(Ga, Gd, As) film growth on GaAs substrate by low-energy ion-beam deposit

(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

以1-苯基-3-甲基-4-苯甲酰基代吡唑酮[5]萃取稀土和钍铀钛锆及其在分析化学中的某些应用

本文研究了以PMBP-苯萃取稀土和钍、铀、钛、锆的萃取行为。测定了La、Ce、Pr、Nd、Sm、Gd、Dy、Yb、Y、U(Ⅵ)、Ti、Th和Zr的pH_(1/2)值,计算了它们的萃取平衡常数。并介绍了近十年来作者将此萃取剂应用于铀、钍、稀土、鋰、钢铁合金及岩石中痕量稀土、钍和钙的分离和测定方面的工作。实践证明,PMOP合成简便、价格低廉、萃取能力较强,是比TTA更为优越的萃取剂。

离子束外延制备GaAs:Gd薄膜

　室温条件下,用低能离子束外延制备了GaAs∶Gd薄膜,X射线衍射(XRD)结果表明除了GaAs衬底峰没有发现其它新相的衍射峰,并借助于高分辨X射线衍射(HR XRD)进一步分析了晶格常数的变化特点。俄歇电子能谱(AES)分析了样品表面的成分,及元素随深度的分布规律,在60nm深处元素的相对含量发生明显改变,运用原子力显微镜(AFM)揭示了样品表面的形貌特点。

Superconductivity, spin-glass properties, and ferromagnetism in amorphous La-Gd-Au alloys

The superconducting and magnetic properties of splat cooled amorphous alloys of composition (La_100-xGd_x)₈₀Au₂₀ (0 ≤ x ≤ 100) have been studied. The La₈₀Au₂₀ alloys are ideal type II super-conductors (critical temperature T_c = 3.5° K ). The concentration range (x less than 1) where superconductivity and spin-glass freezing n1ight coexist has been studied in detail. The spin-glass alloys (0 less than x less than 70) exhibit susceptibility maxima and thermomagnetic history effects. In the absence of complications due to crystal field and enhanced matrix effects, a phenomenological model is proposed in which the magnetic clusters are treated as single spin entities interacting via random forces using the molecular field approach. The fundamental parameters (such as the strength of the forces and the size of clusters) can be deduced from magnetization measurements. The remanent magnetization is shown to arise from an interplay of the RKKY and dipolar forces. Magnetoresistivity results are found to be consistent with the aforementioned picture. The nature of magnetic interactions in an amorphous matrix is also discussed. The moment per Gd atom (7µ_B) is found to be constant and close to that of the crystalline value throughout the concentration range investigated. Finally, a detail study is made of the critical phenomena and magnetic properties of the amorphous ferromagnet: Gd₈₀Au₂₀. The results are compared with recent theories on amorphous magnetism.

Growth and spectral properties of Er:Gd2SiO5 crystal

Er3+ -doped Gd2SiO5 (Er:GSO) single crystal with dimensions of circle divide 35 x 40 mm(3) has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd-Ofelt theory, and the intensity parameters Omega(2), Omega(4) and Omega 6 are obtained to be 6.168 x 10(-20), 1.878 x 10(-20), and 1.255 x 10(-20) cm(2), respectively. The emission cross-section has been calculated by Fuechtbauer-Ladenbury formula. (c) 2007 Elsevier B.V. All rights reserved.

(Ga, Gd, As) film growth on GaAs substrate by low-energy ion-beam deposit

(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

1.3 mu m InAs/GaAs self-assembled quantum dots grown on In0.2Ga0.8As-GaAs combined strain-buffer layer

Optical properties and surface structures of InAs/CaAs self-assembled quantum dots (QDs) grown on 2 nm In-0.2 Ga0.8As and x ML GaAs combined strain-buffer layer were investigated systematically by photoluminescence ( PL) and atomic force microscopy (AFM). The QD density increased from similar to 1.7 x 10(9) cm(-2) to similar to 3.8 x 10(9) cm(-1) due to the decreasing of the lattice mismatch. The combined layer was of benefit to increasing In incorporated into dots and the average height-to-width ratios, which resulted in the red-shift of the emission peaks. For the sample of x = 10 ML, the ground state transition is shifted to 1350 nm at room temperature.

