溶剂热合成法制备的Zn1-xMnxO和Zn1-2xMnxLixO纳米材料的磁学性质

用溶剂热合成法在160oC制备出Zn_1-xMn_xO纳米棒和Zn_1-2xMn_xLi_xO纳米颗粒. XRD和拉曼测试结果表明Mn离子已很好地掺入ZnO母体中. M-H图中未观察到磁回滞,ESR谱中的精细结构说明掺杂的Mn离子间没有铁磁相互作用. 共掺Li仅仅改变了产物的形貌,并不能改变其磁学性质.     

针状纳米MnxNi0.5-xZn0.5Fe2O4的共沉淀法制备及表征

通过在碱液中共沉淀Mn²⁺、Ni²⁺和Fe²⁺后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了Mn_xNi_0:5-xZn_0:5Fe₂O₄棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,Mn_xNi_0:5-xZn_0:5Fe₂O₄样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7～8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe.     

LiFexMn1-xPO4固溶体的密度泛函理论与电化学研究

本文用DFT计算方法研究了LiFe_xMn_1-xPO₄的热力学稳定性和嵌/脱锂电位. 结果表明,LiFe_xMn_1-xPO₄固溶体的自由能比相分离的LiFePO₄/LiMnPO₄混合物略高,这两种形式可能在实际LiFe_xMn_1-xPO₄材料中共存. 计算表明,LiFe_xMn_1-xPO₄固溶体的嵌/脱锂电位随锰/铁比以及过渡金属离子的空间排列而变化,并用计算结果解释了放电曲线的形状. 采用固相反应法合成了LiFe_xMn_1-xPO₄材料并研究了其电化学性质,实验中观察到附加的放电平台,其出现可能与LiFe_xMn_1-xPO₄固溶体的存在有关.     

Al3+掺杂的CuZn铁氧体的结构，电学和磁学特性

采用固相合成反应技术制备纳米Cu_0.5Zn_0.5Fe_2-xAl_xO₂(x=0.0,0.1,0.2,0.3,0.4和0.5)铁氧体材料,研究Al³⁺含量对结构,电学和磁学性质的影响. 采用X射线衍射研究单相立方尖晶石结构. 利用Scherrer公式估算晶粒尺寸. 测定了温度依赖的直流电阻率.结果表明随Al³⁺含量的增加,晶格常数减小,孔隙度增加,饱和磁化强度值降低,Al³⁺对铁氧体的介电常数、介电损耗角的正切值和介质损耗因子等介电性能有明显影响,这可能与空间电荷极化有关.     

Co1-xMnx合金电子结构和磁性的理论研究

Co_1-xMn_x合金的磁性强烈地依赖于其结构以及Mn的相对含量.从第一性原理出发,用线性缀加平面波(LAPW)方法,分别计算了x=0.00,0.25,0.50,0.75,1.00的情况下,面心立方(fcc)和体心立方(bcc)结构的Co_1-xMn_x合金的电子结构和基态磁性.随x的增大,fcc结构的Co_1-xMn_x合金的磁性从铁磁性和亚铁磁性变为反铁磁性;bcc结构Co相似文献   

Mg2+掺杂Zn2SiO4:Mn2+的溶胶-凝胶法合成及真空紫外发光特性研究

采用溶胶-凝胶法（sol-gel method）于不同气氛条件下成功合成了Zn_1.92-xMg_xSiO₄:0.08Mn²⁺（0≤x≤0.12）系列粉末样品.利用X射线衍射(XRD)、光致发光(PL)谱等分析手段对Zn_1.92-xMg_xSiO₄:0.08Mn²⁺系列     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Al高掺杂浓度对ZnO禁带和吸收光谱影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法, 建立了未掺杂与不同浓度的Al原子取代Zn原子的两种Zn_1-xAl_xO超胞模型,分别对模型进行了几何结构优化、态密度分布和能带分布的计算. 结果表明: ZnO高掺杂Al的条件下, 掺杂的Al原子浓度越大,间隙带越窄, 蓝移越弱. 计算结果和实验结果相一致.     

室温下Ga1-xHoxN (x=0.0 and 0.05)稀磁半导体薄膜磁性

采用热蒸镀技术和后续氨退火制备了Ho掺杂GaN稀磁半导体薄膜. X射线衍射分析表明,所有的峰属于六角纤锌矿结构. 利用扫描电子显微镜和能量色散谱分别进行了表面形貌和成分分析. 用振动样品磁强计在室温测定了Ga_1-xHo_xN(x=0.0,0.05)的室温铁磁性. 磁性测量结果表明,未掺杂薄膜GaN具有抗磁性行为,而Ho掺杂Ga_0.95Ho_0.05N的薄膜表现出铁磁行为.     

