Electric Resistance of Rare-Earth Metals and Their Alloys at High Temperatures: the Role of Magnetic Scattering

Physics of the Solid State - Results of an experimental study of the specific resistivity of rare-earth metals and their alloys are analyzed. A procedure to distinguish the contributions into the...     

Hyperfine Magnetic Anomaly in Atomic Spectra of Rare-Earth Elements

The constants of the hyperfine splitting in the atomic optical spectra of the rare-earth elements – Nd, Eu, Gd and Lu – were measured. The method of laser resonance fluorescence in the parallel atomic beam was used. The values of the hyperfine magnetic anomaly were determined from the comparision of magnetic dipole constant ratios of the neighbouring odd Z or N isotopes for the different atomic levels. The connection of these values and the parameters of atomic and nuclear structure is discussed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Magnetic Susceptibility of Nanocomposite Rare-Earth Titanates in Alternating Fields

Physics of the Solid State - The magnetic susceptibility of nanocomposite rare-earth titanates has been studied experimentally at low temperatures in the frequency range from 1 to 10 kHz. The...     

激光激励下镝离子掺杂氟硼酸盐玻璃荧光体的辐照参数

采用高温熔融法制备了镝离子掺杂氟硼酸盐玻璃荧光体,利用积分球绝对光谱测试系统,在453 nm蓝色激光二极管激发下,对玻璃荧光体的荧光光谱进行表征,解析出玻璃荧光体的相关绝对荧光参量。测试与计算结果表明,1.0 Wt% Dy₂O₃掺杂玻璃荧光体在功率15.81 mW的蓝色激光激发下,净发射光谱功率是286.91 μW,发射光子数为17.17×1014 cps,其荧光量子产率达到25.86%。为提高玻璃荧光体对泵浦激光的利用率,减少残余激光成分,进而改善组合光品质,制备了大体积的1.5 Wt% Dy₂O₃掺杂玻璃荧光体,在高功率的蓝色激光激发下获得白色照明效果,该玻璃荧光体在激发功率分别为56.0和252.7 mW的激光激发下,组合荧光对应的色坐标分别是(0.316, 0.287)和(0.303,0.268)。激光激励下的高效白色发光表明Dy3+掺杂氟硼酸盐玻璃荧光体在激光照明领域具有良好的应用前景。     

基于准经典近似研究强磁场中高温费米气体的统计性质

基于准经典近似研究强磁场中高温费米气体的统计性质,给出系统的统计特征量的解析式,分析磁场和温度对统计性质的影响.结果显示,与低温情况比较,高温下的统计特征量不再振荡,与自由费米气体比较,磁场总是降低系统的总能,增加系统的化学势、热容量、熵、压强和稳定性;而且温度越高,磁场对总能及热容量的影响越弱,对化学势的影响越大.     

Crystalline and Magnetic Enhancement of Nanocrystalline MnZn Ferrites Fabricated under a High Magnetic Field

Nanocrystalline Mn0.6Zn0.4Fe2O4 particles are synthesized under magnetic fields of O and 6 T, and their structural and magnetic properties are investigated. The magnetic field enhances the grain size and the lattice strain. Magnetic measurements show that the majority of the 6 T nanoparticles are superparamagnetic nearly from 40 to 300 K. It is interesting that the saturation magnetization of the 6 T sample is about 18% and 16% higher than that of the 0 T sample at 120 and 300K, respectively.     

Magnetic Relaxation in Nano-Phase Chromium Substituted Goethite

The magnetic and crystalline properties of chromium substituted goethite, -Fe_(1–x)Cr_(x)OOH (where x=0.00, 1.44, 3.00, 7.00, 10.14 wt.%) were studied using Mössbauer spectroscopy and X-ray diffraction. Transmission electron microscopy measurements showed that as the chromium concentration increased from 0 to 10.14 wt.%, the particle size decreased rapidly from 200 to 10 nm. X-ray diffraction analysis indicated that no lattice strain was present, even for chromium concentrations as high as 10.14 wt.%. Mössbauer spectra recorded at 300 K showed the presence of superparamagnetic relaxation in each sample. The relative area of the doublet component decreased, while that of the sextet component increased as the temperature decreased from 300 to 77 K. The mean hyperfine field measured at 77 K decreased from 49.6 T for the pure goethite to 44.9 T for the 10.14 wt.% chromium substitution. This decrease in the hyperfine field was attributed to both decreasing particle size and increasing chromium concentration.     

硼酸锂系列晶体的高压拉曼散射研究

本文进行了硼酸锂系列晶体的高压拉曼散射及其压致相变的研究。对于三硼酸锂（ＬｉＢ３Ｏ５），我们发现在５．０ＧＰａ有一可逆的晶态到晶态的相变，在２７．０ＧＰａ有一不可逆的晶态到非晶态的相变。二硼酸锂（Ｌｉ２Ｂ４Ｏ７）不可逆压致非晶相变发生在３２．０ＧＰａ附近。对于一硼酸锂，我们研究了０—５５．８ＧＰａ范围内的高压拉曼光谱，只在２．０ＧＰａ发现了一个晶态到晶态的相变，但未发现不可逆压致非晶化现象。在硼酸锂系列晶体中，不可逆压致非晶化的压力随Ｌｉ２Ｏ的含量的增加而升高。硼酸锂晶体中Ｌｉ２Ｏ的含量越高，压致非晶化越不容易发生，这与熔体急冷法制备硼酸锂玻璃的规律是一致的。     

Structural Transformations in Iron Borate under High-Temperature Annealing

Technical Physics - Scanning electron microscopy and X-ray diffractometry are used to study surface morphology and crystal structure of iron borate FeBO3 annealed at different temperatures....     

