GL算法在FM振荡器的稳健性参数设计中的应用

针对FM振荡器幅度稳定性比较差的问题,运用GL算法,通过电路参数的合理搭配,减小了振荡管基极工作点的漂移,得出了比以往更好的稳定中心.     

非磁性掺杂下的铁磁/反铁磁系统中的交换偏置和矫顽场

采用Monte Carlo方法,分别讨论了在铁磁/反铁磁双层膜和铁磁/反铁磁单层混合膜中,掺入非磁性物质后,掺杂浓度对交换偏置以及矫顽场的影响.计算结果表明:随着掺杂浓度的增大,双层膜和单层膜交换偏置都有先增大后减小的现象,而其矫顽场则先减小后增大.在相同掺杂浓度下,对随机掺杂和规则掺杂两种不同掺杂方式的结果比较发现:铁磁/反铁磁双层膜中,规则掺杂下产生的交换偏置和矫顽场都得到了增强;对于单层混合膜,随机掺杂下的交换偏置更强,规则掺杂下的矫顽场更大.研究发现对于双层膜规则掺杂可明显地导致其磁滞回线的不对称性,说明铁磁/反铁磁系统中磁滞回线的不对称性与界面自旋微结构密切相关.     

连续可调谐OPO及其在Cs_2分子频率调制光谱中的应用

采用边带锁频技术 ,在II类相位匹配半整体光学参量振荡器 (OPO)中实现双谐振OPO稳定单频运转 ,通过调谐抽运光频实现OPO输出连续可调谐 ,最大连续调谐范围 2 .8GHz,将其应用于Cs2 分子的频率调制光谱 ,观测到室温附近Cs2 分子气室样品在 10 41.5 0 6nm附近的高分辨率光谱     

相分离Eu0.5Sr0.5MnO3体系中的场诱导磁相变及输运特性研究

研究了半掺杂相分离锰氧化物Eu_0.5Sr_0.5MnO₃样品的结构和电磁输运特性.在半掺杂情况下,该样品呈O′型正交结构,表明样品存在典型的Jahn-Teller畸变;在75 K附近样品的顺磁/反铁磁背景中开始出现铁磁相,在更低的温度42 K,4000 A/m磁场下M-T的场冷曲线和零场冷曲线出现明显分岔,样品的交流磁化率实部随温度的变化曲线中也在42 K观察到尖峰的出现,表现出团簇玻璃行为.在无外加磁场下该样品在 关键词： 多相竞争 半掺杂 铁磁团簇     

外应力场下铁磁/反铁磁双层膜系统中的自旋波

采用自由能极小的方法研究了铁磁/反铁磁双层膜系统在外应力场下的一致进动自旋波性质，即铁磁共振现象. 本模型中铁磁层很薄可看成单畴结构，但具有单轴磁晶各向异性和立方磁晶各向异性；而反铁磁层仅具有单轴磁晶各向异性，但其厚度趋于半无穷. 推导出了该系统的铁磁共振频率和频谱宽度的解析式. 结果表明，外应力场和界面交换耦合或反铁磁磁强度仅在弱磁场下对系统的铁磁共振有影响，且系统的铁磁共振行为按磁场强度可分为两支，其区分弱磁场和强磁场的临界场依赖于外应力场的方向. 另一方面，应力场方向的改变可借助于反铁磁层磁畴变化对铁磁层磁晶各向异性轴有影响. 关键词： 铁磁/反铁磁双层膜 界面耦合强度 铁磁共振 应力场     

