Effect of pressure on magnetic phases of (Fe1-x Ni x )49Rh51

The effect of high pressure and magnetic field on the stability of magnetic phase transitions in (Fe_1?x Ni _x )₄₉Rh₅₁ has been studied. It has been shown that the increase in the Ni content suppresses the stability of the low-temperature antiferromagnetic phase and leads to its disappearance. Pressure on the other hand restores the stability to the antiferromagnetic order. These findings are explained using first-principles band-structure calculations.     

Large variations in the magnetic ordering behavior of EuCu(2)As(2) with the application of external pressure and magnetic field

The influence of external pressure on the electrical transport and magnetic properties of EuCu(2)As(2), crystallizing in a ThCr(2)Si(2)-type structure, is reported. The system is known to be an antiferromagnet below T(N) ≈ 15 K in the absence of external magnetic fields. We find that there is a gradual reduction of T(N) with the application of a magnetic field with an extrapolated value of the critical field of around 18 kOe which can drive T(N) to zero. Electrical resistivity under pressure (<11 GPa) reveals that the magnetic ordering temperature is pushed up dramatically to higher temperatures which is quite interesting if compared with the behavior in isostructural FeAs-based systems containing Eu. Above 7 GPa, the pressure-induced state appears to be ferromagnetic. The results thus reveal interesting changes in the magnetic ordering behavior of this compound with increasing pressure and magnetic fields.     

In-beam magnetization measurements of thin Fe foils and simultaneous observation of the transient magnetic field at Pd ions

The well established phenomenon of heavy ion beam induced attenuations of transient magnetic fields (TF) was studied by measuring the in-beam magnetization of bombarded Fe foils employing the magneto-optical Kerr-effect. Whereas the macroscopic magnetization did not show any deterioration, the simultaneously measured TF of recoiling¹⁰⁸Pd(2⁺) ions was found to be substantially attenuated.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

过渡金属Mn（Ⅲ）,Fe（Ⅲ）,Rh（Ⅱ）和Pd（Ⅱ）卟啉配合物的共振拉…

讨论了金属离子Ｍｎ（Ⅲ），Ｆｅ（Ⅲ），Ｒｈ（Ⅲ）和Ｐｄ（Ⅱ）原卟啉Ⅸ－二甲酯（ＰＰ）和四苯基卟啉（ＴＰＰ）配合物及Ｐｄ（Ⅱ）间氯四苯基卟啉（ＴＰＰｍ－ｃｌ）配合物的共振拉曼光谱。利用金属离子外层ｄ电子与卟啉环的作用，解释了配合物结构灵敏带的变化规律，同时讨论了不同卟啉及卟啉环上取代基团对结构灵敏带的影响。     

Determination of the magnetic structure of SmFe(3)(BO(3))(4) by neutron diffraction: comparison with other RFe(3)(BO(3))(4) iron borates

Temperature dependent neutron diffraction studies were performed on SmFe(3)(BO(3))(4). The crystallographic structure was determined to stay as R32 over the whole studied temperature range of 2?K?相似文献   

Phase transition in multiferroic YMnO3 and its solid solution YMn(0.93)Fe(0.07)O3

Ceramics of YMnO₃ and its Fe substituted YMn_(0.93)Fe_(0.07)O₃ solid solution were synthesized by solid state reaction of the oxides at 1200 °C. Hexagonal phase was identified in both cases by X-ray powder diffraction. Rietveld refinement of cell parameters showed an increase of the parameter values for the solid solution. Dielectric permittivity measurements versus temperature showed a phase transition at 655 °C for yttrium manganite, however, for the solid solution no phase transition was detected on heating up to 700 °C. Dielectric loss measurements showed higher slope changes and better defined local maxima for the solid solution than for the pure phase.     

Magnetic excitations and phase transition of CsFeBr3 in an external magnetic field

In CSFeBr₃ the Fe²⁺ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Landé factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgård describe the experimental results very well. At 4.1 Tesla a phase transition appears to a commensurate long range order with a 120° arrangement of the spins in the hexagonal plane. Within the limits of experimental observation this phase transition has no influence on the dynamical behaviour. No critical phenomena could be observed. The dynamical structure factor |G _j()|² of the lower Zeeman split modes decreases with increasing field.     

