共查询到20条相似文献,搜索用时 31 毫秒
1.
We report an additional reversal mechanism of magnetic vortex cores in nanodot elements driven by currents flowing perpendicular to the sample plane, occurring via dynamic transformations between two coupled edge solitons and bulk vortex solitons. This mechanism differs completely from the well-known switching process mediated by the creation and annihilation of vortex-antivortex pairs in terms of the associated topological solitons, energies, and spin-wave emissions. Strongly localized out-of-plane gyrotropic fields induced by the fast motion of the coupled edge solitons enable a magnetization dip that plays a crucial role in the formation of the reversed core magnetization. This work provides a deeper physical insight into the dynamic transformations of magnetic topological solitons in nanoelements. 相似文献
2.
The local density of states (LDOS) at the vortex lattice cores in a high- T(c) superconductor is studied by using a self-consistent mean-field theory including interactions for both antiferromagnetism (AF) and d-wave superconductivity (DSC). In a zero-field optimally doped sample the AF order is completely suppressed while DSC prevails. In the mixed state, we show that the local AF-like spin density wave order appears near the vortex core and acts as an effective local magnetic field on electrons via Zeeman coupling. As a result, the LDOS at the core exhibits a double-peak structure near the Fermi level that is in good agreement with recent scanning tunneling microscopy observations. 相似文献
3.
Raabe J Quitmann C Back CH Nolting F Johnson S Buehler C 《Physical review letters》2005,94(21):217204
We have measured the excitation spectrum of six micron magnetic squares using x-ray magnetic circular dichroism. We observe all three excitations expected in a Landau flux-closure pattern. High temporal and spatial resolution allows quantitative analysis of the excitations. A short magnetic in plane pulse excites the magnetic element and we observe precessional motion of the magnetization within the domains as well as a domain wall mode and vortex motion. The vortex moves perpendicular to the excitation field and relaxes without showing a circulating orbit. 相似文献
4.
A first-principles-based effective Hamiltonian is used to investigate finite-temperature properties of ferroelectric nanocomposites made of periodic arrays of ferroelectric nanowires embedded in a matrix formed by another ferroelectric material. Novel transitions and features related to flux-closure configurations are found. Examples include (i)?a vortex core transition, that is characterized by the change of the vortex cores from being axisymmetric to exhibiting a 'broken symmetry'; (ii)?translational mode of the vortex cores; (iii)?striking zigzag dipolar chains along the vortex core axis; and (iv)?phase-locking of ferroelectric vortices accompanied by ferroelectric antivortices. These complex phenomena are all found to coexist with a spontaneous electrical polarization aligned along the normal of the plane containing the vortices. 相似文献
5.
Spatially resolved NMR is used to probe the magnetism in and around vortex cores of nearly optimally doped Tl(2)Ba(2)CuO(6+delta) (T(c)=85 K). The NMR relaxation rate T(-1)1 at the 205Tl site provides direct evidence that the antiferromagnetic (AF) spin correlation is significantly enhanced in the vortex core region. In the core region Cu spins show a local AF ordering with moments parallel to the layers at T(N)=20 K. Above T(N) the core region is in the paramagnetic state which is a reminiscence of the state above the pseudogap temperature (T(*) approximately 120 K), indicating that the pseudogap disappears within cores. 相似文献
6.
We observe the dynamics of a single magnetic vortex pinned by a defect in a ferromagnetic film. At low excitation amplitudes, the vortex core gyrates about its equilibrium position with a frequency that is characteristic of a single pinning site. At high amplitudes, the frequency of gyration is determined by the magnetostatic energy of the entire vortex, which is confined in a micron-scale disk. We observe a sharp transition between these two amplitude regimes that is due to depinning of the vortex core from a local defect. The distribution of pinning sites is determined by mapping fluctuations in the frequency as the vortex core is displaced by a static in-plane magnetic field. 相似文献
7.
M. LoBue F. Mazaleyrat M. Ammar R. Barrué Y. Champion S. Faure M. H?tch E. Snoeck J. Steiner F. Alouges 《Journal of magnetism and magnetic materials》2010,322(9-12):1290-1292
We use an approximate micromagnetic model, based on geometrical simplifications of the problem, to describe the vortex core structure observed in spherical Permalloy nanoparticles using off-axis electron holography. The magnetisation distribution inside the vortex core is directly calculated by minimising the micromagnetic energy functional and is compared with the experimental results. The symmetry constraints underlying the model are discussed envisaging possible generalisation to the case of vortex cores with structure strongly dependent on the coordinate directed along the axis of the vortex. Moreover the many-body effect associated with the presence of two small satellite particles is described by rescaling the size of the particle. 相似文献
8.
