Competition between Band Filling and Steric Effect in Ordered Double Perovskites Sr2- x Lax MnMoO6

The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2- x Lax MnMoO6 （0 ≤ x ≤ 1 ）. The compounds have a monoclinic structure （space group P21/n） and the cell volume expands monotonically with La doping. The Tc and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-x LaxMnMoO6 decreases only at low doping levels （x ≤0.2）; while at high doping levels （0.8≤x ≤1）, electrical resistivity tends to increase greatly. The resuits suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.     

Magnetic studies of GaN nanoceramics doped with 1% of cerium

The magnetization measurements of gallium nitride nanoceramics doped with 1% of cerium and sintered under various pressures were reported.It was found that GaN nanoceramics doped with cerium showed paramagnetic behavior in the wide temperature range.Nanoceramics of GaN with 1% of Ce(as undoped GaN) was diamagnetic one,but under certain temperature the paramagnetic properties started to dominate.This crossover temperature was nonlinearly dependent on the pressure applied during the sintering.The fitting of molar magnetic susceptibility allowed to estimate the Curie temperature,Curie constant and diamagnetic part of susceptibility.As it was found,all the samples showed the antiferromagnetic ordering with θp≈-1 K.Also,the effective magnetic moment was estimated for all of the samples.As a result,magnetic moments in terms of Ce ion were notably larger in comparison with those obtained within the Russell-Saunders cou-pling model.We suggested that it was the strong influence of amorphous shell which was rising with the pressure applied during the sintering.Finally,we presented dependences of magnetization as a function of applied field.All the samples manifested weak ferromagnetism at high temperatures and paramagnetic behavior in low temperature region.     

Collapse of charge ordering in Bi0.5Sr0.5MnO3 by cation disorder： a magnetic and structural investigation

The structure, transport, and magnetic properties of LaxBi0.5.xSr0.5MnO3 （LBSMO） （x=0.1 and 0.4） were studied through X-ray diffraction, magnetization, and electron spin resonance （ESR） measurements. The structural analysis showed that the LBSMO crystallized in an orthorhombic perovskite structure with Pbnm space group for x=-0.1 and Imma space group for x=0.4 and the highly polarizable 6s^2 lone pair of Bi^3＋ was the ttming factor for the structural variations. Magnetic studies revealed that the replacement of Bi ions by La ions resulted in the collapse high temperature charge ordering state of BSMO and it order Ferro Magnetically （FM） with Tc around 355 and 330 K for x=0.1 and 0.4, respectively. Both ESR, temperature and field dependant magnetization suggested that there was a coexistence of FM and the paramagnetic phases well below Tc and the FM and CO-AFM phases below 250 K of LBSMO.     

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 and superconducting properties in Y0.6Gd0.4Ba2（Nb）Cu3O7-y cuprates doped with niobium

Polycrystalline YBa2Cu3O7-y (YBCO) and Y0.6Gd0.4Ba2-xNbxCu3O7-y (YGBNCO) compounds with 0≤x≤0.225 were synthesized using standard solid state reaction technique. The structure for all samples was characterized by X-ray difference (XRD) and scanning electron microscopy (SEM). The transport properties were measured by the (FPP) method in the temperature range from 70 to 130 K. As the Nb content in the samples increased, a diffused phase indicating a niobium perovskite phase and a small amount of unidentified phase appeared. With the increase of Nb content, the superconducting transition temperature Tconset increased slowly with x≤0.125, and then it remained unchanged or slowly decreased with 0.125≤x≤0.225. It could be found that there was a slow decrease of zero-resistance temperature, Tcoffset, with the increase of Nb content. The larger transition width might result from the YBa2NbO6 phase, impurity and unidentified phases of the sample due to the Nb doping.     

Co-substitution of zirconium and neodymium on hyperfine interactions and AC susceptibility of SrFe_(12)O_(19) nanohexaferrites

