Nuclear orientation study of160Tb impurity in gadolinium single crystal

The low temperature nuclear orientation of¹⁶⁰Tb in gadolinium single crystal has been studied in the temperature range 5–60 mK and in the external magnetic field B_ext ≤9 T, applied both in the a- and c-axis directions. The obtained results indicate the noncollinearity between the Tb magnetic moments and the magnetization of the gadolinium matrix.     

160Tb nuclear orientation in yttrium single crystal

First experimental results of¹⁶⁰Tb nuclear orientation in yttrium single crystal matrix are described. The influence of external magnetic field in combination with the crystal field interaction is discussed.     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.     

Nuclear orientation study of155Tb decay

The angular distribution of gamma-rays following the electron capture decay of¹⁵⁵Tb nuclei oriented in a gadolinium host has been studied at temperatures between 16 and 80 mK. The magnetic dipole hyperfine splitting parameter for¹⁵⁵Tb(Gd) has been deduced and the value of the magnetic dipole moment of¹⁵⁵Tb ground state has been found to be=2.0(2) _N. The multipole mixing ratios have been determined for 9 gamma-transitions in¹⁵⁵Gd.On leave fromthe Department of Physics, University of Jyväskylä, Finland.The authors are indebted to Dr. N. A.Lebedev and to the mass-separator group of Nuclear spectroscopy and radiochemistry department at JINR for preparing the¹⁵⁵Tb activity. The assistance of Ing. M.I.Fominikh and Ing. P.Brada in computer analysis of spectra should be acknowledged. Organisation support of Dr. V. M.Tsupko-Sitnikov and his permanent interest during the course of our work is to be recognized here.     

Nuclear orientation of the rare-earth system^{160} Tb\underline {Tb} (sc)

We report precision nuclear orientation measurements on a bulk¹⁶⁰TbTb single crystal sample. The results of these experiments allow us to determine the hyperfine parameters for this system, as well as precise multipole mixing ratios for 22 gamma rays from the¹⁶⁰Dy daughter nucleus. Various methods of extracting the mixing ratios will be compared.     

Nuclear orientation of152,154Tb in gadolinium

The anisotropy in the directional distribution of gamma-rays from the decay of^152,154Tb oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction at temperature of (15±1) mK. Unambiguous values of spin have been deduced for several levels in¹⁵²Gd. Multipole mixing ratios of many gamma-ray transitions occurring in¹⁵²Gd have been found and results are compared with the similar transitions in^150,154,156Gd and they are discussed in terms of the rotational-vibrational model and dynamic deformation theory based on the Strutinsky method. Our results confirm the spin value of 0 for 21·4 h isomer in¹⁵⁴Tb and they establish the spin value of 3 for the 2277·0 and 2336·1 keV levels and the spin value of 4 for the 2416·3 keV level in¹⁵⁴Gd.     

Nuclear orientation of156Tb in gadolinium matrix

The anisotropy of the angular distribution of gamma-rays from the decay of¹⁵⁶Tb, oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction in the range of temperatures from 14·6 to 68·4 mK. The temperature dependence of anisotropy was measured for the first time. The parameters of hyperfine magnetic dipole and electric quadrupole splittings have been determined and the values of the magnetic dipole moment ¦Μ¹⁵⁶¦=(9·6±1·3)×10^?27 J/T and the electric quadrupole momentQ ¹⁵⁶=(2·9±0·9)×10^?28 m² of the¹⁵⁶Tb ground state have been calculated. Multipole mixing ratios andB(E2) branching ratios of many gamma-ray transitions occurring in¹⁵⁶Gd have been found and the results have been discussed in terms of the rotational-vibration and pairing-plus-quadrupole models.     

Nuclear orientation study of54Mn impurity in Pt100-x Fe x alloy

The low temperature nuclear orientation of⁵⁴Mn in Pt_99.95Fe_0.05, Pt_99.9Fe_0.1, Pt₉₉Fe₁ and Pt₈₈Fe₁₂ has been studied in the temperature range 12–50 mK and in the external magnetic field range 0–1.2 T. The strong temperature and external magnetic field dependence of the effective fieldB _eff on⁵⁴Mn has been observed even in the range where the host itself is magnetically saturated. This behaviour is interpreted by noncollinearity of the Mn magnetic moments with respect to the macroscopic magnetisation direction.     

Nuclear alignment of implanted160Tb in highly oriented pyrolytic graphite layers

Low-temperature nuclear alignment of¹⁶⁰Tb ions implanted in Highly Oriented Pyrolytic Graphite has been observed by the anisotropic intensity distribution of γ-rays. The data can be understood with an effective spin Hamiltonian containing combined magnetic and electric hyperfine interactions. Values deduced for the hyperfine parameters are A/k=(101±7) mK for the magnetic interaction, and P/k=(−3.7±0.9) mK for the nuclear electric quadrupole interaction, under the assumption that B=0 and Δ=0. Measurements in magnetic fields of 0.2 and 1.0 T directed along the graphite c-axis showed thermal saturation due to the strongly reduced heat conductivity of HOPG in the presence of a magnetic field.     