Mossbauer spectroscopy study of Fe-57 in R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

Fe-57 Mossbauer spectra for the Fe atoms in the R3Fe29-xTx (R=Y, Ce, Nd, Sm, Gd, Tb, Dy; T=V, Cr) compounds were collected at 4.2 K. The analysis of Mossbauer spectra was based on the results of magnetization and neutron powder diffraction measurements. The average Fe magnetic moments at 4.2 K, deduced from our data, are in accord with magnetization measurements. The average hyperfine field of Tb3Fe29-xCrx (x=1.0, 1.5, 2.0, and 3.0) decreases with increasing Cr concentration, which is also in accordance with the variation of the average Fe magnetic moment in the Tb3Fe29-xCrx compounds.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

Structural and magnetic properties of hydrides R3Fe29-xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R3Fe29 - xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants a, b, and c and the unit cell volume of R3Fe29 - xVxHy decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce3Fe27.5V1.5H6.5, like Ce3Fe27.5V1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce3Fe27.5V1.5 and Gd3Fe28.4V0.6 show the larger storage of hydrogen with y = 6.5 and 6.9 in these hydrides. (C) 1998 Elsevier Science B.V. All rights reserved.

Crystallographic and magnetic properties of R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

P_(507)萃取分离Gd、Tb、Dy三出口工艺及多元稀土萃取分离数学模拟的研究

溶剂分馏萃取是分离、提纯、富集物质的有效方法之一，由于它具有分离效果好，易于操作等优点。因此，在稀土萃取分离工艺中得到了广泛的应用。但是，每个分馏萃取工艺只能分离两个组份，若要分离所有稀土元素，流程较长。为改进生产，本工作提出了一种三出口萃取分离工艺流程。这种工艺流程可视为由两个萃取段和两个洗涤段组成，由于在两个洗涤段中，两相稀土浓度较高、稀土交换量较大，故可使级数减少。采用此工艺流程进行了P_(507)萃取分离Gd、Tb、Dy三组元素的串级模拟实验，得到了纯度大于99.99％的La－Gd，纯度大于99.8％的Dy－Lu和含量高于65％的Tb_4O_2富集物。Tb的收率大于95％。串级总级数为38级。通过对P_(507)萃取实际体系中稀土元素行为的研究，建立了多元体系中稀土在两相分配的经验模型。Z＝C_1H~(C2)×T~(C_3)e~(c_4X(Tb)+C_5X(Dy))和具有一定物理意义的半热力学半经验模型。YT=(Z/H)~3[Σ from i=1 to m of CiXi + Co]根据氨化P_(507)萃取工艺中稀土总浓度在两相的分布规律，提出了一种适合氨化P_(507)萃取分离多元混合稀土工艺的串级计算方法，并用FORTRAN语言编写 了计算程序。使用自编的计算程序进行了氨化P_(507)萃取分离Gd、Tb、Dy三出口工艺的串级模拟计算，计算结果与实验值基本一致。同时，对文献中报导的中间某级开设出口的一分三工艺也进行了串级计算，根据计算结果讨论了两种工艺的优缺点。对恒定混合萃取比的多元稀土萃取分离工艺，进行了在不同串级条件下分界元素在各级的积累及易萃组份和难萃取份的有效分离系数在各级变化规律的计算。结果表明，有效分离系数在级体中出现一极小值β~*，并且β~*值的大小与其出现在级体中的位置随条件不同而改变。对同一萃取体系，当出口产品较纯时，用线性回归分析法关联计算数据得到了β~*与出口产品组成和总萃取比的经验关系式，在萃取段有（A、B与C分离的工艺）β~*/β_B~C=C1+C2EM+C_3ln (A1)/(B1)引入有效分离系数后，进行了环烷酸萃取分离钇与镧系元素的串级模拟计算，计算结果与实验值基本吻合。

Ce~(3+)在复合氟化物基质中的发光研究

采用高温固相反应合成了K_5LnLi_2F_(10):Ce (Ln = La, Ce, Gd, Y)体系，K_2NaAlF_6:Ce和KAlF_4:Ce体系、MAlF_5:Ce(M = Ca, Sr, Ba)体系及ABF_3:Ce (A = Li, Na, K, B = Mg, Ca, Sr, Ba, Zn)体系的磷光体，同时，对SrAlF_5:Ce和BaAlF_5:Ce还采用沉淀法合成。生长3BaAlF_5:Ce和SrAlF_5:Ce的单晶。用X－射线衍射法检验了粉末基质的结构，用X－射线四元衍射仪解出了SrAlF_5单晶的结构，即属于四方晶系，空间群为I 4－bar, z = 8，晶胞参数为14.035 A和7.146 A。并测定了各体系磷光体的激发光谱和发射光谱，对BaAlF_5:Ce单晶还测定了吸收光谱和反射光谱。得到了Ce~(3+)在复合氟化物基质中发光的某些规律。Ce~(3+)激活的复合氟化物磷光体由于Ce-F键存在较强的离子性而具有紫外发光特征。Ce~(3+)激活的K_5LnLi_2F_(10)磷光体，由于基质结构的特殊性，使得Ce~(3+)发射波长几乎不随Ln~(3+)的改变而变化和计量比的K_5CeLi_2F_(10)发光体的浓度猝灭小。在同结构的ABF_3:Ce磷光体中，随着基质阳离子的φ~(1/2) = (z·α·X/γ)~(1/2)(z为电荷，α为极化率，X为电负性，γ为半径）值增大，其发射峰兰移。其原因是φ~(1/2)值增加，使Ce-F键的性质发性了改变，从而导致了Ce~(3+)的激发态与基态的能级差增加。Ce~(3+)在复合氟化物中，主要取代离子本性（半径，电荷，电负性等）与其相近的基质阳离子。但Ce~(3+)在AMgF_3(A = Na~+,K~+)基质中，同时可以取代A~+或Mg~(2+)离子，形成两种不同的发光中心。Ce~(3+)在SrAlF_5晶体中，由于取代两种不同格位的Sr~(2+)离子，也形成两种不同的发光中心，由于两种发光中心的性质不同，所以，它们的光谱结构明显不同。BaAlF_5:Ce和SrAlF_5:Ce晶体的光谱数据为设计Ce~(3+)的5d-4f跃迁的可调谐激光晶体材料提供了必要的、可靠的实验数据。