This study presents the influence of Zn and Nd co-substitution on structure,morphology,AC susceptibility and ZFC-FC magnetizations of Sr nanohexaferrites(NHFs),SrFe_(12-x)(Zn,Nd)_xO_(19)(0.0≤x≤1.0),which was produced by sol-gel approach.XRD powder patterns,scanning electron microscopy(SEM) and high-resolution transmission electron spectroscopy(HR-TEM) approve the synthesis of Sr M-type hexaferrite.Mossbauer spectra show that Zn~(2+)ions occupy 2 b and 4f_1 sites while Nd~(3+)ions locate at 2 a,4f_2 and 12 k sites.The magnetic properties of the produced Sr-NHFs were investigated also by ZFC-FC magnetizations and AC susceptibility.According to the M_(FC)-M_(ZFC) results(between 2 and 400 K),no blocking temperature was detected which indicates the ferromagnetic(FM) behavior of NHFs.At lower temperatures,a super-spin glass like behavior is discerned.The AC susceptibility indicates that the magnetic interactions are improved due to the inclusion of low content(x=0.1) of Nd~(3+)and Zn~(2+)ions into the Sr-NHFs.However,with further increasing the Nd~(3+)and Zn~(2+)contents(x=0.9),the magnetic interactions are weakened.     

Variation of optimum yttrium doping concentrations of perovskite type proton conductors BaZrl_xYxO3-~ （0~~~_0.3） with temperature

A solid state reaction method was used to prepare the perovskite-structured compounds BaZrl-xYxO3-a （x=0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3）. The X-ray diffraction （XRD） pattern indicated that the target perovsldte phases were obtained. With increasing Y con- centration the unit cell parameters of BaZrl-xYxO3-a samples were expanded, and Y doping became more difficult. However, high synthesis temperature is helpful to promote Y doping. The SEM results showed that the samples exhibited poor sinterability with in- creasing Y-doping content. Thermal gravimetric （TG） curves analysis showed the more mass decreasing of BaZrl-xYxO3-a （0≤x≤0.3） samples at high temperature with more Y doping and more proton introducing. The electrochemical impedance spectra （EIS） of specimens showed that conductivities of BaZrl_xYxO3（0≤x≤0.3） increased with increasing temperature from 300 to 900 ℃ in wet air. At 900 ℃, the conductivity of BaZrl-xYxO3-a （0≤x≤0.3） first increased with increasing doped amount of Y, and reached the high- est value of 1.07x 104 S/cm when x was 0.2, then decreased gradually with further increasing Y content. At 600 ℃, BaZr0.75Y0.2503-a displayed the highest conductivity, while the conductivity of BaZro.rYo.303-a was the highest at 300 ℃. The results indicated that there should be an optimum Y doping concentration yielding the highest conductivity at a constant temperature, and the optimum Y doping concentration should increase in the humidity atmosphere as the temperature decreases. So increasing the Y-doping concen- tration is helpful to improve the conductivities of BaZrl-xYxO3-a materials at low temperature.     

Magnetic properties of melt-spun ribbons(Sm_(1-x)Zr_x)(Fe_(0.92)Ti_(0.08))_(10) with ThMn_(12) structure and their hydrides

The structure and magnetic hysteresis properties of the cast Sm_(1-x)Zr_x(Fe_(0.92)Ti_(0.08))_(10)(x = 0-0.3)alloys and melt-spun ribbons prepared from them were studied.In the cast alloy with x0.2, a considerable amount of the eutectic phase is found in the SEM micrographs.Analysis of the temperature dependences of the magnetic susceptibility and XRD patterns allows amorphous state in the as-spun ribbons with x0.2 to be determined.The specific magnetization measured in a field of 17 kOe and remanence decrease with increasing annealing temperature from 800 to 900 ℃ and weakly depend on Zr concentration.The maximal value of coercivity Hc = 4.7 kOe is obtained on the ribbons with x = 0.2 after annealing at 850℃ for 10 min.After additional hydrogenation of the ribbons,both the coercivity and remanence increase by 54% and 7%,respectively.     

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.     

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.     

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.     

Effect of dopant concentration on the spectra characteristic in Zr~(4+) doped Yb:Nd:LiNbO_3 crystals

A series of Yb:Nd:LiNbO_3 crystals tridoped with various concentrations of Zr~(4+)(1 mol.%, 2 mol.% and 4 mol.%) were grown by the Czochralski technique from the congruent melt. The X-ray powder diffraction, UV-Vis-NIR absorption spectra and IR transmittance spectra were measured to analyze the crystal composition and defect structure. The Zr~(4+), Yb~(3+) and Nd~(3+) ions in LiNbO_3 crystal had two effects: volume compensation effect and ion valence state compensation effect. The Zr O2 doping threshold concentration was nearly 2.0 mol.%. The fluorescence emissions of Nd~(3+) ions and Yb~(3+) ions were observed under 808 nm excitation. The intensity of fluorescence emissions enhanced with the increasing of the Zr~(4+) doping concentrations. The Zr:Yb:Nd:LiNbO_3 crystals with 4 mol.% doping concentration of Zr~(4+) ion revealed strong emission around 1 μm, which is of great significance for laser materials.     