非简并p型Hg1-xMnxTe单晶(x>0.17)的负磁电阻机理研究

研究磁性半导体中负磁电阻产生机理对正确理解载流子与磁性离子间的sp-d磁交换作用 是非常重要的.通过变温(10---300 K)磁输运和变温(5---300 K)磁化率实验研究了一系列不同Mn含量 非简并p型Hg_1-xMn_xTe单晶(x>0.17)的负磁电阻和顺磁增强效应. 实验结果表明其负磁电阻与温度的关系和磁化率与温度的关系基本一致, 两者都包含一个呈指数型变化的温度函数exp(-K/T).根据磁性半导体的杂质能级理论, 非简并p型Hg_1-xMn_xTe单晶在低磁场范围内出现负磁电阻效应的主要物理机理 为外磁场的磁化效应使得受主杂质或受主型束缚磁极化子的有效电离能减小.     

Structural,magnetic and151Eu Mössbauer studies on EuTCu4 (T-Al,Pd and Ag) compounds

New ternary compounds having the formula EuTCu₄ where T=Al, Pd and Ag have been synthesized. All these compounds are found to crystallize in the hexagonal CaCu₅ type structure. Magnetization measurements reveal that these compounds are magnetically ordered with magnetic moments close to 7 μ_B. The Curie temperatures obtained from low field ac susceptibility measurements are 26K, 25K and 50K for T-Al, Pd and Ag respectively.¹⁵¹Eu Mössbauer studies at room temperature show a large negative isomer shift relative to SmF₃. A hyperfine split pattern is observed at 4.2K in all these compounds, indicating that Eu ion is present in a divalent state and is magnetically ordered.     

Dielectric relaxation and ac conduction in multiferroic TbMnO3 ceramics: Impedance spectroscopy analysis

Polycrystalline samples of Tb_1−xAl_xMnO₃ (x = 0, 0.1, 0.2) have been synthesized by means of standard high-temperature solid-state reaction technique. Detailed studies on the effect of compositional variation of aluminum (Al) on the electrical behavior (complex impedance Z*, complex modulus M*, and relaxation mechanisms) of the parent TbMnO₃ have been performed by using the nondestructive complex impedance spectroscopy technique at temperatures above room temperature. In the temperature range covered, the impedance plots signalize that the grains are the unique responsible for the conduction mechanism of the concerned material. The impedance spectra are well modeled in terms of electrical equivalent circuit with a grain resistance (R_g) and constant phase element impedance (Z_CPE). The conductivity data of the undoped and Al-doped samples are well fitted by the universal Jonscher's power law. The resulting fitting parameters indicate that for the studied samples, the hopping process occurs between neighboring sites. Activation energy values for dc conductivity are calculated for undoped and Al-doped samples and found to decrease when Al is incorporated. In turn, the emergence of single arc in the complex modulus spectrum for all the compositions of Al suggests that for the studied samples only one type of relaxation behavior is present at the selected temperatures. A non-Debye-type relaxation is clearly verified. The relaxation process in the present samples seems to be composition and temperature dependent, particularly at higher frequencies.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

脉冲磁场下水热法制备Cr掺杂ZnO稀磁 半导体晶体

本文以ZnCl₂, CrCl₃. 6H₂O和氨水缓冲溶液为原料, 在4T脉冲磁场下水热法制备了Cr掺杂ZnO稀磁半导体晶体, 通过X射线衍射分析、扫描电子显微镜观察及采用振动样品磁强计进行磁性分析等, 探讨了脉冲磁场对其微观结构及磁性能的影响. 结果表明: Cr掺杂ZnO稀磁半导体晶体仍保持ZnO的六方纤锌矿结构, 脉冲磁场具有促进晶粒生长及取向排列的作用, 4T脉冲磁场条件下合成的Cr掺杂ZnO稀磁半导体具有良好的室温铁磁性, 其饱和磁化强度(M_s)为0.068 emu/g, 而无脉冲磁场情况下制备的样品室温下呈顺磁性, 并且, 脉冲磁场下制备将稀磁半导体的居里温度提高了16 K.     