Novel pressure-induced magnetic transition in magnetite (Fe3O4)

Fe K-edge x-ray magnetic circular dichroism of magnetite (Fe3O4) powders was measured with synchrotron radiation under variable pressure and temperature conditions in diamond anvil cell. The magnetic dichroism was observed to decrease discontinuously by approximately 50% between 12 and 16 GPa, independent of temperature. The magnetic transition is attributed to a high-spin to intermediate-spin transition of Fe2+ ions in the octahedral sites and could account for previously observed structural and electrical anomalies in magnetite at this pressure range. The interpretation of x-ray magnetic circular dichroism data is supported by x-ray emission spectroscopy and theoretical cluster calculations.     

非金属N和过渡金属(Mo, Ru, Rh, Pd)掺杂SnO2磁性的第一性原理研究

本文基于第一性原理方法,对非金属元素(N)与过渡金属元素(Mo, Ru, Rh, Pd)掺杂SnO₂的电子结构和磁学性质进行计算分析.结果表明：形成能与过渡金属原子半径密切相关,随着过渡金属原子半径的增加,形成能在降低,其中N-Mo掺杂体系形成能最低,故该体系最容易掺杂形成;能带结构分析表明,由于掺杂体系自旋向上/向下杂质能级的数量和分布均不对称,掺杂体系均有磁性产生;进一步探究态密度可知,体系产生磁性的原因是过渡金属原子和N原子之间产生p-d轨道杂化,最外层电子轨道上的空位及单电子相互耦合所导致.结果表明,由于掺杂原子的引入,SnO₂体系产生磁性,并且掺杂体系呈现亚铁磁性,其中N-Rh掺杂体系的磁性最好,其磁矩为1.88μB,有望成为良好的稀磁半导体材料.     

Anomalous field dependence of the inverse magnetocaloric effect in Ce(Fe0.93Ru0.07)2

A summary of detailed isothermal magnetization along with the ac susceptibility measurements on Ce(Fe_0.93Ru_0.07)₂ is presented. Near the first-order transition, i.e. near 110 K, Ce(Fe_0.93Ru_0.07)₂ displays a large positive magnetic entropy change, ΔSm, of 7.8 J/kg K in fields of only 2 T, i.e. it displays a strong inverse magnetocaloric (MCE) effect, as expected, on entering an antiferromagnetic (AF) state. However, the variation of the magnitude and width of this entropy change with field are anomalous when compared with model predictions, the former increasing with applied field below 2 T, while the latter exceeds 60 K in a field of 8 T.     

Mass spectra and decay of mesons under strong external magnetic field

We study the mass spectra and decay process of σ and begin{document}$ pi_0 $end{document} mesons under a strong external magnetic field. To achieve this goal, we deduce the thermodynamic potential in a two-flavor, hot and magnetized Nambu–Jona-Lasinio model. We calculate the energy gap equation through the random phase approximation (RPA). Then we use the Ritus method to calculate the decay triangle diagram and self-energy in the presence of a constant magnetic field B. Our results indicate that the magnetic field has little influence on the mass of begin{document}$ pi_0 $end{document} at low temperatures. However, for quarks and σ mesons, their mass clearly changes, which reflects the influence of magnetic catalysis (MC). The presence of a magnetic field accelerates the decay of the meson while the presence of a chemical potential will decrease the decay process.     

高压下Fe从bcc到hcp结构相变机理的第一性原理计算

采用基于密度泛函理论的第一性原理方法, 分别研究了压力作用下Fe从体心立方 (bcc,α 相) 结构到六角密排(hcp, ε相) 结构相变的两种不同的相变机理: 相变过程中出现亚稳定的面心立方(fcc) 结构(bcc-fcc-hcp) , 以及相变过程中没有出现亚稳定的fcc结构(bcc-hcp) . 计算结果表明: 静水压力条件下, 相变过程中并不会产生亚稳定的fcc结构, 这与最近的原位XRD实验测量结果相一致. 随着压力的增加, fcc-hcp的相变势垒逐渐增加, 压力趋向于阻止Fe从fcc结构到hcp结构的相变. 计算得到了相变过程中原子磁性和结构的详细信息, 分析表明相变过程中涉及复杂的磁性转变, 并且讨论了原子磁性对结构转变影响的物理机理. 此外, 对分子动力学模拟中产生亚稳定的fcc结构的原因也进行了讨论. 关键词： 相变机理 静水压力 第一性原理 铁