感应脉冲加速器的磁芯通常为铁氧体或非晶材料,而感应腔磁芯在工作脉冲下的磁性能是决定感应加速脉冲波形好坏的重要因素。搭建了低压多脉冲实验平台对铁氧体和非晶小磁环分别进行MHz重复频率的多脉冲励磁,对励磁线圈上的电压电流波形进行监测,绘制了多脉冲励磁下磁环的磁化曲线,并结合含磁芯线圈动态电感量的递推公式计算出磁环在多脉冲励磁过程中磁导率的变化曲线;在高压三脉冲实验平台上对铁氧体磁芯和非晶磁芯实验感应腔进行了高压三脉冲实验,得到的磁芯多脉冲磁化规律与低压实验的结果一致。最后对两种磁环在多脉冲励磁下的磁性能差异进行了对比分析。 相似文献
9.
Miller RI Kiefl RF Brewer JH Sonier JE Chakhalian J Dunsiger S Morris GD Price AN Bonn DA Hardy WH Liang R 《Physical review letters》2002,88(13):137002
Evidence for static alternating magnetic fields in the vortex cores of underdoped YBa2Cu3O6+x is reported. Muon spin rotation measurements of the internal magnetic field distribution of the vortex state of YBa2Cu3O6.50 in applied fields of H = 1 T and H = 4 T reveal a feature in the high-field tail of the field distribution which is not present in optimally doped YBa2Cu3O6.95 and which fits well to a model with static magnetic fields in the vortex cores. The magnitude of the fields is estimated to be 18(2) G and decreases above T = 10 K. We discuss possible origins of the additional vortex core magnetism within the context of existing theories. 相似文献
10.
感应脉冲加速器的磁芯通常为铁氧体或非晶材料,而感应腔磁芯在工作脉冲下的磁性能是决定感应加速脉冲波形好坏的重要因素。搭建了低压多脉冲实验平台对铁氧体和非晶小磁环分别进行MHz重复频率的多脉冲励磁,对励磁线圈上的电压电流波形进行监测,绘制了多脉冲励磁下磁环的磁化曲线,并结合含磁芯线圈动态电感量的递推公式计算出磁环在多脉冲励磁过程中磁导率的变化曲线;在高压三脉冲实验平台上对铁氧体磁芯和非晶磁芯实验感应腔进行了高压三脉冲实验,得到的磁芯多脉冲磁化规律与低压实验的结果一致。最后对两种磁环在多脉冲励磁下的磁性能差异进行了对比分析。 相似文献
11.
S. A. Novikov 《Optics and Spectroscopy》2002,92(1):9-12
The absolute values and the form of the cross section for two-photon one-electron excitation and ionization of the deep 2s shell of the Ar atom are calculated taking into account the many-body effects of relaxation of the atomic core in the fields of arising virtual vacancies and the decay of vacancies via the Auger and (or) radiative channels. The one-electron wave functions are calculated in the nonrelativistic approximation. The appearance of the Cooper minimum in the two-photon absorption cross section is established. The calculations are carried out for the linear and circular polarizations of photons of an incident laser beam. 相似文献
12.
The effects of electron exchange and spin orbit interaction in dissociative excitation processes in H2 molecules have been explored using excitation by polarized electrons. Observations of the circular and linear Stokes polarizations of the Balmer-alpha photons determined the alignment and orientation of the excited atomic hydrogen atoms, the excited molecular states, and the dissociative excitation processes via predissociation with short and long range transitions. 相似文献
13.
We study the single-vortex solution of the t-J model within resonating-valence-bond mean-field theory. We find two types of vortex cores, insulating and metallic, depending on the parameters of the model. The pairing order parameter near both cores have d(x(2)-y(2))+ietad(xy) symmetry. For some range of t/J the calculated tunneling spectrum of the metallic vortex core agrees qualitatively with the STM tunneling data for BSCCO. 相似文献
14.
We present an ultrafast route for a controlled, toggle switching of magnetic vortex cores with ultrashort unipolar magnetic field pulses. The switching process is found to be largely insensitive to extrinsic parameters, like sample size and shape, and it is faster than any field-driven magnetization reversal process previously known from micromagnetic theory. Micromagnetic simulations demonstrate that the vortex core reversal is mediated by a rapid sequence of vortex-antivortex pair creation and annihilation subprocesses. Specific combinations of field-pulse strength and duration are required to obtain a controlled vortex core reversal. The operational range of this reversal mechanism is summarized in a switching diagram for a 200 nm Permalloy disk. 相似文献
15.
