Magnetic properties of Pb2Sr2PrCu3O8

The magnetic properties of Pb₂Sr₂PrCu₃O₈ were determined using X-ray absorption, inelastic neutron spectroscopy and magnetic susceptibility measurements. X-ray absorption on the Pr L₃-edge strongly indicates a trivalent oxidation state. Inelastic neutron scattering results are modeled assuming a ³H₄ ground-state multiplet split by a crystalline electric field potential similar to PrBa₂Cu₃O_x. This potential correctly predicts the value of the Curie–Weiss moment, 2.72 μB, obtained from magnetic susceptibility measurements, and so explains the reduction from the free-ion value. The very broad magnetic response found in the inelastic neutron scattering experiments indicates a strong interaction between the Pr 4f electrons and the CuO₂ bands.     

Characterization of crystal field and nuclear quadrupole interactions in the D1 state of Am in LaCl3 and CaWO4

The crystal field splitting and hyperfine energy level structure in the first ⁵D₁ excited state of ²⁴³Am³⁺ in LaCl₃ and CaWO₄ have been studied using selective laser excitation, Zeeman and spectral hole burning experiments. Two crystal field levels and associated vibronic structures were observed in the electric dipole forbidden ⁷F₀↔⁵D₁ transition, that has a very weak magnetic dipole moment. The hyperfine energy level structure, including nuclear quadrupole splitting, was resolved in spectral hole burning studies. The existing free ion and crystal field interaction model provides a consistent interpretation of the observed ordering of crystal field levels and the magnitude of the nuclear quadrupole splitting of ²⁴³Am³⁺ in CaWO₄, whereas a discrepancy between the model and experimental results is encountered for ²⁴³Am³⁺ in LaCl₃. A discussion on the relationship between nuclear quadrupole interaction and free ion modeling is given.     

Metamagnetic phase transitions in perovskite manganites

A detailed study of step-like metamagnetic transitions in polycrystalline Pr_0.75Na_0.25Mn_1 − xFe_xO₃ (0 ≤ x ≤ 0.30) is reported. It shows that the charge-orbit ordering antiferromagnetic (COOAF) phase in the phase-separated materials is responsible for the step-like metamagnetic transition with extremely sharp steps (width <0.01 T). The fraction of antiferromagnet II (AFII) with larger antiferromagnetic exchange interaction than COOAF is proved to be the effective factor of critical fields (H_c). A model of anisotropy barrier for up/down thermal blocking spins has been proposed to explain the sharp step-like transitions in polycrystalline manganites for the first time. The metamagnetic transitions at 2 K (below the spin blocking temperature T_B) and high temperatures are compared. Both sorts of metamagnetic transitions originate from COOAF phase. And the temperature is responsible for the difference between them.     

Vibrational spectroscopy and periodic DFT studies of LaMg2PdH7: A material with two types of hydride

The need for a safe, reliable and cheap method for hydrogen transportation has prompted an intense effort in the synthesis of novel hydrides. To direct the search for better materials, it is essential to understand the bonding present in these systems. A newly synthesized material is LaMg₂PdH₇ which is best formulated as {La³⁺}{Mg²⁺}₂{[PdH₄]⁴⁻}{H⁻}₃. Thus hydrogen is formally present both as a free hydride ion and also as a covalently bound ligand. The combination of inelastic neutron scattering (INS), infrared and Raman spectroscopies and periodic density functional theory (DFT) has been used to characterise the material. We find that the material is less ionic than Ba₂[PdH₄], which also contains [PdH₄]⁴⁻. The charges carried by both the coordinating and free hydrides are similar which hints at a degree of covalency in the interactions between the interstitial hydrides and the lanthanum and magnesium ions.     

Zeeman study of electronic Raman transitions in Nd2CuO4

We have measured electronic Raman transitions involving the ⁴I_9/2 and ⁴I_13/2 multiplets of Nd³⁺ in Nd₂CuO₄ single crystals as a function of magnetic field up to 14 T. To account for the main features of 4f excitations observed we have used a single-ion Hamiltonian including the crystal field potential, the exchange interaction Nd–Cu and a Zeeman term as well as standard second-order theory of Raman intensities.     

Location of deuteron sites in the proton conducting perovskite BaZr0.50In0.50O3−y

High-resolution neutron powder diffraction data have been collected on deuterated and dried samples of the perovskite BaZr_0.5In_0.5O_2.75 at 5 K and room temperature, respectively. Inspection of Fourier nuclear density maps for the deuterated phase have allowed the deuteron position to be refined on a 12h (1/2, y, 0) crystallographic site, with y = 0.217(4) yielding a chemically reasonable OD distance of 0.92(2) Å. Evidence for anisotropy of the deuteron position is also found consistent with a 24k crystallographic site (0.56, 0.21, 0) indicative of displacements of the ion towards neighbouring oxygen ions. The presence of static oxygen disorder in both the dried and deuterated samples is apparent from the structural analyses. Raman spectra confirm short range deviations from cubic symmetry for both dried and hydrated samples.     

