Development of spin-polarized scanning tunnel microscopy/spectroscopy (SP-STM/STS) is reviewed and the working principle of SP-STM/STS is discussed with paying special attention to the obtention of the spin-resolved local density of states (LDOS). We discuss the case of bct-Mn epitaxial films grown on Fe(001) whisker. The bct-Mn(001) layers couple antiferromagnetically with the adjacent layers and there is a spin-dependent LDOS peak above the Fermi level, to which highly-polarized two dz2 surface states contribute. The highest lateral magnetic resolution obtained in this system is 0.4 nm. Performing a detailed analysis of the SP-STS measurements, we conclude that the bct-Mn(001) surface has a 60±16% polarization at the energy position of the spin-dependent LDOS peak.
Formation process of ferromagnetic nanodot arrays on a periodically nanopatterned Cu(001) surface with nitrogen atoms are overviewed, and their magnetic properties studied by surface magneto-optical Kerr effect (SMOKE) in ultra high vacuum are described. The square lattice nanopattern induced by the strain due to nitrogen adsorption is formed by the strain-relief mechanism of the Cu lattice near the surface. On top of that, the diffusion and the adsorption of the deposited atoms depend on the substrate lattice strain, and the ferromagnetic metal island preferentially grow at the less strained clean Cu surface. As a result, a square nanodot array of 7 nm × 7 nm is formed on the surface. The hysteresis loops of the arrays were in-situ measured by SMOKE between 400 K and 95 K. The results indicate long range ferromagnetic order is established among the superparamagnetic Co dots of two-monoatomic-layers high by the magnetic interaction through the monolayer Co strips.
The photoemission electron microscopy using synchrotron radiation (SR-PEEM) combined with the X-ray circular and linear dichroism (XMCD and XMLD) is one of the most powerful techniques to investigate the magnetic domain structure of micro magnetic materials or surfaces and interfaces of magnetic thin films. With the method, we can observe the magnetic domain structure directly to a very high spatial resolution. In this paper, the technique of SR-PEEM for the observation of the magnetic domain structure and its applications to the Ni-micro ring, and the ferromagnetic/antiferromagnetic interface, i.e. the Fe wedge/NiO(001), are introduced.
We investigate the nano-physics of atom bridges made from magnetic atoms formed between a Scanning Tunneling Microscope-tip (STM-tip) and a solid surface within the density functional theory. We consider a twisted ladder structure to represent the atom bridge. In the case of an Fe atom bridge, we find that the magnetic and transport properties depend on the distance between the nearest neighbor atoms along the bridge axis. We consider the alloy atom bridges whose components are found on both the right and left hand side of the Pauling-Slater curves, and show their corresponding magnetic and transport properties. On the basis of our numerical results, we discuss the origin of these interesting properties and the possibility for designing the properties of the atom bridge by STM-tip manipulation and/or alloying.
We report on the recent progress of our study concerning the spin-polarized scanning tunneling spectroscopy (SP-STS). The magnetic states of Fe nano-magnets on W(001) substrates have been investigated. We have observed single-domain and vortex states in the nano-magnets. The micromagnetic simulation well reproduces the magnetic contrast observed in a nano-magnet and demonstrates that the contrast originates from the vortex state in the ground state. The high-resolution magnetic images enable us to experimentally determine the boundary between the single-domain and vortex states. The boundary directly observed with SP-STS is consistent with theoretical predictions. SP-STM with an AC magnetic field for Mn/Fe(001) performed by Wulfhekel et al. is also introduced, indicating that a 180-degree domain wall is formed in the frustrated region in the anti-ferromagnetically coupled Mn layers. Furthermore, the expansion of the domain wall width in the region with increasing the Mn thickness has been obviously observed. Finally, we touch on potentials and remaining issues for industrial application of SP-STS/STM.
Our recent experimental results on the surface magnetic structures of Cr(001) films epitaxially grown on Au(001) surface were reviewed. Magnetic imaging of the Cr(001) films was performed at room temperature by spin-polarized scanning tunneling spectroscopy. It is found that two-step growth of Cr layers at two different growth temperatures results in a chemically clean and atomically flat surface. We observed distinct magnetic contrasts by using differential conductivity maps with Fe-coated W tips. The results are consistent with the topological antiferromagnetic (AF) order in the Cr(001) film surface. In addition, the existence of domains with different quantization axes of AF order and the narrow domain-wall width (∼6 nm) near screw dislocations were found. The quantization axis of each domain is obviously correlated with the step direction. The screw-dislocation distance may play an important role in determining the domain wall width. These experimental results are subject to high-density steps and screw dislocations.
Antiferromagnetism of stacked nanographite is investigated using the Hubbard-type model. We find that the open shell electronic structure can be an origin of the decreasing magnetic moment with decreasing inter-layer distance, as experiments of adsorption of molecules suggest. Next, possible charge-separated states are considered using the extended Hubbard model with nearest-neighbor repulsive interactions. The charge-polarized state could appear, when a static electric field is present in the graphene plane for example. Finally, superperiodic patterns with a long distance in a nanographene sheet observed by STM are discussed in terms of the interference of electronic wave functions with a static linear potential theoretically. In the analysis by the k • p model, the oscillation period decreases spatially in agreement with experiments.
The mass spectrometry is one of the most powerful characterization methods in materials processing technologies. RBS and SIMS have been used extensively for the determination of stoichiometry and impurity distributions of materials. Even if the sensitivity is low, RBS provides accurate identification of the atomic masses and surface depth profiling of the elements. On the contrary, SIMS is very sensitive although the quantitative determination of the composition and local order structure of the material surface is difficult. On the basis of these characteristics, RBS is thought to be the absolute measurement technique, and SIMS the relative measurement technique. The material characteristics can be analogized from material elements, that are determined by the absolute and relative measurement technique.