Pan SH Hudson EW Gupta AK Ng K Eisaki H Uchida S Davis JC 《Physical review letters》2000,85(7):1536-1539
We report on low temperature scanning tunneling microscopy (STM) studies of the electronic structure of vortex cores in Bi 2Sr 2CaCu 2O (8+delta). At the vortex core center, an enhanced density of states is observed at energies near Omega = +/-7 meV. Spectroscopic imaging at these energies reveals an exponential decay of these "core states" with a decay length of 22+/-3 A. The fourfold symmetry sometimes predicted for d-wave vortices is not seen in spectroscopic vortex images. A locally nodeless order parameter induced by the magnetic field may be consistent with these measurements. 相似文献
16.
We show that, in the Thomas-Fermi regime, the cores of vortices in rotating dilute Bose-Einstein condensates adjust in radius as the rotation velocity, Omega, grows, thus precluding a phase transition associated with core overlap at high vortex density. In both a harmonic trap and a rotating hard-walled bucket, the core size approaches a limiting fraction of the intervortex spacing. At large rotation speeds, a system confined in a bucket develops, within Thomas-Fermi, a hole along the rotation axis, and eventually makes a transition to a giant vortex state with all the vorticity contained in the hole. 相似文献
17.
Zhiyong PangFei Yin Shaojie FangWenfeng Zheng Shenghao Han 《Journal of magnetism and magnetic materials》2012,324(5):884-888
Switching behaviors of magnetic vortex cores under external magnetic field in submicron circular permalloy disks have been systematically studied by using micromagnetic simulations. Simulation results show that the vortex core is stable in out-of-plane field even when it is located at the edge of the disk. The out-of-plane switching field Hsw is strongly dependent on the thickness of the disk. The core polarity and the vortex chirality can be modulated simultaneously on purpose by using a tilted field far smaller than the out-of-plane switching field Hsw. Moreover, it is found that the core polarities in asymmetric disks do not follow the direction of the z projection of the external saturation field. 相似文献
18.
The nonrelativistic absolute values and the form of the cross section for two-photon one-electron excitation and ionization of the 1s shell of the Ar atom are calculated in the second order of the quantum-mechanical perturbation theory by taking into account both the many-body effects of relaxation of the atomic core in the fields of arising virtual vacancies and the decay of vacancies via the autoionization Auger and (or) radiative channels. The appearance of the Cooper minimum in the two-photon absorption cross section is established. The calculations are carried out for the linear and circular polarizations of photons of an incident laser beam. The calculated results may be used for predictions. 相似文献
19.
A. Laforgia X. Leoncini L. Kuznetsov G.M. Zaslavsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):427-440
The advection of passive tracers in a system of 4 identical point vortices is studied when the motion of the vortices is chaotic.
The phenomenon of vortex-pairing has been observed and statistics of the pairing time is computed. The distribution exhibits
a power-law tail with exponent ∼ 3.6 implying finite average pairing time. This exponents is in agreement with its computed
analytical estimate of 3.5. Tracer motion is studied for a chosen initial condition of the vortex system. Accessible phase
space is investigated. The size of the cores around the vortices is well approximated by the minimum inter-vortex distance
and stickiness to these cores is observed. We investigate the origin of stickiness which we link to the phenomenon of vortex
pairing and jumps of tracers between cores. Motion within the core is considered and fluctuations are shown to scale with
tracer-vortex distance r as r
6. No outward or inward diffusion of tracers are observed. This investigation allows the separation of the accessible phase
space in four distinct regions, each with its own specific properties: the region within the cores, the reunion of the periphery
of all cores, the region where vortex motion is restricted and finally the far-field region. We speculate that the stickiness
to the cores induced by vortex-pairings influences the long-time behavior of tracers and their anomalous diffusion.
Received 28 September 2000 and Received in final form 9 February 2001 相似文献
20.
In a direct scanning tunneling spectroscopy experiment we address the problem of the quantum vortex phases in strongly confined superconductors. The strong confinement regime is achieved in in situ grown ultrathin single nanocrystals of Pb by tuning their lateral size to a few coherence lengths. Upon an external magnetic field, the scanning tunneling spectroscopy revealed novel ultradense arrangements of single Abrikosov vortices characterized by an intervortex distance up to 3 times shorter than the bulk critical one. At yet stronger confinement we discovered the giant vortex phase; the spatial evolution of the excitation tunneling spectra in the cores of these unusual quantum objects was explored. We anticipate the giant vortex phase to be a common feature of other confined quantum condensates such as superfluids, Bose-Einstein condensates of cold atoms, etc. 相似文献