Paramagnetic susceptibility simulations from crystal field effects on rare earth antimonates R3Sb5O12

The magnetic susceptibilities of polycrystalline rare earth antimonates R₃Sb₅O₁₂ (R=rare earth), with cubic structure, space group I43m (No. 217), where the point site symmetry of R is S₄, have been measured from 4.2 to 800 K. Using the wave functions and energy levels derived from standard free ion and crystal field parameters deduced from the analysis of the optical spectra of pure and/or doped Pr, Nd, Eu and Er compounds, the calculation of the temperature dependent paramagnetic susceptibility has been carried out according to the Van Vleck formalism. The same calculation through crystal field parameters resulting from the ab initio simple overlap model over the entire R₃Sb₅O₁₂ series has been performed. Curves of both kinds were very similar for each configuration, with the exception of those for the Pr compound. Very good agreements with experimental data are found, especially below around 400 K, even when the approximate D_2d (near S₄) potential is considered. The standard crystal field treatment of 4f^N configurations is shown to explain the magnetic properties of these compounds with no need to consider any sort of magnetic interaction between the magnetic ions.     

The high temperature phase transitions of orthorhombic La0.95MnO3

The high temperature phase transitions of orthorhombic La_0.95MnO₃ from room temperature to 1273 K were studied using high temperature XRD technique in air. Two-phase transitions were found in temperature ranges, 373–473 K and 973–1273 K, respectively. The crystal symmetry increases from orthorhombic to rhombohedral then cubic, while the second transition was not completed in the observation of the present study. The first transition could be due to the depression of Jahn–Teller distortion, while the second one could be caused by the ionic oscillation at high temperature. The lattice thermal expansion coefficients of rhombohedral La_0.95MnO₃ from 473 to 973 K were also calculated using lattice parameters.     

Subsolidus phase relations in the ZnO–MoO3–B2O3, ZnO–MoO3–WO3 and ZnO–WO3–B2O3 ternary systems

The subsolidus phase relations in the ZnO–MoO₃–B₂O₃, ZnO–MoO₃–WO₃ and ZnO–WO₃–B₂O₃ ternary systems have been investigated by the means of X-ray powder diffraction (XRD). There is no ternary compound in all the systems. There are five binary compounds and five tie lines in the ZnO–MoO₃–B₂O₃ system. This system can be divided into six 3-phase regions. There are three binary compounds and three tie lines in the ZnO–MoO₃–WO₃ system. This system can be divided into four 3-phase regions. There are four binary compounds and four tie lines in the ZnO–WO₃–B₂O₃ system. This system can be divided into five 3-phase regions. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn₃B₂O₆–ZnWO₄ pseudo-binary system has been constructed, and the result reveals this system is eutectic system. The eutectic temperature is 1007 °C and eutectic point component is 70 mol% Zn₃B₂O₆.     

Energy levels and crystal field calculations of Er in LaAlO3

Absorption and emission of Er³⁺ doped LaAlO₃ crystal was measured at room and at low temperature (10 K). Based on these experimental results preliminary crystal field calculations were performed. The energy levels of Er³⁺ in LaAlO₃ were well reproduced.     

Gd~(3+)/Ga~(3+)共掺杂石榴石型Yb_3Al_5O_(12)材料的制备及热物理性能

采用柠檬酸溶胶-凝胶法制备了Gd~(3+)/Ga~(3+)双掺杂的石榴石型Yb_(3-x)Gd_xAl_(5-x)Ga_xO_(12)固溶体陶瓷材料(x=0,0.1,0.2,0.3,0.4,0.5;YGAGO)。结果表明:Gd~(3+)/Ga~(3+)共掺杂的YGAGO保持了石榴石相结构;随着Gd~(3+)/Ga~(3+)掺杂量的增加,固溶体样品的衍射峰位整体向低角度偏移;SEM形貌表明Yb_3Al_5O_(12)材料的微观形貌由纳米级晶粒和高密度晶界构成;大离子Gd~(3+)与Ga~(3+)分别对Yb_3Al_5O_(12)晶体结构中Yb~(3+)与Al~(3+)晶格位的取代,不仅因引入的点缺陷明显降低了材料的热导率,同时还造成石榴石型Yb_3Al_5O_(12)晶体结构的松弛,利于热膨胀系数的提高。随着Gd~(3+)/Ga~(3+)掺杂量的增加,晶体中点缺陷浓度不断升高,声子平均自由程不断减小,使得YGAGO的热导率在x=0.5时达到最低值(λ=1.67W/(m·K),T=1273 K),热膨胀系数达到最高值(α_1=11.71×10~(-6)K~(-1),T=1273 K)。     