高场强核磁共振下测量水的自旋晶格弛豫时间

在反转恢复脉冲序列中增加双极性梯度场脉冲以压制辐射阻尼效应,从而使之能够在高场强核磁共振波谱仪(Bruker AV600)中较为准确测量水的自旋-晶格时间.这一方法应用于商品化成像对比剂Gd-DTPA的弛豫率测试,得到的结果和文献相似,证实了该方法的可靠性.进一步应用于新合成成像对比剂TEMDP-EMFs性能的评价.     

Magnetic Behavior of Nanocrystalline FeNbCrBCu Alloys at Elevated Temperatures

The magnetic behavior of nanocrystalline Fe_73.5Nb_4.5Cr₅B₁₆Cu₁ alloys is investigated in a series of specimens with different volume fractions of crystalline phase. It is shown that the Curie temperature of amorphous phase firstly decreases after structural relaxation in amorphous state and then rapidly increases during the first stages of crystallization. The strikingly different behavior of coercivity at elevated temperatures is observed for the samples with low and high volume fractions of nanocrystalline particles.     

高场水冷磁体上的高精度热电测量装置

拓扑材料是凝聚态物理近些年的一个重要研究领域.在对拓扑材料的研究中,利用较强的磁场可以观测到高度局域电子态中出现的新奇量子态与物理效应.热电效应是指受热材料中的载流子随着温度梯度由高温区往低温区移动时,所产生的电荷堆积的一种现象.热电效应是探究强磁场下拓扑材料反常物性的一种非常有效的手段.然而关于拓扑材料热电效应在强磁场下的研究较少,这主要是因为水冷磁体上缺乏热电效应的相关表征手段.本文针对水冷磁体在工作时机械振动很强且变场速率快的特点,改进了传统的热电测量装置,实现了在水冷磁体中32 T磁场下高精度的热电测量.通过对拓扑材料ZrTe₅和ZrSiSe的热电效应进行测量,验证了该装置的有效性.     

Exchange Interactions and Curie Temperatures in Dilute Magnetic Semiconductors

We discuss the origin of ferromagnetism in dilute magnetic semiconductors based on ab initio calculations for Mn-doped GaN, GaP, GaAs and GaSb. We use the Korringa–Kohn–Rostoker method in connection with the coherent potential approximation to describe the substitutional and moment disorder. Curie temperatures (T _C) are calculated from first-principles by using a mapping on a Heisenberg model in a mean field approximation. It is found that if impurity bands are formed in the gap, as it is the case for (Ga, Mn)N, double exchange dominates leading to a characteristic √c dependence of T _C as a function of the Mn concentration c. On the other hand, if the d-states are localized, as in (Ga, Mn)Sb, Zener's p–d exchange prevails resulting in a linear c-dependence of T _C. In order to have more precise estimations of T _C, effective exchange coupling constants J _ij 's are calculated by using the formula of Liechtenstein et al. It is found that the range of the exchange interaction in (Ga, Mn)N is very short. On the other hand, in (Ga, Mn)As the interaction is weaker but long ranged. Monte Carlo simulations show that the T _C values of (Ga, Mn)N are very low since percolation is difficult to achieve for small concentrations and the mean field approximation strongly overestimates T _C. Even in (Ga, Mn)As the percolation effect is still important.     

Identification of Single-Particle Configurations at Very High Spin in Some Rare-Earth Nuclei

The nuclear behaviour at high angular momenta is studied by γ-rays emitted in (HI, Xn) reaction. The study of very-high spin states in ¹⁵³Ho via discrete-line γ-ray spectroscopy and a comparison between the partial decay schemes of ¹⁵³Ho and the neighbouring ¹⁵²Dy and ¹⁵⁴Er nuclei are discussed in the context of the high spin structure. Second, we present comments on some phenomena observed at high spin states in ¹⁵³Ho and ¹⁵²Dy nuclei.     

Rational Design of Two-Dimensional Magnetic Chromium Borides Based on First-Principles Calculation

Two-dimensional(2D) magnetic materials have been experimentally recognized recently,however,the Curie temperatures(TC) of known 2D systems are quite low.Generally,magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements.Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high TC.Based on this,we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems.Using our self-developed software package IM2 ODE,we design a series of chromium-boride based 2D magnetic materials.Nine stable magnetic systems are identified.Among them,we find that CrB4-Ⅰ,CrB4-Ⅱ and CrBs-Ⅰ with common structural units [CrB8] are ferromagnetic metals with estimated TC of 270 K,120 K and 110 K,respectively.On the other hand,five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals.Additionally,we also find one antiferromagnetic semiconductor CrB2-Ⅰ.Our work may open new directions for identifying 2D magnetic systems with high TC.