Electromechanical properties of Co0.6 Zn0.4 Fe2O4 ferrite transducer

Co_0.6Zn_0.4Fe₂O₄ ferrite has been prepared by the general ceramic method. The resonance frequency of the disk for the radial and thickness mode was investigated as a function of mechanical stress. The increase of the resonance frequency of the transducer is attributed to domain wall motion inhibition. The increase of ultrasonic velocity with increasing mechanical stress can be explained as due to retarding the oscillation of the ferrimagnetic domains under applied high-frequency electric field. The induced strain increases the resonance frequency. The high values of the electromechanical coupling factor for the radial mode K_p, and thickness mode, K_t, indicate that this composition is useful for producing high-frequency ultrasonic waves that can be used in modern technology.     

NMR on 55Mn in the ferromagnetic Ni-substituted manganite La0.6Pb0.4Mn0.86Ni0.14O3

NMR on ⁵⁵Mn in the single-crystal manganite La_0.6Pb_0.4Mn_0.86Ni_0.14O₃ (T _C =242 K), which exhibits metallic conductivity below T _C , is investigated in the temperature range 61–215 K. At low temperatures, together with a line corresponding to the averaged hyperfine field at the ⁵⁵Mn nuclei (the averaging is due to the motion of electronic holes along Mn sites), the NMR spectrum also contains two lines corresponding to localized states Mn⁴⁺ and Mn³⁺. In the temperature range 100–200 K it is found that the complicated NMR spectrum is transformed into a single line on account of a delocalization of the holes in the e _g orbitals of manganese. A comparison of the NMR data with the temperature dependence of the resistivity suggsets that a wide distribution of charge-carrier mobilities exists in the crystal. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 522–527 (25 October 1999)     

Evolution of the 251 cm-1 temperature in infrared phonon mode with Ba0.6K0.4Fe2As2

The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 em-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continu- ously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observa- tions indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Bao.6Ko.4Fe2As2 compound.     

Effect of manganese addition on physical properties of Co0.6Zn0.4MnxFe2-xO4 system

X-ray analysis and magnetic properties have been studied for the system Co_0.6Zn_0.4Mn_xFe_2-xO₄. The bulk density, X-ray density and porosity were also studied. It was found that the lattice constant decreased with increasing manganese concentration x. The X-ray density, the bulk density and porosity do depend on the manganese content. The magnetic susceptibility and the activation energies were found to be increased with increasing percentage of the manganese ions while the dc conductivity decreased.     

Effects of excessive Zn2+ ions on intrinsic magnetic and structural properties of Ni0.2Zn0.6Cu0.2Fe2O4 powder prepared by chemical coprecipitation method

Zn(OH)₂ is a kind of amphoteric compound. Therefore, for chemical coprecipitation method, the precipitation of Zn²⁺ ions may be incomplete if using NaOH as precipitator. In this study, single-phase powder specimens with a nominal composition Ni_0.2Zn_0.6Cu_0.2Fe₂O₄ were prepared with chemical coprecipitation method, and the effects of excessive Zn²⁺ content (x, x = 3%, 5%, 7%, 9%) in working solution on intrinsic magnetic and structural properties were studied by vibrating sample magnetometer and X-ray diffractometer, respectively. It was found that the magnetization when H_m = 398 kA/m (5000 Oe) reached a maximum when x = 5%, and then decreased with the increase of x, which was attributed to the effect of different amount of Zn²⁺ in A sites on the A–B and B–B exchange interaction. Moreover, it was found that the lattice parameter was affected by the Zn²⁺ and Fe³⁺ ions due to their different ion radius to a certain extent.     

Ni0.8Zn0.2Fe2O4和CO2Y添加Ni0.8Zn0.2Fe2O4磁性质对比研究

采用固相反应法制备了Ni0.8Zn0.2Fe2O4和2wt％ Co2Y添加Ni0.8Zn0.2Fe2O4铁氧体多晶样品,并对样品的磁性质进行了研究.实验发现,添加Co2Y后,铁氧体的磁损耗明显下降,相同条件下Q值增大到原来的3倍左右.对添加Co2Y引起铁氧体磁损耗下降的原因进行了讨论,认为主要是钴离子掺杂引起的铁氧体磁滞损耗明显降低所导致的.     