Submillimeter EPR spectroscopy of Van Vleck paramagnets holmium nicotinate dihydrate and KY3F10:Ho

Results of EPR measurements of the Van Vleck paramagnets (monoclinic holmium nicotinate dihydrate and activated cubic complex fluoride KY₃F₁₀:Ho³⁺) are presented. Spectra were taken with a wide-band spectrometer operating in the frequency range 65–535 GHz at liquid helium temperature for magnetic fields up to 1 T. Transformations of the hyperfine structure of the EPR spectra with the frequency of the radiation and the directions of the constant and alternating magnetic fields have been studied and compared with results of calculations based on a diagonalization of the complete electronic–nuclear Hamiltonian. Crystal field splittings between the ground and first excited singlets of 7.3 cm⁻¹ in holmium nicotinate and 5.8 cm⁻¹ in KY₃F₁₀:Ho have been estimated using extrapolations of the resonance frequency dependences on magnetic field to zero field strength.     

磁场作用下Cr7C3硬质相生长机制

将纵向磁场引入到Fe5铁基合金粉末的等离子弧堆焊过程中,通过磁场的作用影响堆焊层中硬质相的形态及分布.利用金相显微镜和X射线衍射研究堆焊层中硬质相Cr₇C₃的显微组织和取向行为.结果表明,具有顺磁性的硬质相Cr₇C₃在外加磁场的作用下进行形核及长大的过程中有明显的取向现象,在磁场电流为3 A时,堆焊层中硬质相的分布形态最佳,以细小的"六边形"为主,可以显著提高堆焊层的影响和耐磨性;硬质相的取向机理主要是高温的旋转取向和低温的择优取向.     

Luminescence and crystal field calculation of aragonite-type LaBO3:Eu

The luminescent properties of trivalent europium in the aragonite-type lanthanum borate have been analysed and the crystal field calculation is performed in the real C₈ symmetry. The set of 14 crystal field parameters reproduces 22 experimental levels with an r.m.s. deviation of 5.8 cm⁻.     

Raman scattering study of the lattice dynamics of β-Zn4−xCdxSb3

Micro-Raman scattering experiments have been performed on the ternary solid solution in the Zn₄Sb₃–Cd₄Sb₃ system. Ten samples were studied; their compositions go from Zn₄Sb₃ to Zn_3.1Cd_0.9Sb₃. The homogeneity of these samples was checked by X-ray diffraction and electron microprobe analysis. The corresponding lattice parameters were calculated and their concentration dependence exhibits a small negative deviation from Vegard's law between end members of the Zn₄Sb₃–Cd₄Sb₃ system.

Three peaks and one shoulder are easily observable in the Raman spectrum of β-Zn₄Sb₃. These peaks are still present when the zinc atoms are substituted by cadmium ones. As the intensities of the Raman lines were observed to be very sensitive to the direction of the microcrystallites, only the change of the position could be discussed. From these experiments, we can suggest that the peak at about 155 cm⁻¹ should imply essentially Sb–Sb bondings while the peaks at about 172 cm⁻¹ and 320 cm⁻¹ must also imply Cd–Sb and Zn–Sb bondings.     

Effects of ferrites on magnetic transport properties in La2/3Sr1/3MnO3/ferrites composites

Effects of soft-magnetic MnZn ferrite (Mn0.5Zn0.5Fe2O4, MZF) and hard-magnetic Ba ferrite (BaO·6Fe2O3, BaM) on the structure and magnetic transport properties of [La2/3Sr1/3MnO3] (LSMO)/(x) [ferrites] (ferrites=MZF, BaM) composites have been investigated. It was found that the inclusion of MZF phase reduces magnetization and ferromagnetic-paramagnetic transition temperature (Tc) of the composites. With increasing the content of the dopants, the high-temperature magnetoresistance (MR) decreases, whereas low-...     

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

The effect of LMO doping on the structure, magnetic and magnetotransport properties of La_0.8Sr_0.2MnO₃ (LSMO)/xLaMnO₃ (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SL_x (low temperature sintered samples) and SH_x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL_x samples and 0 ≤ x ≤ 10 for SH_x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.     

Study of structure and magnetic properties of the perovskite Tb0.5Sr0.5CoO3

The perovskite compound Tb_0.5Sr_0.5CoO₃ has been prepared and studied for the first time. We report here the structural and magnetic properties of the compound using the DC magnetization and powder neutron diffraction techniques. The compound is found to be orthorhombic with Pbnm space group. The magnetic ground state of the system is ferromagnetic with T_c = 120 K. The ordered magnetic moment is found to be 1.57 (4) μ_B/Co ion at 12 K along the crystallographic b-axis. The observed effective paramagnetic moment μ_eff = 2.54 μ_B/f.u. The role of ionic size effect on the magnetic and transport properties of the compound through the variation of CoOCo bond angles is highlighted.