Probing the magnetic state by linear and non-linear ac magnetic susceptibility measurements in under-doped manganite Nd0.8Sr0.2MnO3

We have thoroughly investigated the entire magnetic states of under-doped ferromagnetic-insulating manganite Nd_0.8Sr_0.2MnO₃ through temperature-dependent linear and non-linear complex ac magnetic susceptibility measurements. This ferromagnetic-insulating manganite is found to have frequency-independent ferromagnetic to paramagnetic transition temperature at around 140 K. At around 90 K (≈T_?) the sample shows a second frequency-dependent re-entrant magnetic transition as explored through complex ac susceptibility measurements. Non-linear ac susceptibility measurements (higher harmonics of ac susceptibility) have also been performed (with and without the superposition of a dc magnetic field) to further investigate the origin of this frequency dependence (dynamic behavior at this re-entrant magnetic transition). Divergence of 3rd harmonic of ac susceptibility in the limit of zero exciting field indicates a spin-glass-like freezing phenomena. However, large value of spin-relaxation time (τ₀=10⁻⁸ s) and small value of coercivity (∼22 Oe) obtained at low temperature (below T_?) from critical slowing down model and dc magnetic measurements, respectively, are in contrast with what generally observed in a canonical spin glass (τ₀=10⁻¹²-10⁻¹⁴ s and very large value of coercivity below freezing temperature). We have attributed our observation to the formation of finite size ferromagnetic clusters which are formed as consequence of intrinsic phase separation and undergo cluster glass-like freezing below certain temperature in this under-doped manganite. The results are supported by the electronic- and magneto-transport data.     

偶极-偶极相互作用下双势阱中旋量玻色-爱因斯坦凝聚磁化率的非线性动力学性质

利用平均场理论和单空间模近似，研究了偶极-偶极相互作用下双势阱中总自旋F=1的旋量玻色-爱因斯坦凝聚磁化率的非线性动力学性质.在给定的初态条件下，研究结果表明：当λ_A+2λ_d=0时，凝聚体只表现为磁化振荡行为；当λ_A+2λ_d≠0时，凝聚体既存在磁化振荡行为，又存在磁自陷俘现象. 关键词： 玻色-爱因斯坦凝聚 自旋 磁化率     

Effect of magnetic field on the spin-Peierls transition in single-crystal CuGeO

This paper reports that high quality CuGeO3 single crystals were successfully grown by floating-zone technique and the magnetic property was studied. The temperature dependence of magnetic susceptibility below the spin-Peierls （SP） transition temperature （Tsp） under magnetic fields applying along both the a- and c-axis direction can be fitted well by a model of noninteracting dimmers. The spin gap derived from the fitting is consistent with other reports. There is a very weak anisotropy in the fitting parameters for different directions, which should be expected from a SP system. A small upturn in susceptibility at low temperature due to paramagnetic impurities and/or defects can be observed. A suppression of the upturn by magnetic field is first discovered in this system and the possible origins for this suppression are discussed.     

Errata and Addendum: Magnetic properties of an antiferromagnetic spin-1/2 XYZ model in the presence of different magnetic fields: finite-size effects of inhomogeneity property (2019, Commun. Theor. Phys. 71 1253–1260)

We report the correct results for the antiferromagnetic s = 1/2 XYZ model system considered in (2019, Commun. Theor. Phys. 71 1253). We also point out the correct model system used for the reported results therein.     

Grazing-induced crises in hybrid dynamical systems

In hybrid dynamical systems including both continuous and discrete components, an interplay between a continuous trajectory and a discontinuity boundary can trigger a sudden qualitative change in the system dynamics. Grazing phenomena, which occur when a continuous trajectory hits a boundary tangentially, are well known as a representative of such phenomena. We demonstrate that a grazing phenomenon of a chaotic attractor can result in its sudden disappearance and initiate chaotic transients. The mechanism of this grazing-induced crisis is revealed in an illustrative example. Furthermore, we derive a formula to obtain the critical exponent of the power law on the mean duration of chaotic transients.     

