共查询到20条相似文献，搜索用时 62 毫秒
1.
Krause S Berbil-Bautista L Herzog G Bode M Wiesendanger R 《Science (New York, N.Y.)》2007,317(5844):1537-1540
Switching the magnetization of a magnetic bit by injection of a spin-polarized current offers the possibility for the development of innovative high-density data storage technologies. We show how individual superparamagnetic iron nanoislands with typical sizes of 100 atoms can be addressed and locally switched using a magnetic scanning probe tip, thus demonstrating current-induced magnetization reversal across a vacuum barrier combined with the ultimate resolution of spin-polarized scanning tunneling microscopy. Our technique allows us to separate and quantify three fundamental contributions involved in magnetization switching (i.e., current-induced spin torque, heating the island by the tunneling current, and Oersted field effects), thereby providing an improved understanding of the switching mechanism. 相似文献
2.
We used a scanning tunneling microscope to probe the interactions between spins in individual atomic-scale magnetic structures. Linear chains of 1 to 10 manganese atoms were assembled one atom at a time on a thin insulating layer, and the spin excitation spectra of these structures were measured with inelastic electron tunneling spectroscopy. We observed excitations of the coupled atomic spins that can change both the total spin and its orientation. Comparison with a model spin-interaction Hamiltonian yielded the collective spin configuration and the strength of the coupling between the atomic spins. 相似文献
3.
We demonstrate the ability to measure the energy required to flip the spin of single adsorbed atoms. A low-temperature, high-magnetic field scanning tunneling microscope was used to measure the spin excitation spectra of individual manganese atoms adsorbed on Al2O3 islands on a NiAl surface. We find pronounced variations of the spin-flip spectra for manganese atoms in different local environments. 相似文献
4.
We studied the dynamics of a single cobalt (Co) atom during lateral manipulation on a copper (111) surface in a low-temperature scanning tunneling microscope. The Co binding site locations were revealed in a detailed image that resulted from lateral Co atom motion within the trapping potential of the scanning tip. Random telegraph noise, corresponding to the Co atom switching between hexagonal close-packed (hcp) and face-centered cubic (fcc) sites, was seen when the tip was used to try to position the Co atom over the higher energy hcp site. Varying the probe tip height modified the normal copper (111) potential landscape and allowed the residence time of the Co atom in these sites to be varied. At low tunneling voltages (less than approximately 5 millielectron volts), the transfer rate between sites was independent of tunneling voltage, current, and temperature. At higher voltages, the transfer rate exhibited a strong dependence on tunneling voltage, indicative of vibrational heating by inelastic electron scattering. 相似文献
5.
V Madhavan W Chen T Jamneala MF Crommie NS Wingreen 《Science (New York, N.Y.)》1998,280(5363):567-569
The Kondo effect arises from the quantum mechanical interplay between the electrons of a host metal and a magnetic impurity and is predicted to result in local charge and spin variations around the magnetic impurity. A cryogenic scanning tunneling microscope was used to spatially resolve the electronic properties of individual magnetic atoms displaying the Kondo effect. Spectroscopic measurements performed on individual cobalt atoms on the surface of gold show an energetically narrow feature that is identified as the Kondo resonance-the predicted response of a Kondo impurity. Unexpected structure in the Kondo resonance is shown to arise from quantum mechanical interference between the d orbital and conduction electron channels for an electron tunneling into a magnetic atom in a metallic host. 相似文献
6.
Wachowiak A Wiebe J Bode M Pietzsch O Morgenstern M Wiesendanger R 《Science (New York, N.Y.)》2002,298(5593):577-580
Thin film nanoscale elements with a curling magnetic structure (vortex) are a promising candidate for future nonvolatile data storage devices. Their properties are strongly influenced by the spin structure in the vortex core. We have used spin-polarized scanning tunneling microscopy on nanoscale iron islands to probe for the first time the internal spin structure of magnetic vortex cores. Using tips coated with a layer of antiferromagnetic chromium, we obtained images of the curling in-plane magnetization around and of the out-of-plane magnetization inside the core region. The experimental data are compared with micromagnetic simulations. The results confirm theoretical predictions that the size and the shape of the vortex core as well as its magnetic field dependence are governed by only two material parameters, the exchange stiffness and the saturation magnetization that determines the stray field energy. 相似文献
7.
Vibrational spectra for a single molecule adsorbed on a solid surface have been obtained with a scanning tunneling microscope (STM). Inelastic electron tunneling spectra for an isolated acetylene (C2H2) molecule adsorbed on the copper (100) surface showed an increase in the tunneling conductance at 358 millivolts, resulting from excitation of the C-H stretch mode. An isotopic shift to 266 millivolts was observed for deuterated acetylene (C2D2). Vibrational microscopy from spatial imaging of the inelastic tunneling channels yielded additional data to further distinguish and characterize the two isotopes. Single-molecule vibrational analysis should lead to better understanding and control of surface chemistry at the atomic level. 相似文献
8.
The bistability in the position of the two hydrogen atoms in the inner cavity of single free-base naphthalocyanine molecules constitutes a two-level system that was manipulated and probed by low-temperature scanning tunneling microscopy. When adsorbed on an ultrathin insulating film, the molecules can be switched in a controlled fashion between the two states by excitation induced by the inelastic tunneling current. The tautomerization reaction can be probed by resonant tunneling through the molecule and is expressed as considerable changes in the conductivity of the molecule. We also demonstrated a coupling of the switching process so that the charge injection in one molecule induced tautomerization in an adjacent molecule. 相似文献
9.
