89 Oe with x=0.3, respectively.     

Effect of Crystal Structure on the Electrical Properties of CaTi1 – xFexO3 – δ

The electrical conductivity of CaTi_{1 – x} Fe _x O_{3 –} (x= 0–0.5) was measured as a function of temperature and oxygen partial pressure. At 1000°C, the highest conductivity was observed at x= 0.2. The crystal structure of the materials with x= 0, 0.2, 0.25, and 0.3 was studied by x-ray powder diffraction and refined by the full-profile analysis method. The results were used to elucidate the mechanisms of the high-temperature (1000°C) formation, ordering, and transport of oxygen vacancies in CaTiO₃upon substitution of Fe³⁺for Ti⁴⁺. The composition dependences of ionic conductivity calculated for CaTi_{1 – x} Fe _x O_{3 –} agree well with experiment.     

Influence of Grinding Particle Size on Structure and Electrical Properties of La0.67Sr0.33MnO3−δ Compound

In this article, the influences of grinding particle size on the structure and electrical transport properties of La_0.67Sr_0.33MnO_3?δ compound have been investigated. The compound was prepared by gel combustion process followed by grinding for different duration time. It was found that the lattice parameters, unit-cell volume, strain, oxygen deficiency, and temperature dependence of resistivity ρ–T increase with decreasing particle size. The ρ–T growth can be explained by the increasing contribution of the grain boundary effect, strain, and even oxygen deficiency. The electrical transport mechanism over the whole temperature range of 100–400 K was thoroughly described by applying the phase separation model around the phase transition temperature T_P. This model was subsequently employed to calculate the ρ–T at high temperature up to 1000 K. The result showed there was a second phase transition at a typical temperature T*>T_P, which could be attributed to the relaxation of small polarons to large ones. This relaxation occurred at lower temperatures when the particle size decreased. It might be due to the decrease in conduction bandwidth caused by the defects arisen during the grinding.     

Effect of Composition Variations on Electrical and Optical Properties of La1−x (Ca, Sr) x MnO3 Thin Films

Thin films of La _0.67 Ca _0.33 MnO ₃₊ (d 200 nm) grown at 750° C on MgO(100) substrates by pulsed laser deposition were annealed in various oxygen atmospheres. The LaF ₃ , CaF ₂ and Mn overlayers (d 5-10 nm) have been evaporated onto the films in order to saturate the compound by La, Ca or Mn during subsequent annealing at 900° C in air. Further, the pulsed injection CVD method has been utilized to prepare series of La _1–x Sr _x MnO ₃ films with x = 0÷0.5 on LaAlO ₃ (100). The effect of composition variations on electrical resistivity and magnetoresistance of the films as well as on their optical transmission and reflection spectra in the energy range between 0.2 and 4.0 eV has been investigated.     

Effects of Bi Substitution on Magnetic and Transport Properties of La0.7?x Bi x Ag0.3MnO3 Ceramics

Colossal magnetoresistance, CMR ceramics with starting composition of La_0.7?x Bi _x Ag_0.3MnO₃ (x=0?C0.2) were synthesized using the conventional solid-state synthesis method to investigate the effects of Bi and Ag on their magnetic and electrical transport properties as well as their magnetoresistance behavior. Magnetic susceptibility measurements showed that the La_0.7?x Bi _x Ag_0.3MnO₃ samples with x=0, 0.10 and 0.15 exhibit single paramagnetic to ferromagnetic transition at Curie temperature, T _C , which was observed to decrease from 289.5?K (x=0) to 186.5?K (x=0.15) while the x=0.2 sample showed two magnetic transitions at T _C1 (160.5?K) and T _C2 (214.0?K). Electrical resistivity measurements showed metal?Cinsulator transition behavior for all samples. Bi substitution caused resistivity to increase while metal?Cinsulator transition temperature, T _MI shifted to lower temperature from 252.7?K (x=0) to 136.3?K (x=0.20). The metallic region of the ??(0,T) curve below T _MI for all samples was well fitted to the equation ??=?? _o +?? ₂ T ²+?? _4.5 T ^4.5 indicating a combination of grain or domain boundary, electron?Celectron and electron?Cmagnon scattering mechanism while the insulator region was governed by the Variable Range Hopping (VRH) model at T _MI<T<?? _D /2 and adiabatic small polaronic model (SPH) at T>?? _D /2. The increase of hopping activation energy, E _a for the latter is suggested to be due to possible hybridization between Bi 6s² lone pair and O orbital. Bi³⁺ substitution was also observed to enhance intrinsic MR at the vicinity of T _MI due to increase in DE interaction when external magnetic field was applied. On the other hand, the substitution also caused reduction of extrinsic MR effect at low temperatures, which is suggested to be due to reduction of Mn spin disorder at grain boundaries as a result of the presence of small amount of Ag secondary phase.     