Effects of silicon content and intercritical annealing on the manganese partitioning in dual phase steels

 Steels of constant manganese and carbon contents with 0.34-2.26 wt. % silicon content were cast. The as-cast steels were then hot rolled at 1100°C in five passes to reduce the cast ingot thickness from 80 to 4 mm, air cooled to room temperature and cold rolled to 2 mm thickness. Dual-phase microstructures with different the volume fraction of martensite were obtained through the intercritical annealing of the steels at different temperatures for 15 min followed by water quenching. In addition of intercritical annealing temperature, silicon content also altered the volume fraction of martensite in dual-phase steels. The partitioning of manganese in dual-phase silicon steels were investigated using energy-dispersive X-ray spectrometry (EDS). The partitioning coefficient, defined as the ratio of the amounts of alloying element in the austenite to that in the adjacent ferrite, for manganese increased with increasing intercritical annealing temperature and silicon content of steels. It was also shown that the solubility of manganese in ferrite and austenite decreased with increasing intercritical temperature. The results were discussed by the diffusivity and the solubility of manganese in ferrite and austenite present in dual-phase silicon steels.     

Effects of Silicon Content and Intercritical Annealing on Manganese Partitioning in Dual Phase Steels

Steels of constant manganese and carbon contents with silicon content of 0.34%-2.26% were cast.The as-cast steels were then hot rolled at 1100 ℃ in five passes to reduce the cast ingot thickness from 80 to 4 mm, air cooled to room temperature and cold rolled to 2 mm in thickness. Dual phase microstructures with different volume fraction of martensite were obtained through the intercritical annealing of the steels at different temperatures for 15 min followed by water quenching. In addition to intercritical annealing temperature, silicon content also altered the volume fraction of martensite in dual phase steels. The partitioning of manganese in dual phase silicon steels was investigated using energy-dispersive spectrometer (EDS). The partitioning coefficient, defined as the ratio of the amounts of alloying element in the austenite to that in the adjacent ferrite, for manganese increased with increasing intercritical annealing temperature and silicon content of steels. It was also found that the solubility of manganese in ferrite and austenite decreased with increasing intercritical temperature. The results were discussed by the diffusivity and the solubility of manganese in ferrite and austenite existed in dual phase silicon steels.     

Local microstructure and photoluminescence of Er-doped 12CaO·7Al2O3 powder

Er-doped 12Ca0.7Al2O3 （C12A7：Er） powders were prepared using the sol-gel method followed by annealing inorganic precursors. X-ray diffraction （XRD）, Raman and absorption spectra revealed that Er ions existed and substituted Ca^2＋ lattice site in C12A7. The photoluminescence of C12A7：Er at room temperature was observed in the visible and infrared region using 488 nm （2.54 eV） Ar^＋ line as excitation source, respectively. The sharp and intense green emission bands with multi-peaks around 520 nm and 550 nm correspond to the transitions from the excited states ^2H11/2 and ^4S3/2 tO the ground state ^4I15/2, respectively. Furthermore, red emission band around 650 nm was also observed. It was attributed to the electronic transition from excited states ^4F9/2 to the ground state ^4I15/2 inside 4f-shell of Er^3＋ ions. The intensive infrared emission at 1.54 μm was attributed to the transition from the fast excited states of ^4I13/2 to the ground state （^4I15/2）. The temperature dependent photoluminescence of infrared emission showed that the integrated intensity reached a maximum value at near room temperature. The forbidden transitions of intra-4f shell electrons in free Er^3＋ ions were allowed in C12A7 owing to lack of the inversion symmetry in the Er^3＋ position in C12A7 crystal field. Our results suggested that C12A7：Er was a candidate for applications in Er-doped laser materials, and full color display.     

Crystal structure and hard magnetic properties of TbCu_7-type Sm_(0.98)Fe_(9.02–x)Ga_x nitrides

The compound Sm0.98Fe9.02–xGaxNδ(x=0, 0.25, 0.5, 0.75, 1) were prepared by melt-spun method and subsequent annealing and nitriding. The Rietveld analysis showed that the lattice expansion played an important role in improving the Curie temperature. An obvious development of the Curie temperature was obtained with the increased Ga content from x=0–1(ΔTc=90 oC). The optimum coercivity of nitrides was obtained at x=0.25 with the value Hcj=652 kA/m(8.15 kOe) after annealing, which corresponded to a reasonable distribution of grain sizes of both TbCu7-type SmFe9Nδ and α-Fe. However, an excess of Ga doping might lead to an abnormal growth of α-Fe, which in turn deteriorated the magnetic properties. It was concluded that a moderate Ga content was very effective in raising the coercivity and Curie temperament in the TbCu7-type Sm-Fe-N.     

