粉末倍频系数的模拟研究

根据Kurtz粉末倍频理论,使用光纤光谱仪自行设计搭建一个粉末倍频测试系统,该系统可在基频光波入射方向不变的情况下,通过转动旋转臂在不同方向探测二次谐波,并且具有较高的精确度和灵敏度。使具有位相匹配特性的颗粒尺寸范围扩大为46μm～250μm 。使用波长为1.064μm的基频光,对KIO3晶体粉末的倍频效应进行了测试。测试结果表明,KIO3晶体粉末透射倍频光具有位相匹配特性。这一测试结果与已报道结果相一致。通过数值模拟实验测试曲线,获得了KIO3晶体粉末的倍频系数d2ω的值为9.7×10-12m/V。这一模拟值与已报道的KIO3晶体对该基频光波产生的倍频系数d32的值相吻合。由此可见,该方法切实可行。并且可推广应用到其他晶体材料的非线性特性测试研究。     

An electron spin resonance study of Eu doping effect in La_(4/3)Sr_(5/3)Mn_2O_7 single crystal

The effect of Eu3+ion doping in the La sites of single-crystal La4/3Sr5/3Mn2O7was investigated. Electron spin resonance(ESR) was applied to La4/3Sr5/3Mn2O7and(La0.8Eu0.2)4/3Sr5/3Mn2O7single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance(PMR)and anisotropic ferromagnetic resonance(FMR) lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic(PM) phase and the ferromagnetic(FM) phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal(La0.8Eu0.2)4/3Sr5/3Mn2O7below the temperature of spin freezing Tf(～ 29.5 K).     

Magnetic transition behavior of perovskite manganites Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 polycrystalline

A polycrystalline sample Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction(XRD) patterns, a superconducting quantum interference device(SQUID), and electron spin resonance(ESR). The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Nd_(0.5)Sr_(0.3)Ca_(0.2)MnO_3 undergoes three magnetic transitions: ferromagnetic transition at TC≈ 210 K, charge-ordering at TCO≈ 175 K, and antiferromagnetic transition at TN= 155 K. In addition, the activation energy Ea ≈ 52.78 me V can be extracted by curve fitting.     

VoIP终端存储系统设计

介绍了VoIP终端SoC的架构,采用片内存储器、存储器控制器、SSRAM、SDRAM及FLASH组成VoIP终端硬件平台的存储系统.分析了两种存储器控制器方案的优缺点.提出一种采用集成方式的存储器控制器结构.利用Verilog HDL设计了该存储器控制器IP,并给出访问SDRAM的仿真结果.存储系统已成功应用于VoIP SoC项目中.     

Evidence of phase separation in Nd1-xSrxMnO3 （x=0.50, 0.51, 0.52, 0.53, 0.54, 0.55）

The temperature dependence of Mn ion magnetization and the conductivity difference versus temperature provide phase separation evidence in Nd1-xSrxMnO3 (x=0.50, 0.51, 0.52, 0.53, 0.54, 0.55). This is different from other reports and may suggest that a fully charge-ordered state exists in quite a narrow range; the sample preparation procedure affects the charge ordering. The polaron effect also plays an important role in explaining the conductivity.     

Spontaneous magnetization and resistivity jumps in bilayered manganite （La0.8Eu0.2）4/3Sr5/3Mn2O7 single crystals

Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into Laa/3Sr5/3Mn2O7, from the resulting single crystal （La0.8Eu0.2）a/3Sr5/3Mn2O7 we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For （Lao.sEuo.2）a/3Sr5/3Mn2O7, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of Laa/3Sr5/3Mn2O7 and cause such interesting behaviours.     

Electron spin resonance study of the Ba-doping manganite Nd0.5Sr0.5MnO3

We have performed magnetization measurements and electron spin resonance （ESR） on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 （x = 0.1）. Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K （～ Tc） and 185 K （～ TN）, the system coexists of the paramagnetic phase and the ferromagnetic （FM） phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic （AFM） phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2＋ ions for the smaller Sr^2＋ ions.     

双层钙钛矿(La_(1-x)Gd_x)_(4/3)Sr_(5/3)Mn_2O_7(x=0,0.05)的相分离

采用传统固相反应法制备(La1-xGdx)4/3Sr5/3Mn2O7(x=0,0.05)多晶样品,并通过测量样品的磁化强度与温度的变化曲线(M-T曲线)、电子自旋共振谱(ESR谱)和电阻率与温度的变化曲线(ρ-T曲线),研究了x=0和x=0.05样品的相分离现象.研究结果表明,两样品在低温部分出现了反铁磁与铁磁相互竞争的现象,体现出团簇自旋玻璃态的特征.x=0和x=0.05样品分别在125—375 K和100—375 K范围内观察到类Griffiths相,同时发现掺杂使得三维铁磁有序温度(T3Dc0≈125 K和T3Dc1≈100 K)降低,而对类Griffiths温度(TG≈375 K)没有明显影响.在TG温度以上两样品均表现出纯顺磁特性.其电特性表明,x=0样品在整个测量范围内出现两次绝缘-金属转变,这是由钙钛矿锰氧化物共生现象所致.而x=0.05样品只出现一次绝缘-金属转变,表明掺杂能抑制共生现象的产生.通过对ρ-T曲线的拟合发现两样品在高温部分的导电方式基本都遵循三维变程跳跃的导电方式.     

钙钛矿型锰氧化物(La$lt;sub$gt;0.8$lt;/sub$gt;Eu$lt;sub$gt;0.2$lt;/sub$gt;)$lt;sub$gt;4/3$lt;/sub$gt;Sr$lt;sub$gt;5/3$lt;/sub$gt;Mn$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;7$lt;/sub$gt;的磁性和电性研究

采用传统固相反应法制备钙钛矿型锰氧化物 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇多晶样品, X-射线衍射分析表明, 样品(La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇结构呈现良好的单相. 通过磁化强度随温度的变化曲线(M-T)、不同温度下磁化强度随磁场的变化曲线(M-H)和电子自旋共振谱发现: 在300 K以下, 随着温度的降低, 样品先后经历了二维短程铁磁有序转变 (T_C^2D ≈ 282 K)、三维长程铁磁有序转变(T_C^3D ≈ 259 K)、奈尔转变(T_N ≈ 208K)和电荷有序转变(T_CO ≈ 35 K); 样品 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇在T_N以下, 主要处于反铁磁态; 在T_C^3D达到370 K时, 样品处于铁磁-顺磁共存态, 在370 K以上时样品进入顺磁态. 此外, 分析电阻率随温度的变化曲线(ρ-T)得到: 样品在金属-绝缘转变温度(T_P ≈ 80 K)附近出现最大磁电阻值, 其位置远离T_C^3D, 表现出非本征磁电阻现象, 其磁电阻值约为61%. 在T_CO以下, 电阻率出现明显增长, 这是由于温度下降使原本在高温部分巡游的e_g电子开始自发局域化增强所致. 通过对 (La_0.8Eu_0.2)_4/3Sr_5/3Mn₂O₇的ρ-T 曲线拟合, 发现样品在高温部分的导电方式基本遵循小极化子的导电方式. 关键词： 磁性 电性 金属-绝缘转变温度 电子自旋共振     

ICP-AES法测定润滑油元素含量的前处理方法

准确测定润滑油中元素的含量对于监控润滑油使用性能和预测各种润滑机械故障具有重要的意义。介绍了高温灰化、溶剂稀释、湿法消解、乳化、压力融弹、微波消解6种前处理方法在ICP-AES测定润滑油元素含量中的应用。