Magnetic and Magnetocaloric Properties of La0.67Pb0.33?x Ag x MnO3 Compounds

In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganites La_0.67Pb_0.33?x Ag _x MnO₃ (0??x??0.15), which show a sharp paramagnetic-ferromagnetic phase transition over a wide temperature range (T=250?C401?K). The Curie temperature has been analyzed by two methods: using the numerical derivative dM/dT and the thermodynamic model. The experimental results indicate that T _C decreases from 368 to 288?K with increasing Ag substitution independently of the method used to obtain?T _C. Upon 10?KOe applied magnetic field, the large magnetic-entropy change (|??S _M|) reaches values of 2.75, 3, 3.25 and 3.5?J/kg?K for x=0, 0.05, 0.10 and 0.15 compositions, respectively, which are comparable to that of?Gd. The relative cooling power (RCP) increases with increasing Ag content from 68.75 (x=0) to 156.27?J/kg (x=0.15) for ??H=10?KOe. Through these results, La_0.67Pb_0.33?x Ag _x MnO₃ materials are strongly suggested for the use of active refrigerants for magnetic refrigeration technology near room temperature.     

Effect of Doping and High-Temperature Annealing on the Structural and Electrical Properties of Zn_(1-X)Ni_XO(0≤X≤0.15) Powders

This paper reported the synthesis,crystal structure and electrical conductivity properties of Ni-doped ZnO powders(i.e.Zn 1 X Ni X O binary system,X=0,0.0025,0.005,0.0075 and in the range 0.01≤X≤0.15).Iphase samples,which were indexed as single phase with a hexagonal(wurtzite) structure in the Zn 1 X Ni X O binary system,were determined by X-ray diffraction(XRD).The widest range of the I-phase was determined as 0≤X≤0.03 at 1200 C;above this range the mixed phase was observed.The impurity phase was determined as NiO when compared with standard XRD data,using the PDF program.We focused on single I-phase ZnO samples which were synthesized at 1200 C because of the widest range of solubility limit at this temperature.It was observed that the lattice parameters a and c of the I-phase decreased with Ni doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The electrical conductivity of the pure ZnO and single I-phase samples were studied by using the four-probe dc method at temperatures between 100 and 950 C in air atmosphere.The electrical conductivity values of pure ZnO and 3 mol% Ni-doped ZnO samples at 100 C were 2×10 6 and 4.8×10 6 1 ·cm 1,and at 950 C they were 1.8 and 3.6 1 ·cm 1,respectively.In other words,electrical conductivity increased with Ni doping concentration.     

Effect of CuO Addition on the Sintering Behavior and Electrical Conductivity of 3Y-TZP

Yttria stabilized tetragonal zirconia polycrystals （3Y-TZP） doped with CuO was prepared, to get two compositions, 0.3 and 1 mole fraction CuO, respectively. The dilatometric study of the samples showed sintering to be improved for the samples doped with 0.3 mole fraction CuO, and to be deteriorated for the samples doped with 1 mole fraction CuO. The 1 mole fraction CuO doped 3Y-TZP showed higher tetragonal/monoclinic phase transformation which was accompanied by grain growth. The electrical conductivity decreased with the addition of CuO.     

Effect of Vacuum and O2 Annealing Treatments on Structural and Magnetic Properties of La0.5Ca0.5MnO3 Thin Films

La_0.5Ca_0.5MnO₃ films with a nominal thickness of 80 nm were epitaxially grown on (001) SrTiO₃ and SrLaAlO₄ substrates by the pulsed laser deposition technique. The magnetic moment of the films was observed to depend strongly on the oxygen stoichiometry, tuned by heat treatments in vacuum and O₂ environments. A distinctly larger out-of-plane lattice parameter was measured for the vacuum-annealed films due to transformation of some Mn⁴⁺ ions to Mn³⁺. Both the variations in the magnetic moment and out-of-plane lattice parameter during vacuum annealing can be recovered by subsequent heat treatments in O₂ environment. In this study, it is shown that the enhancement of the magnetic moment via O₂ annealing is considerably less prominent than the respective improvement obtained by the application of compressive epitaxial strain.     

Effect of Boron Substitution for Bi on Superconductivity of the Bi-2212 Phase in the Bi-Sr-Ca-Cu-O System

Possibility of boron substitution for Bi and the substitution effect on superconductivity is investigated for the Bi-2212 phase of Bi-Sr-Ca-Cu-O. From X-ray diffraction study, it is found that samples in the (Bi_2?x B _x )Sr₂CaCu₂O _z system are mainly of the single 2212 phase in a composition range of 0.0≤x≤0.6, and both of the lattice parameters a and c change with increasing x up to 0.6. From measurements of the magnetic susceptibility and the electrical resistivity, the superconducting transition temperature is found to increase up to 0.6 with increasing x. These results are considered to show that boron is substitutable for Bi up to x=0.6 in the (Bi_2?x B _x )Sr₂CaCu₂O _z system and that the boron substitution causes the number of hole-carriers to decrease in this system.     