Formation of AlN Nano Particles Precipitated in St-14 Low Carbon Steel by Micro and Nanoscopic Observations

In low carbon steels, dissolution and precipitation of the second phases such as carbides and nitrides during annealing cycles can affect the final structure and properties of the materials. The interaction of above processes depends on parameters such as reheating temperature, heating rate, annealing temperature, soaking time and finishing temperature in hot rolling stage before cold rolling. The effects of heating rate and annealing temperature on the microstructure and hardness were investigated. Two heating rates for annealing temperatures of 550, 610 and 720℃ were applied on cold-rolled specimens and St-14 low carbon steel, which were immediately quenched after isothermal annealing. The intercept method was used tO measure average grain sizes. However, resulted microstructures are dif- ferent for the two heating rates. While pancaked structures were observed in specimens annealed with low heating rate, in samples annealed with high heating rate, equiaxed microstructures were observed. Vickers micro-hardness values decreased at all temperatures, which were more significant at higher temperatures. At longer annealing time, signs of increase of hardness values were detected. All results and observations consistently suggest that a precipitati- on process has occurred concurrently with restoration processes during annealing. In addition, the energy dispersive spectroscopy analysis resulted from transmission electron microscopic micrographs have proved that the nano particles precipitated in grain boundaries are AlN.     

Effects of manganese doping on magnetocaloric effect in Ge-rich Gd_5Ge_（2.05）Si_（1.95） alloy

The structure, magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy, X-ray powder diffraction, differential scanning calorimeter (DSC) and magnetization measurements. The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired. DSC measurements were performed to determine the transformation temperatures for each alloy. Both alloys exhibited the first order phase transition around room temperature. The alloys showed an anti-ferromagnetic transition around 60 K. The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation. The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T, respectively.     

Paramagnetic Anisotropy of CdGd2（WO4） 4-δ Single Crystal

CdGd2 （WO4）4 -δ single crystal was grown using the Czochralski＇s method. The crystal structure was tetragonal seheelite with lattice parameters a = b = 0.5203 nm and c = 1. 1359 nm. There were vacancies of （WO4）^2- , therefore, there were some Gd^2＋ ions. Langevin paramagnetism and anisotropy were observed from the δ-T curves at room temperature. The susceptibility X//was 3.5018×10^-3, and X⊥ was 3.4403× 10^-2. The anisotropy was also observed in the electron spin resonance （ESR） experiments. The anisotropic Land6 factors were g//= 2. 1333 and g~ = 2. 8411. The direction of easy magnetization was in the α-b plane. Anisotropic paramagnetic Curie constants C//and C⊥ were not only related to macroscopic a that was observed through the experiment, but were also related to J⊥ and J//, which were the microscopic quantum numbers of the Gd^2＋ and Gd^3｜ ions. Based on the detailed analyses, the proportion of 36.8% of Gd^3＋ ions to 63.2% of Gd^2＋ ions in the Gd ions of the CdGd2（WO4）4-δ crystal was calculated, and δ was 0.638 in the single crystal.     

Magnetic properties and magnetic exchange interactions in Gd_(1–x)RE_x(RE=Pr,Nd) alloys

The effect of Pr,Nd addition on the magnetic properties and magnetic exchange interaction of gadolinium alloys was systematically studied.Curie temperature T_C and magnetic moment of Gd_(1–x)RE_x(RE=Pr,Nd)systems with x0.05 were investigated.When x0.05,Pr and Nd formed respectively with Gd continuous solid solution which has the crystalline structure HCP.Study on the magnetic behavior indicated that at near room temperature,the simple ferromagnetism prevailed in these two systems of alloy.The Curie temperature and magnetic moment of Gd_(1–x)RE_x alloy decreased with RE(RE= Pr,Nd)content x increasing.The de Gennes factor of Gd_(1–x)RE_x alloy which was associated with the exchange interaction between magnetic spin components also decreased with RE content increasing.The above results showed that the magnetic exchange interaction between magnetic atoms in gadolinium could be effectively changed by the Pr,Nd addition.