Fe掺杂La0．8Sr0．2Co1-xFexO3磁性的研究

利用溶胶-凝胶法制备了一系列的La0.8Sr0.2Co1-xFexO3样品.通过研究在不同外加磁场下磁化强度和温度变化的关系发现,在较高的外场下La0.8Sr0.2Co1-xFexO3样品的磁性反转现象没有被观察到;在低场下La0.8Sr0.2Co1-xFexO3系统磁性反转现象被实现.这说明Fe的掺杂引起了La0.8Sr0.2Co1-xFexO3样品中铁磁和反铁磁之间的竞争,导致了La0.8Sr0.2Co1-xFexO3样品磁性反转;同时外加磁场的强弱影响了La0.8Sr0.2Co1-xFexO3系统磁性反转现象的发生,外加磁场增大使得在La0.8Sr0.2Co1-xFexO3样品中Co离子的自旋平行趋势更强,在铁磁和反铁磁之间的竞争中铁磁耦合占主导优势,因此在较高的外场下磁性反转现象没有被观察到.     

Tuning Exchange Anisotropy of Exchange-Biased System

Exchange anisotropy in FM/AFM bilayers has given a lot of static magnetization properties such as enhanced coercivity and magnetization loop shifts. These phenomena are primarily from the effective anisotropies introduced into a ferromagnet by exchange coupling with a strongly anisotropic antiferromagnet. These effective anisotropies can also be used to explain the dynamic consequences of exchange-biased bilayers. In this article, the dynamic consequences such as exchange-induced susceptibility, exchange-induced permeability, and the corresponding domain wall characteristics in the exchange-biased structures of ferromagnet/antiferromagnetl/antiferromagnet2 are studied. The results show that the second antiferromagnetic layer can largely affect the dynamic consequences of exchange-blazed bilayers. Especially in the case of critical temperature, the effects become more obvious. Practically, the exchange anisotropy of biased bilayer system can be tuned by exchange coupling with the second antiferromagnetic layer.     

Nonlinear Frequency-Modulation Distortion Analysis for VCO Based on Harmonic Balance Method

The analysis methods for the steady-state responses of the voltage tuning negative resistance oscillator (voltage-controlling oscillator, VCO) by the microwave nonlinear autonomous circuit harmonic balance method in millimeter-wave bands are studied in the paper. Firstly, the quasi-periodic characteristic of the steady-state response of the VCO modulated by a periodic signal is proved. Then, on the bases of the harmonic balance analysis and the inter-modulation balance analysis, a novel method for obtaining the steady-state tuning performance and the nonlinear frequency-modulation distortion characteristic of the VCO is presented. The total analysis process is aimed to a kind of NRD-guide Gunn diode VCO. The large-signal lumped equivalent circuit model of the millimeter-wave P⁺N-junction varactor is also given for explaining the algorithm and the principle of the NRD-guide VCO.     

基于调频信号子带相关性分析的回波特征提取方法

利用两种典型调频信号(LFM及HFM)的波形特点,本文提出了一种基于目标回波子带相关性的特征分析方法,并提取了回波统计特征。仿真与海上试验数据分析结果表明,该方法提取的回波统计特征对于识别水下人造金属目标与非目标具有较好的可分性。     

Exchange bias and magnetothermal properties in Fe@Mn nanocomposites

We have studied the Exchange Bias (EB) effect in nanocomposite films consisting of Fe nanoparticles (mean size ∼1.9 nm) embedded in an antiferromagnetic Mn matrix. They were produced by co-deposition through a gas aggregation cluster source and molecular beam epitaxy and have different Fe volume filling fractions (2.2% and 24.8%). The exchange field, higher in the sample with higher Fe concentration (at T=5 K, H_ex∼460 Oe for 24.8% and ∼310 Oe for 2.2% ), in both the samples decreases with increasing T, finally disappearing at T∼40 K. The EB properties have been studied in conjunction with results on the thermal dependence of the magnetic coercivity, zero-field-cooled and field-cooled magnetization and thermoremanence. The different Fe content strongly affects the magnetothermal properties, featuring superparamagnetic relaxation in the diluted sample and a reentrant ferromagnet-type transition in the concentrated one. Hence, the EB properties of the two samples have been discussed in consideration of such peculiarities of the magnetic behavior and highlighting the role of the Mn matrix.