D_Y~(3+),Eu~(3+)激活铌酸盐的光谱性质

本论文围绕铌多元复合氧化物体系的合成、其质光谱性质及基质结构等进行了讨论，对于铌酸盐基质的敏化机理，D_Y~(3+)激活M_2O·Ln_2O_3·2Nb_2O_5(M=Li,Na,K,Ln=La,Gd,Y)、M_3LnNb_3O_(12)(M=Ca,Sr,Ba;Ln=La,Gd,Y),M~IM_2~(II)Nb_5O_(15)(M~I=Li,Na,K,M~(II)=Sr,Ba)等铌酸盐的质光强变及其超灵敏跃适特性，Eu~(3+)激活了上部分铌酸盐的荧光性质等也进行了研究。对M_2O·La_2O_3·2Nb_2O_5,M_3LaNb_3O_2及M~IBa_2Nb_5O_(15)等铌酸基质光谱性质研究结果表明在室温条件下基质荧光的产生与基质结构存在很大关系。通过实验发现铌酸盐基质体系中铌酸根之间相互连结方式是决定其能否产生荧光的重要因素。以D_Y~(3+)和Eu~(3+)做为激活剂，对其分别激活铌酸盐的荧光性质进行了研究。通过比较D_Y~(3+)和Eu~(3+)激活M_2o_3·2Nb_2O_5与M_3LnNb_3O_(12)、M~IM_2~(II)Nb_5O_(15)的荧光强度发现激活剂的发光效率与基质光谱之间存在一定关系。试验结果表明：M_2O·Ln_2o_3·2Nb_2O_5对D_Y~(3+)及Eu~(3+)具有较强的敏化作用，而在M_3LaNb_3O_(12)以及M~IM_2~(II)Nb_5O_(15)体系中D_Y~(3+)和Eu~(3+)的荧光强度极低，对此给出了定性的结论。对D_Y~(3+）超灵敏跃过现象进行了研究，并且得出一些实验规律。通过实验结果我们发现在所研究的铌酸盐体系中，D_Y~(3+)的超灵敏跃过强度随其掺杂系中周围环境的改变而发生变化。D_Y~(3+)掺杂M_2O·La_2O·2Nb_2O_5及M_3LaNb_3O_(12)荧光材料发射强度比的变化结果表明体系中M离子的改变对D_Y~(3+)的超灵敏跃过产生较为明显的影响。这是由于D_Y~(3+)周围环境极化程度的改变造成的。此外对D_Y~(3+)分别激活CaNb_2O_6及Ca_2Nb_2O_7的荧光特性进行了分析。在以Eu~(3+)的荧光做为结构探讨确定取代后D_Y~(3+)的空间检位。用实验结果观察环在掺杂的基质中D_Y~(3+)所处空间格位的对称性质对其超灵敏跃过也产生一定的影响。除此之外，在以上工作的基础上对D_Y~(3+)激活的二基色荧光材科也进行了研究。

Electronic structure and magnetic coupling properties of Gd-doped AlN: first-principles calculations

In this work, the electronic structure and magnetic coupling properties of Gd doped AlN have been investigated using first-principles method. We found that in the AlN:Gd system, due to the s-f coupling allowed by the symmetry, the exchange splitting of the conduction band is much larger than that of the valence band, which makes the electron-mediated ferromagnetism possible in this material. This property is also confirmed by the energy differences between anti-ferromagnetic and ferromagnetic phase for Al14Gd2N16 with different concentrations of electrons (holes), as well as by the calculated exchange constants. The result indicates that Gd-doped AlN is a promising candidate for the applications in future spintronic devices.