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Arrays of planar symmetric gold quadrumers consisting of a central nano-disc surrounded by three similar nano-discs belonging to the D(3h) point group were designed and fabricated. Since the geometrical configuration of quadrumers is the same as planar trigonal molecules, nano-discs can play the roles of artificial atoms to study the coupling trends among them. The plasmonic properties of the nano-disc structures are investigated by reflection spectrum measurement and finite-difference time-domain calculation with good agreement. Plasmon interaction among the nano-discs is also studied via a mass-spring coupled oscillator model. A pronounced Fano resonance (FR) is observed for the fabricated nano-discs with inter-disk gaps of around 18 nm during light irradiation at normal incidence. Although the obtained FR is independent of the excitation polarization, the near-field energy spatial distribution can be flexibly tuned by the polarization direction. This has potential applications in nano-lithography, optical switching and nonlinear spectroscopy.

Excellent tunnel magneto resistance (TMR

Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-disk position to study the effect of symmetry breaking in pentamers. It is found that while planar symmetric oligomers can exhibit a single Fano Resonance (FR), an offset of the central nano-disk at a controlled gap of 3 nm from the nearest neighbor nano-disk, gives rise to the appearance of an additional dark mode that can potentially be used in localized surface plasmon resonance sensing. It is shown that this mode leads to the appearance of the second FR in the same spectrum. The simulation results are in a good agreement with experimental data. Furthermore, it is found that unique near-field energy distribution in the asymmetric pentamers can be well tuned to be localized at one, two or three of the four subwavelength gaps of the pentamer selectively by only changing the polarization orientation of a single light source.

Arrays of planar symmetric coupled oligomers support higher sensitivity optical response than uncoupled plasmonic systems. In this work, the transition from isolated to collective optical modes in plasmonic oligomers, such as pentamers and quadrumers, is investigated via experimental characterization and simulation with good agreement. The designed and fabricated metallic oligomers consist of a single central disk and outer ring-like disks in nanoscales. It is shown that while the far-field spectral responses of oligomers are polarization-independent, due to the structure symmetry, the spatial localization of near-field energy in nanogaps can be polarization-controlled. This localization is established at a normal-incident light of a single source rather than co-illumination by two light sources accompanied by different incident angles or phase shift. It can overcome the spatial restrictions of conventional optics. The influence of the nano-disk sizes and gaps among them on the intensity and shape of the localized near-field energy in pentamers and quadrumers is also studied.

A novel multi-bit dual pseudo spin valve with perpendicular magnetic anisotropy is investigated for spin transfer torque (STT) switching. The structure consists of two free layers and one reference layer, and all are based on Co/Pd multilayer. STT switching of the multi-bit device shows distinct four resistance levels. The selection of intrinsic properties of each ferromagnetic layer can be controlled for distinct separation of the resistance levels as well as the respective STT switching current. Reversible transitions between different states can be achieved by a pulsed current, in which its critical value is found to be linearly dependent on pulse duration.

No abstract

We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4nm/Pd t] 6 (t = 1.0-2.0 nm) multilayers fabricated by DC sputtering in a ultrahigh vacuum chamber. Saturation magnetization, M s , and uniaxial anisotropy, K u , of the multilayers decrease with increasing the spacing thickness, with a M s of 155 emu/cc and a K u of 1.14×10 5 J/m 3 at a spacing thickness of t = 2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe film decrease as function of Pd thickness, indicating the major contribution of surface/interfacial magnetism to the magnetic properties of the film.