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本文通过传统的固相反应法制备了R型六角铁氧体BaFe4-xTi2+xO11 (x= 0, 0.25, 0.5, 0.75, 1), 并且对它的原子价态以及磁性行为进行了研究. X 射线光电子能谱(XPS)结果显示了随着掺杂含量的增加, 体系中Fe3+离子逐渐减少而Fe2+离子逐渐增加. 由于具有非对称结构的阻挫晶格中存在各种关联作用的竞争, 使得BaFe4-xTi2+xO11体系表现出了复杂的磁有序行为, 在T1~250 K和T2~83 K两处存在磁转变. 对这一系列掺杂样品, 在相变温度T1之上表现顺磁行为, 而在相变温度T2前后的磁化强度都表现出低场下随磁场的增加快速增加, 高场下则线性变化且在5×104 Oe时还未达到饱和的行为, 表明这一系列掺杂样品是典型的倾斜反铁磁态(canted antiferromagnetic) 或者亚铁磁态. 相似文献
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We present the temperature-dependent susceptibility and specific heat measurement of spinel ZnV_2O_4.The structural transition with orbital ordering and the antiferromagnetic transition with spin ordering were observed at 50 K and 37 K,respectively.By analysis of the hysteresis behavior between the specific heat curves obtained in warming and cooling processes,the structural transition was confirmed to be the first-order transition,while the antiferromagnetic transition was found to be of the second-order type.At the structural transition,the latent heat and entropy change were calculated from the excess specific heat,and the derivative of pressure with respect to temperature was obtained using the Clausius-Clapayron equation.At the magnetic transition,the width of the critical fluctuation region was obtained to be about 0.5 K by comparing with Gaussian fluctuations.In the critical region,the critical behavior was analyzed by using renormalization-group theory.The critical amplitude ratio A~+/A~- = 1.46,which deviates from the 3D Heisenburg model;while the critical exponent α is-0.011,which is close to the 3D XY model.We proposed that these abnormal critical behaviors can be attributed to strong spin-orbital coupling accompanied with the antiferromagnetic transition.Moreover,in the low temperature range(2-5 K),the Fermi energy,the density of states near the Fermi surface,and the low limit of Debye temperature were estimated to be2.42 eV,2.48 eV~(-1),and 240 K,respectively. 相似文献
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弹性或弹塑性土体中桩基的大变形分析 总被引:1,自引:0,他引:1
采用弧坐标,首先建立了位于弹性地基或弹塑性地基上并具有初始位移的桩基大变形行为的非线性微分方程组,并采用Winkeler模型来模拟地基对桩基的抗力;其次,应用微分求积方法离散非线性微分方程组,得到一组离散化的非线性代数方程,并给出了利用Newn-Raphson方法求解非线性代数方程的步骤;作为应用给出了数值算例,得到了桩顶受组合载荷作用时,变形后桩基的构形、弯矩和剪力,考察了土的弹性和弹塑性性质、桩基初始位移、荷载等参数对桩基力学行为的影响.最后将模型进行简化,得到了小变形理论的解析解,并比较了由大变形理论与小变形理论所得结果的差别. 相似文献
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粘弹性矩形板的稳定性分析 总被引:11,自引:0,他引:11
根据动力系统的观点研究了四边简支粘弹性矩形板的稳定性,利用Laplace变换得到了蠕变临界载荷λcr和瞬时临界载荷λcs。同时采用Laplace变换和Galrkin方法计算了时间相关载荷λ(t)的峰值λ满足条件λer〈λ〈λcs时,线性和非线性问题的挠度随时间的变化规律。 相似文献
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Based on the assumption of finite deformation, the Hamilton variational principle is extended to a nonlinear elastic Euler-type beam-column structure located on a nonlinear elastic foundation. The corresponding three-dimensional (3D) mathematical model for anaiyzing the nonlinear mechanical behaviors of structures is established, in which the effects of the rotation inertia and the nonlinearity of material and geometry are considered. As an application, the nonlinear stability and the post-buckling for a linear elastic beam with the equal cross-section located on an elastic foundation are analyzed.One end of the beam is fully fixed, and the other end is partially fixed and subjected to an axial force. A new numerical technique is proposed to calculate the trivial solution,bifurcation points, and bifurcation solutions by the shooting method and the Newton-Raphson iterative method. The first and second bifurcation points and the corresponding bifurcation solutions are calculated successfully. The effects of the foundation resistances and the inertia moments on the bifurcation points are considered. 相似文献
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Electron Transport Behavior of Multiferroic Perovskite BiMnO_3 Prepared by Co-Precipitation Method 下载免费PDF全文
Perovskite BiMnO_3 samples are successfully synthesized by the co-precipitation method at relatively low pressure and moderate temperature.The temperature dependences of resistivity are measured and systematically investigated.It is shown that the electrical resistivity increases sharply with the decrease of temperature above 210 K and the fitted results demonstrate that the thermally activated conduction model is the dominant conduction mechanism for the electron transport behaviors in this temperature region.A dual conducting mechanism,i.e.,the variable range hopping and thermal activated conduction,is suggested to be responsible for the transport behaviors of BiMnO_3 in the region of 180–200 K.Moreover,the resistivity increases slightly with the decrease of temperature below 180 K and the transport is governed by the variable range hopping mechanism. 相似文献