永磁性大块金属玻璃Nd60Al10Fe20Co10低温磁性的研究

研究了Nd6 0 Al1 0 Fe2 0 Co1 0 大块金属玻璃磁性随温度的变化关系 ,结果表明Nd6 0 Al1 0 Fe2 0 Co1 0 在室温下表现为永磁性 ,随着温度的降低 ,矫顽力和磁滞回线形状都有很大的变化 .交流磁化率在 18K左右出现尖峰而且峰值温度随频率变化 ,表明该大块非晶体系中存在自旋玻璃态     

Zn掺杂La2CuO4热电势和磁化率研究

测量了La2CuO4掺Zn样品在不同降温速率下(330K保温05h,然后分别以6Kh,02Ks的速度降到8K)的直流磁化率和热电势.实验结果表明,反铁磁温度TN不随降温速率变化而变化,其直流磁化率也未受很大影响.高温热电势弱的温度依赖关系表明为极化子气体的贡献.热电势在转折温度Tdrop之下的快速降低是由于二维反铁磁涨落的贡献.热电势在更低温度的拐点TS与载流子的局域化有关.降温速率变化时,Tdrop和TS都有明显的变化.Zn掺杂对Tdrop和TS没有明显影响,但导致了更强的载流子局域化.讨论了上述现象产生的物理图像 关键词： La2CuO4 直流磁化率 热电势     

Spin waves on the surface of the nonferromagnetic nanotube in magnetic field

Propagating in the nonferromagnetic electron gas on the cylindrical nanotube's surface spin waves in longitudinal magnetic field are considered. The spectrum of electrons in the Hartree-Fock approximation was applied. The dynamic spin susceptibility of a degenerate electron gas was derived using the random phase approximation. The spectra of intra-subband and inter-subband magnons were calculated in quasiclassical and quantum limits. The quantity of spin waves spectrum branches depends on the amount of filled subbands. In case the filled subband numbers are large, the wave's frequencies undergo oscillations of de Haas-van Alphen and Aharonov-Bohm types with the electron density and the magnetic induction changes.     

High temperature magnetic order in zinc sulfide doped with copper

We report the first observation of magnetic order above room temperature in zinc sulfide doped with Cu²⁺ made by a simple sintering process and detected by ferromagnetic resonance (FMR), SQUID magnetometry and the μSR experiments. FMR study shows nonzero absorption above room temperature indicating a high value of Curie temperature. Field-cooled and zero-field-cooled magnetization data indicate a bifurcation at about 300 K. This temperature is considered to be the blocking temperature at ferromagnetic nanosized regions, which appear to exist in the sample of ZnS doped with copper. The muon spin rotation measurements confirm highly nonuniform magnetic order. It was shown that about 25% of the sample volume fraction exhibits strong magnetism.     

ESR studies of Cu2+ doped in triglycine calcium bromide single crystals

Electron spin resonance studies were carried out on Cu²⁺ doped triglycine calcium bromide. The spectra recorded at room temperature revealed well-resolved hyperfine spectra of⁶³Cu superposed with super-hyperfine lines due to¹⁴N nuclei. The spin Hamiltonian parameters are evaluated. It was concluded that the Cu²⁺ enters the lattice interstitially.     

{Cu3}单分子磁体在磁场中的热纠缠

本文研究单分子磁体Na₉[Cu₃Na₃(H₂O)₉ (α-AsW₉O₃₃)₂]·26H₂O中三角自旋 环在磁场作用下的热纠缠性质, 利用数值计算求出任意两个Cu²⁺离子量子比特之间的配对纠缠度, 分别记为C₁₂, C₂₃和C₁₃. 研究结果表明, 磁场的方向和大小以及温度对配对纠缠度具有重要影响, 而且参数的变化对C₁₂, C₂₃和C₁₃的影响也是各不相同. 给出外加三个不同方向的磁场时, 配对纠缠度C₁₂, C₂₃和C₁₃各自对应的临界温度T_c随磁场强度的变化图, 由此可以得到单分子磁体三角自旋环中存在纠缠态的参数范围. 通过选择适当的磁场方向和大小以及温度等实验参数, 可以有效地调节和提高单分子磁体中的配对纠缠度. 关键词： 配对纠缠 单分子磁体 三角自旋环     