The Tb Doping Effect on the Room Temperature Magnetoresistance in (La1-xTbx)0.67Sr0.33MnO3 (x≤ 0.4)

by Tb in (La1-xTbx)0.67Sr0.33MnO3, the room temperature magnetoresistance △R/R0 drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperature magnetoresistance at a field H=12 kOe for (La1-xTbx)0.67Sr0.33MnO3 is -3.56%. The enhancement of the room temperature magnetoresistance induced by an appropriate Tb substitution in (La1-xTbx)0.67Sr0.33MnO3 is correlated with the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop of the room temperature magnetoresistance at large Tb doping-contents may be due to its lower TC and TMI far from the room temperature.     

The Influence of the Morphology on the Magnetic Properties of Poly(3-hexylthiophene)

The influence of the morphology on the magnetic properties of poly(3-hexylthiophene) has been studied and the results reported. The changes in the saturation magnetization were explained considering the polymer morphology prepared with different amounts of water in the solution during sample synthesis. The results show that the saturation magnetization is maximized for 200 ppm of the water in acetonitrile solution.     

Mechanical Alloying Effect on the Structure of Fe-Al-(Si) Alloy

The mechanical alloying effects on the structures of Fe71.3AI28.4(CeO2)0.3 and Fe73.3AI9.8-Si,e.e(CeO2)0.3 samples have been investigated mainly by Mossbauer spectroscopy and X-ray diffraction. It is found that with the increase of milling time, a substituting disordered a-Fe solution is formed gradually and almost completed after milled for 72 h. Further increasing milling time causes the atomic rearrangement within the powders. Correspondingly' the average lattice parameter and average crystalline size change until 72 h and remain constant after 72 h. The addition of Si leads to the higher disordered degree reflected in the smaller average hyperfine field and larger mean Square deviation.     

Structure and characterization of magnetoresistance of La0.7Pb0.3MnO3−δ in bulk and films deposited on LaAlO3 (100), (110) and (111) substrates

The structure and properties of La_0.7Pb_0.3MnO_3−δ (LPMO) bulk and films, which are deposited onto (001), (110) and (111) LaAlO₃ (LAO) substrates using the direct current magnetron sputtering technique, are obtained. For bulk of LPMO, T_p is almost equal to T_c (252 K) and its R(T) curve has a bump in low temperature region. For films, the colossal magnetoresistance (CMR) of 28% at 155 K and in 0.5 T was observed on (001) oriented substrate under 9 Pa sputtering gas pressure and substrate temperature of 790 °C. The transport properties of the deposited films are slightly lower than that of the bulk.     

Electrical Conductivity of Thin Polycrystalline La0.83Sr0.17MnO3 Films in Pulsed High Electric and Magnetic Fields

The electrical conductivity of thin polycrystalline La_0.83Sr_0.17MnO₃ films was investigated. These films were simultaneously affected by a single electrical pulse having a pulse length of several ns and a half-sinus magnetic pulse with a pulse length of 1 ms and amplitude ranging up to 20 T. The influence of the high magnetic field on the electroresistance was studied at electric field strengths up to 80 kV/cm when the temperature of the film ranged from 100 K to 300 K. It was found that depending on the temperature and magnetic field value the electroresistance (ER) can be enhanced or suppressed by the applied magnetic field. These results are explained by assuming that the ER appears due to inelastic multistep tunneling through grain boundaries and by taking into account the redistribution of voltage across crystalline grains and grain boundary regions.     

Effect of Thickness on the Structure and Tribological Properties of MoSx Coating

MoSx coatings were prepared by bipolar-pulse DC unbalanced magnetron-sputtering system with the variation of coating thickness at different Ar pressures.The composition and surface morphology were determined by using energy dispersive X-ray and scanning electron microscopy;the structural characterization was analyzed by X-ray diffraction.The friction and wear properties were investigated by fretting tests in air with less than 10% and 50% relative humidity.At 0.40 Pa pressure,(002) basal plane orientation was formed throughout the coatings.At 0.88 Pa and 1.60 Pa pressures,(002) basal plane orientation was only noticed in the first stage of coating growth(around 0.20 μm in thickness), and then edge orientations with their basal planes perpendicular to the surface would be evolved in the coatings.Humidity has a minor influence on the coatings that have(002) basal plane orientation,whereas the tribological properties of MoSx coatings with edge orientations are greatly affected by humidity.The mechanisms of coating growth and friction and wear processes are discussed.     

Effect of Fe and Co doping on electrical and thermal properties of La0.5Ce0.5Mn1−x(Fe,Co)xO3 manganites

The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La_0.5Ce_0.5Mn_1−x(Fe, Co)_xO₃ is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La_0.5Ce_0.5MnO₃ exhibits metal-semiconductor transition (T_MS at ∼225 K). However, La_0.5Ce_0.5Mn_1−xTM_xO₃ (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.