低温熔盐中电沉积Sm-Co合金膜及其磁性能

在353 K的尿素-乙酰胺-NaBr-KBr熔体中, 用恒电位电解法在Cu基片上制备了Sm-Co合金膜. 利用循环伏安法研究了熔体的电化学行为. 电化学实验结果表明, 在Pt电极上, Co(II)+2e→Co(0)是一步完全的不可逆反应; 测得CoCl2-尿素-乙酰胺-NaBr-KBr熔体中, Co(II)在Pt电极上的传递系数α=0.31, 扩散系数D0=4.78×10^-5 cm2·s-1; Sm(III)难以单独沉积, 但能被Co(II)诱导共沉积, 在不同阴极电位下制备出不同Sm含量的非晶合金膜. 用等离子发射光谱仪(ICP)检测薄膜成分, 用SEM观察了薄膜的表面形貌结构, 用XRD和振动样品磁强计(VSM)分析样品退火前后的晶相和磁性能变化特征. 结果表明, 在923 K进行退火30 s后Sm-Co薄膜由非晶转变为多晶结构, 并以hcp晶相结构为主; 退火和Sm含量对Sm-Co合金膜的磁性能有重要的影响.     

二维异质结光子晶体中含近邻点缺陷的弯曲波导的可调谐滤波特性

应用时域有限差分(FDTD)法,对光在二维异质结光子晶体中含两个近邻点缺陷直角弯曲波导的传输特性进行了数值模拟研究。计算结果表明,具有特定本征共振频率的光子晶体微腔(点缺陷),可将在其邻近波导中传播的相同频率成分的光波"引入"到微腔中。"引入"的频率依赖于异质结光子晶体弯曲波导和微腔的参量,从而能够实现调变"引入"频率。通过改变点缺陷周围介质材料(液晶)的折射率或相关介质柱半径,可分别实现约31 nm或12 nm的波长调谐范围。计算结果为光通信中的调谐、上/下载滤波器,提供了一条新的设计思路和依据。     

非晶态TM—Zr合金的磁性

本文详细地介绍了这类非晶态合金在磁性质、临界行为、自旋波激发、混磁性及吸氢对磁结构影响等方面的研究进展．     

Effect of oxygen vacancy defect on the magnetic properties of Co-doped ZnO

The influence of oxygen vacancy on the magnetism of Co-doped ZnO has been investigated by the first-principles calculations.It is suggested that oxygen vacancy and its location play crucial roles on the magnetic properties of Co-doped ZnO.The exchange coupling mechanism should account for the magnetism in Co-doped ZnO with oxygen vacancy and the oxygen vacancy is likely to be close to the Co atom.The oxygen vacancy (doping electrons) might be available for carrier mediation but is localized with a certain length and can strengthen the ferromagnetic exchange interaction between Co atoms.     

第一性原理研究氧在Ni(111)表面上的吸附能及功函数

采用基于密度泛函理论（DFT）广义梯度近似（GGA）下的第一性原理方法系统地研究了不同覆盖度下O在Ni（111）表面的吸附特性.计算结果表明,O在Ni（111）表面的稳定吸附位为三重面心立方（fcc）洞位,吸附能随着覆盖度的增加而减小,O诱导Ni（111）表面功函数的变化量与覆盖度成近线性关系,并随着覆盖度的增加而增大.同时,通过对电子密度和分波态密度的分析发现：O在Ni（111）表面的吸附使得Ni表面电子向O原子转移,形成表面偶极矩,导致功函数增加;表面Ni原子的3d轨道和O的2p轨道通过耦合、杂化作用形成成键态和反键态,而反键态几乎不被占据,因而O—Ni键相互作用比较强,吸附能较大. 关键词： 表面吸附 密度泛函理论 吸附能 功函数     

水印的最佳置乱度置乱算法

介绍了数字图像置乱的基本概念,引入置乱度的定义对置乱后的图像作定量分析,提出了基于二维混沌映射Arnold变换的数字图像置乱方法,通过分析Arnold变换的周期及控制参数,实现对数字图像的最佳置乱。并通过对数字水印信号进行置乱,使得原始水印信号的相关性减弱,在遭到剪切攻击时,可以将提取出的水印信号的错误码元尽可能地分散开来,因此有效地提高了数字水印算法的抗剪切攻击性能。     