Cu掺杂ZnO稀磁半导体磁电性能影响的模拟计算

在Cu重掺杂量摩尔数为0.02778–0.16667的范围内, 对ZnO掺杂体系磁电性能影响的第一性原理研究鲜见报道. 采用基于自旋密度泛函理论的平面波超软赝势方法, 用第一性原理计算了两种不同Cu单掺杂量Zn_1-xCu_xO (x=0.02778, 0.03125)超胞的能带结构分布和态密度分布. 结果表明, 掺杂体系是半金属化的稀磁半导体; Cu掺杂量越增加、相对自由空穴浓度越增加、空穴有效质量越减小、电子迁移率越减小、电子电导率越增加. 此结果利用电离能和Bohr半径进一步获得了证明, 计算结果与实验结果相符合. 在限定的掺杂量0.02778–0.0625 的条件下, Cu单掺杂量越增加、掺杂体系的体积越减小、总能量越升高、稳定性越下降、形成能越升高、掺杂越难. 在相同掺杂量、不同有序占位Cu双掺ZnO体系的条件下, 双掺杂Cu-Cu间距越增加, 掺杂体系磁矩先增加后减小; 当沿偏a轴或b轴方向Cu–O–Cu相近邻成键时, 掺杂体系会引起磁性猝灭; 当沿偏c轴方向Cu–O–Cu相近邻成键时, 掺杂体系居里温度能够达到室温以上的要求. 在限定的掺杂量0.0625–0.16667的条件下, 沿偏c轴方向Cu–O–Cu相近邻成键时, Cu 双掺杂量越增加, 掺杂体系总磁矩先增加后减小. 计算结果与实验结果变化趋势相符合.     

自旋相关的电子隧穿和自旋极化

研究了电子的自旋相关的隧穿和极化。在外加磁场的作用下，自旋向上的电子与自旋向下的电子具有不同的隧穿系数。当电子的自旋方向与磁场方向相反时，其隧穿概率受到磁场的抑制而变小；反之，当两平行时，电子的了隧穿系数增大。这种差异可以用本中定义的自旋极化率来表示。本对不同磁场下的自旋极化率进行了计算，结果也表明当电子的动能较小，这种自旋极化的效应越显。     

Thermoelectric power and magnetic properties of Cu doped NiZn ferrite for technological application

A series of samples in the system Ni_0.65Zn_0.35Cu_xFe_2-xO₄ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the usual ceramic technique. The thermoelectric power and the magnetic susceptibility were measured. The transition from the ferrimagnetic to the paramagnetic state is accompanied by an increase in the thermo EMF. NiZn ferrite shows n-type conductivity due to the presence of Fe²⁺ ions. The addition of Cu²⁺ ions creates lattice vacancies which give rise to p-type conductivity.

The Tawfik coefficient was determined for NiZn ferrite in the paramagnetic state. This coefficient was reduced by addition of Cu up to x < 0.5.     

Synthesis and magnetic properties of Li-Mn-Zn spinel oxides

LiMn_2−XZn_XO₄ (X<0.5) compounds were prepared by sol-gel method. The specimens with a large substitution degree (X>0.2) led to symmetry reduction from Fdm to P2₁3 in the spinel oxide, while those with a small substitution degree (X<0.1) had Fdm cubic symmetry. The Zn²⁺-substitution led to the enhancement of the low-temperature magnetic susceptibility and a shift in the Weiss constant from negative to positive, indicating that the dominant exchange interaction changed from antiferromagnetic to ferromagnetic. For the compounds with X=0.5, the spontaneous magnetization was 4.48μ_B and the Curie temperature was approximately 21 K. The experimentally obtained magnetization value was close to the value calculated under the assumption that the spins of the Mn⁴⁺ ions were aligned in ferromagnetic form. In addition, the magnetic properties of Li-Mn-Zn spinel oxides were briefly discussed, and compared with those of Li-Mn-M (M=Ni, Mg) spinel oxides.     