Static and dynamic behavior of the cluster phase in LaMn0.6Co0.4O3

A non-uniform magnetic state in the perovskite system LaMn_0.6Co_0.4O₃ has been studied by magnetometric methods. Two ferromagnetic (FM) critical temperatures are observed. The first one at T_C1≈217 K is ascribed to the onset of FM state in the Mn⁴⁺/Co²⁺-ordered domains (phase 1), while the disordered regions containing Mn⁴⁺, Mn³⁺, Co³⁺ and Co²⁺ valence states (phase 2) remain in the paramagnetic state. Below T_C2≈147 K a long-range FM arrangement develops also in certain part of phase 2, but the major part of phase 2 is formed by polydisperse FM clusters. This second transition is accompanied by a huge increase of coercivity and by occurrence of long-time relaxation. Finally, between 40 and 65 K, a frequency-dependent maximum in the imaginary part of the ac susceptibility is observed, which can be ascribed to the relaxation of small clusters behaving superparamagnetically.     

Pressure tuning of magnetic interactions in layered (La0.6Nd0.4)1. 2Sr1.8Mn2O7 manganite

The effect of pressure of up to 9 GPa on the magnetic and structural properties of layered (La0.6Nd0.4)1.2Sr1.8Mn2O7 manganite has been investigated. Pressure shifts the Mn atoms from the center of each bilayer towards the adjacent bilayer. The observed shift of the Mn atoms involves mainly a charge redistribution within the d(3z(2)-r(2)) axial orbital. The decrease in the interbilayer spacing and the shift of the Mn atoms away from the center of each bilayer result in increased magnetic and electronic coupling between the adjacent bilayers along the c axis.     

Influence of coated MnO2 content on the electrochemical performance of Li1.2Ni0.2Mn0.6O2 cathodes

Layered cathode material Li_1.2Ni_0.2Mn_0.6O₂ has been synthesized using a coprecipitation method and coated by MnO₂ with varying amounts (1, 3, 5, and 9 wt%). The physical properties and electrochemical performances of the materials are characterized by XRD, SEM, charge/discharge tests, cycle life, and rate capability tests. XRD patterns show that the pristine and coated Li_1.2Ni_0.2Mn_0.6O₂ powders exhibit layered structure. The discharge capacities and coulombic efficiencies of Li_1.2Ni_0.2Mn_0.6O₂ in the first cycle have been improved and increase with the increasing content of coated MnO₂. The 9 wt% MnO₂-coated Li_1.2Ni_0.2Mn_0.6O₂ delivers 287 mAhg^?1 for the first discharge capacity and 86.7 % for the first coulombic efficiency compared with 228 mAhg^?1 and 65.9 % for pristine Li_1.2Ni_0.2Mn_0.6O₂. However, the 5 wt% MnO₂-coated Li_1.2Ni_0.2Mn_0.6O₂ shows the best capacity retention (99.9 % for 50 cycles) and rate capability (88.6 mAhg^?1 at 10 C), while the pristine Li_1.2Ni_0.2Mn_0.6O₂ only shows 91.5 % for 50 cycles and 25.3 mAhg^?1 at 10 C. The charge/discharge curves and differential capacity vs. voltage (dQ/dV) curves show that the coated MnO₂ reacts with Li⁺ during the charge and discharge process, which is responsible for higher discharge capacity after coating. Electrochemical impedance spectroscopy results show that the R _ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode decreases after coating, which is responsible for superior rate capability.     

Superstructure of atomic displacements in cubic compounds Zn0.9Ni0.1S and Zn0.7Ni0.3O

The fine structure of cubic compounds Zn_0.9Ni_0.1S and Zn_0.7Ni_0.3O has been discussed. At room temperature, their diffraction patterns contain, along with intense Bragg reflections of the face-centered cubic phase, superstructure diffuse maxima demonstrating the ordering of short-wavelength deformations due to Jahn-Teller nickel ions.     

The superconducting properties of YBa2(Cu1−xMx)3O7 for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa₂(Cu_1−xNi_x)₃O_7−y withx=0.1 and 0.2, and YBa₂(Cu_1−x Zn _x )₃O_7−y withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs⁻¹.1.6μs⁻¹, and 1 μs⁻¹ forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs⁻¹, 0.75 μs⁻¹, 0.65 μs⁻¹, and 0.4 μs⁻¹ forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.     