Study of Sm-doped ZnO samples sintered in a nitrogen atmosphere and deposited on n-Si(1 0 0) by evaporation technique

The samarium doping zinc oxide (Zn_1-xSm_xO) with (x=0.0, 0.04, 0.05 and 0.17) polycrystalline thin films have been deposited on n-Si(1 0 0) substrate using thermal evaporation technique. Ceramic targets for deposition were prepared by the standard solid-state reaction method and sintered in nitrogen atmospheres. X-ray diffraction and scanning electron microscopy analyses show that the bulk and films features reveal wurtzite crystal structure with a preferential (1 0 1) crystallographic orientation and grows as hexagonal shape grains. According to the results of the Hall effect measurements, all the films show p-type conductivity, possibly a result of nitrogen incorporation into the Sm-doped ZnO samples. Magnetic measurements show that ferromagnetic behavior depends on the Sm³⁺ concentration. For a film with lower Sm₂O₃ contents (x=0.04), a phenomenon of paramagnetism has been observed. While, with further increase of Sm³⁺ contents (x=0.05) the ferromagnetic behavior has been observed at room temperature. However, at higher doping content of Sm³⁺, the ferromagnetic behavior was suppressed. The decrease of ferromagnetism with increasing doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Zn_1-xSm_xO films.     

Synthesis and magnetic properties of NiFe2−xAlxO4 nanoparticles

Nanocrystalline Al-doped nickel ferrite powders have been synthesized by sol–gel auto-ignition method and the effect of non-magnetic aluminum content on the structural and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain sizes from XRD data have been verified using transmission electron microscopy (TEM). TEM photographs show that the powders consist of nanometer-sized grains. It was observed that the characteristic grain size decreases from 29 to 6 nm as the non-magnetic Al content increases, which was attributed to the influence of non-magnetic Al concentration on the grain size. Magnetic hysteresis loops were measured at room temperature with a maximum applied magnetic field of ≈1 T. As aluminum content increases, the measured magnetic hysteresis curves become more and more narrow and the saturation magnetization and remanent magnetization both decreased. The reduction of magnetization compared to bulk is a consequence of spin non-collinearity. Further reduction of magnetization with increase of aluminum content is caused by non-magnetic Al³⁺ ions and weakened interaction between sublattices. This, as well as the decrease in hysteresis was understood in terms of the decrease in particle size.     

Magnetic phase diagram of double-layered La2−2xCa1+2xMn2O7 manganite

Double-layered manganite La_2−2xCa_1+2xMn₂O₇ have been synthesized for compositions ‘x’=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 by solid state reaction method. From X-ray diffraction study, their crystal structures were found to be tetragonal perovskite with lattice parameters decreasing with increasing ‘x’. The decreasing lattice parameters affect the balance between in-plane, intra-bilayer and inter-bilayer exchange interactions, which is reflected on magnetotransport properties. The metal-to-insulator transition temperature is found to vary with composition and peaked around ‘x’=0.3. From ac-susceptibility study, 2D-ferromagnetic ordering was observed at higher temperatures for all compositions whereas 3D-ferromagnetic ordering was observed at quite low temperatures. In low-temperature region, decreasing susceptibility shows antiferromagnetic state for all compositions. On the basis of electrical and magnetic properties, a magnetic phase diagram is given.     

Magnetic susceptibility of single-crystal hexagonal nickel sulphide

The magnetic susceptibilities of five single-crystals of hexagonal NiS, with compositions ranging from NiS-NiS_1.02 have been measured in the temperature range 78–300°K. The susceptibility curves have a markedly different shape from that normally predicted for an antiferromagnet. This results from the first-order character of the phase transition at T_N.     

Microstructural and magnetic properties of Pr–BiCo co-substituted M-type Sr–Ca hexaferrites

We have synthesized the Pr–BiCo substituted hexaferrites with compositions of Sr_0.8-xCa_0.2Pr_xFe_12.0-x(Bi_0.5Co_0.5)_xO₁₉ (0.0?≤?x?≤?0.5) by the standard ceramic method. Results of X-ray diffraction analysis exhibits that the synthesized hexaferrites with x from 0.0 to 0.3 are in single magetoplumbite structure, and impurity phases are observed when x?≥?0.4. The surface morphology of magnets shows that hexaferrite grains have a hexagonal platelet shape with clear grain boundaries. The remanence first increases with x from 0.0 to 0.1, and then decreases when x?≥?0.1. The intrinsic coercivity decreases with x from 0.0 to 0.1, and then increases when x?≥?0.1. With x from 0.0 to 0.4, the changing trend of magnetic induction coercivity is in agreement with that of H_cj, while at x?≥?0.4, H_cb decreases. The maximum energy product initially increases with x from 0.0 to 0.2, and then decreases when x?≥?0.2.