Structural,morphological, magnetic and dielectric characterization of nano-phased antimony doped manganese zinc ferrites

Nano-phased doped Mn–Zn ferrites, viz., Mn_0.5−x/2Zn_0.5−x/2Sb_XFe₂O₄ for x=0 to 0.3 (in steps of 0.05) prepared by hydrothermal method are characterized by X-ray diffraction, Infrared and scanning electron microscopy. XRD and SEM infer the growth of nano-crystalline cubic and hematite (α-Fe₂O₃) phase structures. IR reveals the ferrite phase abundance and metal ion replacement with dopant. Decreasing trend of lattice constant with dopant reflects the preferential replacement of Fe³⁺ions by Sb⁵⁺ion. Doping is found to cause for the decrease (i.e., 46–14 nm) of grain size. An overall trend of decreasing saturation magnetization is observed with doping. Low magnetization is attributed to the diamagnetic nature of dopant, abundance of hematite (α-Fe₂O₃) phase, non-stoichiometry and low temperature (800 °C) sintering conditions. Increasing Yafet–Kittel angle reflects surface spin canting to pronounce lower M_s. Lower coercivity is observed for x≤0.1, while a large H_c results for higher concentrations. High ac resistivity (~10⁶ ohm-cm) and low dielectric loss factor (tan δ~10⁻²–10⁻³) are witnessed. Resistivity is explained on the base of a transformation in the Metal Cation-to-Oxide anion bond configuration and blockade of conductivity path. Retarded hopping (between adjacent B-sites) of carriers across the grain boundaries is addressed. Relatively higher resistivity and low dielectric loss in Sbdoped Mn–Zn ferrite systems pronounce their utility in high frequency applications.     

Static and dynamical distortions of helium clusters

We examine the effects of impurities (doping) and rotational excitation on the structural and energetic properties of helium clusters. Quantum Monte Carlo (QMC) techniques are used to study ground and rotationally excited states of pure and doped clusters. We use exponentially correlated wave functions and treat the molecular impurities as rigid. Whereas pure He_N show essentially monotonic decay of density from a central maximum value, addition of impurities induces local ordering of He to an extent dependent on the impurity-He binding. Rotational excitation of He_N gives rise to extremely large centrifugal distortions. The location of impurities also appears to change upon rotational excitation. The implications of these distortions on impurity spectra are discussed for SF₆He_N, and compared to recent experimental results.     

Theoretical investigation of the spin-Hamiltonian parameters and optical spectra for the doped Cu2+ in ZnCdO nanopowder

The spin-Hamiltonian (SH) parameters (g factors g_||, g_⊥ and hyperfine structure constants A_||, A_⊥) and d–d transitions for ZnCdO:Cu²⁺ are calculated based on the perturbation formulas for a 3d⁹ ion in tetragonally elongated octahedra. Good agreement between the calculated results (four SH parameters and three optical absorption bands) and the experimental results can be obtained. Since the SH parameters are sensitive to the local structure of a paramagnetic impurity center, the tetragonal distortion (characterized by the relative elongation ratio ρ ≈ 3.5% along the C₄ axis) of the impurity center due to the Jahn–Teller effect is also acquired from the calculations. The negative and positive signs of hyperfine structure constants A_|| and A_⊥ for ZnCdO:Cu²⁺, respectively, are also suggested in the discussions.     

Physical properties of magnetic grains dispersed in anisotropic media

We calculate the dynamical response of a group of non-interacting magnetic grains dispersed in a medium that imposes on them an uniaxial anisotropy. Numerical results are obtained for a collection of grains that has its volume distribution given by a Gaussian function centered in the average volume V₀, and has a width σV₀. We assume that the only effect of the medium on the particles is the anisotropy imposed on the grains to study the influence of the volume distribution (σ and V₀) on the effective permeability. The results are analyzed through the calculation of numerical values for the components of the magnetic permeability and also by the analysis of the combined effect of the external dc magnetic field and the width of the volume distribution on the skin depth.