Magnetostriction in LaAg single crystal with Tb impurities

We have made magnetostriction measurements on a La_0.99Tb_0.01Ag single crystal at low temperature. The shape magnetostriction dominates, and the 〈001〉 and 〈111〉 effects have opposite signs. The volume magnetostriction is positive but small. We analyse the results in a single-ion model, using the crystal-field parameters suggested by Hoenig et al., and we deduce the orbit-lattice coupling parameters V³₂ and V⁵₂. Results are compared with those in other cubic metallic systems containing rare earths.     

Nuclear orientation study of low temperature magnetization of54Mn impurity in ferromagnetic PtFe alloys

Low-temperature nuclear orientation of⁵⁴Mn in ferromagnetic Pt₉₅Fe₅ and Pt₉₀Fe₁₀ hosts has been investigated in 12–50 mK temperature range at external magnetic fields up to 1.2 T. Temperature dependence of the effective magnetic field B_eff on Mn has been observed and interpreted as an effect of misalignment of Mn magnetic moments with respect to the macroscopic magnetization direction at host magnetic saturation.     

Magnetic behaviour of Tb impurities in Gd andY single crystals: a nuclear orientation study

The low temperature nuclear orientation of¹⁶⁰Tb impurities in Gd andY single crystals has been studied in the temperature range 7–40 mK andin the external magnetic field range 0–7.3 T applied alonga-, b- andc-crystal axes. In the case of Tb in Gd we found a considerable noncollinearity of the Tb magnetic moment with respect to the magnetic external field direction even for highB _ext. In the case of Tb in Y the results cannot be described by a simple model, taking into account the simultaneous influence of the crystal andexternal magnetic fields. Some new proposals for interpretation of the experimental dat are given.     

单晶合金激光熔凝过程中晶向对单晶完整性的影响

运用几何模型对单晶合金激光熔凝过程中激光扫描方向与[100]方向夹角ξ变化时熔池内的枝晶生长方向和速度进行了计算,研究了ξ增大时不同晶向区域的分布变化规律.发现随着ξ的增大, 0]区域增大,[010]区域减小,且熔池两边不同部分速度差别增强.根据速度变化规律,构造出了熔池不同部位的过冷区域变化图,说明了可能出现新晶粒的趋势变化,并与实验结果进行了比较,揭示了在晶向不同的交界区域产生新晶粒的内在机理. 关键词： 单晶合金 激光熔凝 晶向 组成过冷     

The CNDO-MO study of oxygen impurity states in AlN crystal

Deep levels due to oxygen impurity have been theoretically studied by the quasimolecular approach. The calculation of the orbital spectra was performed using the CNDO/2 method. Some important quantities (transition energies, width of valence band, effective charges etc.) were estimated. The results obtained agree qualitatively well with experimental data but quantitatively are still about 20% in error. Some reasons for the above discrepancy are briefly discussed.The authors are very grateful to Dr. J.Kubátová and Dr. S.Paesová for helpful discussions of the experimental investigations of aluminum nitride and to Dr. J.Pastrák for his interest in this work and discussion of results.     

高纯硅中补偿性杂质的光热电离光谱

首先测量了高纯n型硅样品在接近液氦温度区域内随温度变化的光热电离光谱，确定了硅样品的最佳光热电离温度范围. 在该温度范围内，在有本征带隙光照射条件下，测量了样品的高分辨率光热电离光谱，同时观察到了来自主要浅杂质施主磷以及补偿性杂质硼的正信号. 随后，应用外加磁场，对硼的光热电离光谱进行了研究，发现来自硼的光热电离信号，在外加磁场作用下，发生了由正向负信号的转变. 通过对该现象进行分析讨论，排除了该现象是温度效应的可能，指出普遍用来解释补偿性杂质光热电离响应的Darken模型存在不足，而少数载流子快速复合模     

高纯硅中补偿性杂质的光热电离光谱

首先测量了高纯n型硅样品在接近液氦温度区域内随温度变化的光热电离光谱,确定了硅样品的最佳光热电离温度范围. 在该温度范围内,在有本征带隙光照射条件下,测量了样品的高分辨率光热电离光谱,同时观察到了来自主要浅杂质施主磷以及补偿性杂质硼的正信号. 随后,应用外加磁场,对硼的光热电离光谱进行了研究,发现来自硼的光热电离信号,在外加磁场作用下,发生了由正向负信号的转变. 通过对该现象进行分析讨论,排除了该现象是温度效应的可能,指出普遍用来解释补偿性杂质光热电离响应的Darken模型存在不足,而少数载流子快速复合模 关键词： 高纯硅 光热电离光谱 元素半导体中的杂质和缺陷能级 少数载流子快速复合     

EPR and optical absorption studies of vanadyl impurity in lithium hydrogen oxalate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of vanadyl ions in lithium hydrogen oxalate monohydrate single crystal and powder are reported at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes, $a{b}^1$, $b^1{c}^1$ and $a{c}^1$ indicate four different vanadyl complexes. The detailed investigation of EPR spectra indicates that one of the VO^{2 +} sites (the intense one) may enter the lattice substitutionally and the other three occupy the interstitial positions. From the angular variation, the spin Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum shows four bands. From the optical and EPR data, various bonding parameters are determined and the nature of bonding in the crystal is discussed.