Magnetic structure and properties of the Nd0.6Ca0.4Mn0.5Cr0.5O3 manganite

The effect of high chromium concentrations on the charge and orbital ordering in manganites is studied using neutron diffraction and magnetic measurements. It is found that the Nd_0.6Ca_0.4Mn_0.5Cr_0.5O₃ manganite exhibits a CE-type antiferromagnetic ordering with a weak ferromagnetic component below 160 K. In the Nd_0.6Ca_0.4Mn_0.5Cr_0.5O₃ manganite, the Mn and Cr ions form antiferromagnetic zigzag chains that are likewise antiferromagnetically coupled with one another in the basal plane and are arranged along the b axis of the orthorhombic structure with oppositely directed spins. An applied magnetic field of 5 T does not change the magnetic structure.     

Calculation of the vibronic spectrum of excitonic luminescence in AgBr:I

The radiative decay of an exciton bound to a substitutional iodine ion in AgBr is investigated theoretically. The vibronic spectrum showing multiphonon replicas is calculated under the assumptions of linear electron-phonon coupling. The experimental intensity of the one-phonon spectrum as a function of frequency could satisfactorily be reproduced only by considering coupling coefficients up to fifth neighbors. This result indicates that the bound exciton influences the dynamics of the lattice over an extended neighborhood of the iodine.     

Acousto-optical effect in the luminescence excitation spectrum of HgI2

A study of the photoluminescence excitation spectrum in a crystal of mercury diiodide is reported. Each of the two luminescence bands peaking at 543 and 572–575 nm investigated was found to have its own excitation spectrum. The excitation spectrum of the 575-nm line in the long-wavelength doublet band has been observed to be sensitive to strong ultrasound vibrations and preliminary irradiation of the sample by 590-nm light. This line is associated with radiative recombination of photocarriers at intrinsic point defects (vacancies or iodine and mercury interstitials) located close to dislocations. The binding energy of the photosensitive center to a dislocation was estimated from the change in the excitation spectrum. Fiz. Tverd. Tela (St. Petersburg) 41, 1965–1968 (November 1999)     

退火温度对Er/Yb共掺Al2O3薄膜的光致荧光光谱的影响

通过对不同退火条件下Er/Yb共掺Al2O3薄膜光致荧光(PL)光谱的系统分析,研究了高Er/Yb掺杂浓度所导致的晶体场变化对薄膜PL光谱的影响,并结合薄膜结构分析,探讨了Al2O3薄膜的结晶状态在Er3+激活、PL光谱宽化中的作用及可能的物理机理.研究结果表明:退火处理所导致的Er3+ PL光谱的变化与薄膜的微观状态之间有着密切的联系.在600-750℃范围内,薄膜呈非晶态结构,薄膜荧光强度的增加主要是薄膜内缺陷减少所致;在800-900℃范围内,γ-Al2O3相的出现是导致荧光强度明显增加的主要原因;当退火温度为1000℃时,Er,Yb的大量析出致使荧光强度的急剧下降.此外,对PL光谱线形分析表明,各子能级跃迁的相对强度变化是导致荧光光谱宽化的主要因素.     

Effect of neutron irradiation on the long-wavelength magnetic excitations in the Zn0.60Ni0.40Fe2O4 ferrite

An energy analysis of small-angle neutron scattering in the Zn_0.60Ni_0.40Fe₂O₄ ferrite nonirradiated and irradiated by fast neutrons has been performed. It has been revealed that the inelastic neutron scattering in the initial ferrite below T _C is due to not only the intradomain spin waves but also the significant contribution of the intraboundary long-wavelength magnetic excitations (w) and those localized near the domain boundaries (nw). The number of these magnetic excitations in the irradiated sample is significantly smaller. The elevated density of states of the w and nw magnetic excitations is assumed to be related to the competition between the intersublattice and intrasublattice exchange interactions, which is significantly weakened in the irradiated ferrite, where the corresponding exchange integrals are related by the inequality J _AB ? J _BB .