Control of magnetism on the atomic scale is becoming essential as data storage devices are miniaturized. We show that antiferromagnetic nanostructures, composed of just a few Fe atoms on a surface, exhibit two magnetic states, the Néel states, that are stable for hours at low temperature. For the smallest structures, we observed transitions between Néel states due to quantum tunneling of magnetization. We sensed the magnetic states of the designed structures using spin-polarized tunneling and switched between them electrically with nanosecond speed. Tailoring the properties of neighboring antiferromagnetic nanostructures enables a low-temperature demonstration of dense nonvolatile storage of information. 相似文献
10.
The miniaturization of magnetic devices toward the limit of single atoms calls for appropriate tools to study their magnetic properties. We demonstrate the ability to measure magnetization curves of individual magnetic atoms adsorbed on a nonmagnetic metallic substrate with use of a scanning tunneling microscope with a spin-polarized tip. We can map out low-energy magnetic interactions on the atomic scale as evidenced by the oscillating indirect exchange between a Co adatom and a nanowire on Pt(111). These results are important for the understanding of variations that are found in the magnetic properties of apparently identical adatoms because of different local environments. 相似文献
11.
Artificial nanostructures, each composed of a copper(II) phthalocyanine (CuPc) molecule bonded to two gold atomic chains with a controlled gap, were assembled on a NiAl(110) surface by manipulation of individual gold atoms and CuPc molecules with a scanning tunneling microscope. The electronic densities of states of these hybrid structures were measured by spatially resolved electronic spectroscopy and systematically tuned by varying the number of gold atoms in the chains one by one. The present approach provides structural images and electronic characterization of the metal-molecule-metal junction, thereby elucidating the nature of the contacts between the molecule and metal in this junction. 相似文献
12.
Single spins in solid-state systems are often considered prime candidates for the storage of quantum information, and their interaction with the environment the main limiting factor for the realization of such schemes. The lifetime of an excited spin state is a sensitive measure of this interaction, but extending the spatial resolution of spin relaxation measurements to the atomic scale has been a challenge. We show how a scanning tunneling microscope can measure electron spin relaxation times of individual atoms adsorbed on a surface using an all-electronic pump-probe measurement scheme. The spin relaxation times of individual Fe-Cu dimers were found to vary between 50 and 250 nanoseconds. Our method can in principle be generalized to monitor the temporal evolution of other dynamical systems. 相似文献
13.
Inelastic electron tunneling spectroscopy at low temperatures was used to investigate vibrations of Au(111) and Cu(111). The low-energy peaks at 9 millielectron volts (meV) on Au(111) and 21 meV on Cu(111) are attributed to phonons at surfaces. On Au(111), the phonon energy is not influenced by the different stacking of the surface atoms, but it is considerably influenced by different atomic distances within the surface layer. The spatial variation of the phonon excitation is measured in inelastic electron tunneling maps on Au(111), which display atomic resolution. This atomic resolution is explained in terms of site-specific phonon excitation probabilities. 相似文献
14.
An experimental method based on the Landau-Zener model was developed to measure very small tunnel splittings in molecular clusters of eight iron atoms, which at low temperature behave like a nanomagnet with a spin ground state of S = 10. The observed oscillations of the tunnel splittings as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum interference of two tunnel paths of opposite windings. Transitions between quantum numbers M = -S and (S - n), with n even or odd, revealed a parity effect that is analogous to the suppression of tunneling predicted for half-integer spins. This observation is direct evidence of the topological part of the quantum spin phase (Berry phase) in a magnetic system. 相似文献
15.
Miller WH 《Science (New York, N.Y.)》1986,233(4760):171-177
16.
Rosei F Schunack M Jiang P Gourdon A Laegsgaard E Stensgaard I Joachim C Besenbacher F 《Science (New York, N.Y.)》2002,296(5566):328-331
The electronic connection of single molecules to nanoelectrodes on a surface is a basic, unsolved problem in the emerging field of molecular nanoelectronics. By means of variable temperature scanning tunneling microscopy, we show that an organic molecule (C90H98), known as the Lander, can cause the rearrangement of atoms on a Cu(110) surface. These molecules act as templates accommodating metal atoms at the step edges of the copper substrate, forming metallic nanostructures (0.75 nanometers wide and 1.85 nanometers long) that are adapted to the dimensions of the molecule. 相似文献
17.
The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and "conducting wires" in a very flexible and convenient manner. 相似文献
18.
An electrodeposition technique is described that produces atomically flat epitaxial metal overlayers of quality similar to that obtained by ultrahigh vacuum techniques at elevated temperature. In this approach, a metal of interest such as silver is co-deposited with a reversibly deposited mediator metal. The mediator is periodically deposited and stripped from the surface, and this serves to significantly increase the density of two-dimensional islands of silver atoms, promoting a layer-by-layer thin-film growth mode. In situ scanning tunneling microscopy was used to demonstrate the growth process for the heteroepitaxial system silver/gold (111) with either lead or copper as the mediator. 相似文献
19.
Zhao A Li Q Chen L Xiang H Wang W Pan S Wang B Xiao X Yang J Hou JG Zhu Q 《Science (New York, N.Y.)》2005,309(5740):1542-1544
We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au111 surface exhibited no Kondo effect. Cutting away eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level. 相似文献
20.
As electrons are injected at various energies into ferromagnetic material with their spin polarization vector perpendicular to the axis of the magnetization, we observe precessional motion of the spin polarization on the femtosecond time scale. Because of angular momentum conservation, the magnetization vector must precess as well. We show that spin injection will generate the precessional magnetization reversal in nanosized ferromagnetic bits. At reasonable injected current densities this occurs on the picosecond time scale. 相似文献