Monte carlo simulation of magnetization and coercivity of free magnetic clusters

Based on Monte Carlo method, the oscillatory behaviour of the average magnetic moment as a function of the cluster sizes and the temperature dependences of magnetic moment with different sizes have been studied. It is found that the oscillations superimposed on the decreasing moment are associated with not only the geometrical structure effects but also the thermal fluctuation. The hystereses and thermal coercivities for free clusters with zero and finite uniaxial anisotropies have been calculated. The simulated thermal dependence of the coercivity is consistent with the experimental result, but does not fit the T^α law in the whole temperature range. It is evident that an easy magnetization direction and an anisotropy resulting from the spin configurations exist in the free clusters with the pure exchange interaction, which is also proved by the natural angle and energy distribution of clusters. A systematic theoretical analysis is also made to establish the relationship between natural angle and coercivity.     

Enhanced Magnetoresistance of （La0.67Ca0.33MnO3） Composites Coated by Zn0.95Co0.05O

La0.7Ca0.3MnO3：xZn0.95Co0.05O （x=0.0,0.05, 0.1, 0.15mol） composites are prepared by a sol-gel process. X- ray diffraction and energy diffraction spectroscopy reveal that there is no evidence of a reaction between the La0.7 Ca0.3 MnO3 （LCMO） and Zn0.95Co0.05 O （ZCO）. Magnetization M, Curie temperature Tc and metal-insulator transition temperatures Tp are observed to decrease with increasing ZCO content. Compared with x = 0.0, a great enhancement in the magnetoresistance （MR） is observed at around Tc for x = 0.05, 0.10, 0.15. Based on the tunneling MR and percolation models, this great change of MR is well explained.     

本征磁性拓扑绝缘体MnBi2Te4电子结构的压力应变调控

由于MnBi2Te4电子结构具有对晶格常数的改变相当敏感的特性,本文采用基于密度泛函理论的第一性原理方法对MnBi2Te4反铁磁块体的电子结构施加等体积应变调控.研究发现体系能带结构在材料等体积拉伸和压缩作用下变化灵敏,体系出现绝缘体-金属相变.特别地,当施加特定应变后导带和价带在Γ处出现交叉,体系呈零带隙状态.在此应...     

铬掺杂氧化锌薄膜的超声喷雾法制备及其光学与磁学性质

用注射超声喷雾法将前驱体由针管直接送入超声喷头内,在石英基板上制备Zn_(1-x)Cr_xO(x=0.0,0.01,0.03,0.05)薄膜。采用X射线衍射仪、扫描电子显微镜、荧光光谱仪、紫外-可见分光光度计、振动样品磁强计(VSM)等对薄膜的结构、光学和磁学性质进行测量。实验结果表明,未掺杂的ZnO薄膜为六角纤锌矿结构,沿着c轴(002)择优取向,而Cr掺杂抑制了薄膜的c轴择优取向性;掺杂后的薄膜平均晶粒尺寸均增大,且当x=3%时,晶粒尺寸最大,达31.4nm。扫描电镜(SEM)下薄膜呈球形颗粒状,并且在x=5%下,薄膜出现了长条状的微观形貌。Cr掺杂使样品的光致发光谱(PL)发生了很大的变化:未掺杂的样品的PL谱在378nm处存在一个紫外发射峰,对应于550nm附近还存在一个由于缺陷态引起的绿光发射峰;掺Cr样品只有在350~550nm的很宽的范围内存在一个发射峰,对其进行高斯拟合后,发现掺Cr量为x=1%,3%,5%下样品均存在V_(Zn)(锌空位)、Zn_i(Zn间隙位)、V_(Zn)~-(带一个电子的锌空位)内部缺陷态,且当x=3%时,V_(Zn)最多。Cr的掺杂使得薄膜的带隙增大,并且x=3%时,禁带宽度最大,达到3.374eV。掺Cr的三个样品均具有室温铁磁性,且x=3%样品的磁化强度最大,其与V_(Zn)(锌空位)最大相对应,验证了Cr~(3+)和V_(Zn)的缺陷复合体是ZnO∶Cr样品具有稳定的铁磁有序的最有利条件的理论预测。