We fabricate magnetic nanojunctions using Ni 78 Fe 22 (Py) thin-film edges which sandwich the high-mobility molecules, 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and investigate spin transport properties. As a result, a clear positive magnetoresistance (MR) effect is observed in Py/C8-BTBT/Py nanojunctions at room temperature. In addition, the observed positive MR effect can reveal that the magnetization curves of the thin-film edges are different from those of the thin film measured by magneto-optic Kerr effect spectroscopy. These findings offer a new insight into high-mobility molecular nano-spintronics, leading to the creation of functional spin devices.
We have studied the surface morphologies and magnetic properties of Fe and Co thin films evaporated on polyethylene naphthalate (PEN) organic substrates toward the fabrication of spin quantum cross devices. As a result, the surface roughnesses of Co (6.1 nm)/PEN and Co (12 nm)/PEN are as small as 0.1 and 0.09 nm, respectively, corresponding to less than one atomic layer, in the same scanning scale as the thickness. As for the magnetic properties, the coercive force of the Co/PEN shows the constant value of 2 kA/m upon decreasing the Co thickness from 35 to 10 nm, and it increases up to 7 kA/m upon decreasing the Co thickness from 10 to 5 nm. It decreases when the Co thickness is less than 5 nm. These results can be explained by the competition between the shape magnetic anisotropy and the induced magnetic anisotropy.
The frequency dependences of the magnetoimpedance for tunneling junctions Al/Al2O3/Al and that for coercive differential spin tunneling junctions Co/Al2O3/Co fabricated onto glass substrates by ion-beam mask sputtering are investigated and the feasibility of application is discussed. The RF impedance of the tunneling junctions can be understood by the parallel current model of the tunneling and the displacement current. The imaginary part of the impedance of the spin tunneling junction changes in an external magnetic field due to the magnetoresistance effect. The magnetoimpedance ratio is estimated to decrease at high frequencies. Spin tunneling junctions having low resistivity and a low dielectric constant are required in order to obtain high-frequency response. Detection of the imaginary part of the impedance for magnetic sensing may be desirable, because the imaginary part of the magnetoimpedance effect is estimated to be larger than the real part.
Fabricating nanoscale patterns with sub-10 nm feature size has been an important research target for potential applications in next-generation memories, microprocessors, logic circuits and other novel functional devices. Typically, according to the International Technology Roadmap for Semiconductor (ITRS) from 2009, an 8.9 nm node device is targeted for the year 2024. To achieve this milestone, liquid immersion lithography and extreme ultraviolet (EUV) lithography can be expected to be among the most commonly used techniques for the fabrication of nanopatterns. With liquid immersion lithography using a wavelength of 193 nm and a high numerical aperture (NA), it has been demonstrated that 32 nm features can be patterned (Finders et al., 2008; Sewell et al., 2009). EUV lithography using a short wavelength of 13.5 nm and 0.3-NA exposure tool has also enabled the printing of 22 nm half-pitch lines (Naulleau et al., 2009). On the other hand, attractive patterning techniques, such as a superlattice nanowire pattern transfer (SNAP) method (Melosh et al., 2003; Green et al., 2007), a mold-to-mold cross imprint (MTMCI) process (Kwon et al., 2005) and a surface sol-gel process combined with photolithography (Fujikawa et al., 2006), are currently proposed and pursued actively. The SNAP method, which is based on translating thin film growth thickness control into planar wire arrays, has enabled the production of molecular memories consisting of 16 nm wide titanium/silicon nanowires. The MTMCI process using silicon nanowires formed by spacer lithography, in which nanoscale line features are defined by the residual part of a conformal film on the edges of a support structure with the linewidth controlled by the film thickness, has been used to produce a large array of 30 nm wide silicon nanopillars. With the surface sol-gel process combined with photolithography, where the linewidth is determined by the thickness of coating silica layer on the resist pattern, the size reduction and the large area of sub-20 nm silica walls have been achieved. Recently, we have proposed a double nano-baumkuchen (DNB) structure, in which two thin slices of alternating metal/insulator nano-baumkuchen are attached so that the metal/insulator stripes cross each other, as part of a lithography-free nanostructure fabrication technology (Ishibashi, 2003 & 2004; Kaiju et al., 2008; Kondo et al., 2008). The schematic illustration of the fabrication procedure is shown in Fig. 1. First, the metal/insulator spiral heterostructure is fabricated using a vacuum evaporator including a film-rolled-up system. Then, two thin slices of the metal/insulator nano-baumkuchen
We investigate the laser wavelength dependence of structural and magnetic transitions on the surface of an iron–aluminum (FeAl) alloy induced by nanosecond pulsed laser irradiation. The formation of self-organized FeAl stripes with a wavelength-dependent period is observed in a local area on the (111)-oriented plane. Focused magneto-optical Kerr effect measurements reveal that the coercivity reaches up to 1.2 kOe with increasing the magnetic field rotation angle, which is estimated from the stripe direction, in FeAl stripes irradiated at 355 nm, and its magnetization reversal can be explained by the domain-wall motion model. On the other hand, the magnetization reversal agrees with the Stoner–Wohlfarth model in FeAl stripes irradiated at 1064 nm. This magnetic transition originates from the B2-to-A2 phase transition in stripe structures and bulk regions. These results indicate that the magnetic transition from the incoherent to coherent mode as well as the structural transformation of stripe patterns can be controlled by the incident laser wavelength.
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