The transmission and reflection spectra of arrays of heterogeneous nanowires made of Ni/Co, FeNi/Co, and Ni/Fe, formed in track polymer membranes by the galvanic method, have been studied in the frequency range from 16 to 250 THz. Many peaks in the 16-20 THz range were found in the transmission spectra, while they are not observed in the spectrum of a track membrane without nanowires. The absorption spectra of an array of nanowires in a track membrane and a membrane without wires are calculated from the obtained spectra. It was found that the fraction of the THz radiation power absorbed by nanowires and its spectrum depend on the materials of the nanowires. The features of the observed spectra can be explained by two mechanisms. The first is the inverse laser effect in magnetic nanocontacts. And the second is the change in electrical resistance due to spin-flip transitions between the spin subbands in the case of a non-coplanar distribution of the magnetization of the magnetic layers. This class of quasi-one-dimensional structures looks promising for creating THz radiation detectors in a wide spectral range and at room temperature.
By means of magnetoresistance and magnetic force microscopy (MFM) measurements the electrical and magnetic
properties of ferromagnetic strips and crosses of hybrid nanostructures Py/Mo (Py - permalloy (Ni 80 Fe 20), Mo - molybdenum) have been investigated. Unusual behaviour of the cross magnetoresistance in these nanostructures was
found. The dependences of the cross resistance against external magnetic field have the image of the curves with
hysteresis typical for anisotropic magnetoresistance (AMR). However, they demonstrate anomalous magnetoresistance
dependence on orientation relatively to the axis of the ferromagnetic arm of the cross. In the transverse magnetic field
(perpendicular to the axis of the ferromagnetic arm) magnetoresistance has two minima as for the longitudinal AMR. In
the longitudinal magnetic field (parallel to the axis of ferromagnetic arm) there are two maxima, typical for the
transverse AMR. The value of the effect is about one percent. The AMR of the strip has the supplementary extremes,
indicated on a more complex character of magnetization reversal, depended on the shape of nanostructures. The data of
the magnetoresistance measurements are compared with MFM images.
Iron film growth conditions and films properties on A- and R- sapphire surfaces were investigated. The best growth
conditions were achieved at temperatures about 250 - 300°C. A 10 nm Mo seed layer on the A-sapphire surface
improves Fe film morphology and film roughness becomes less than 1 nm. As a result epitaxial Fe (011) films with
high residual electron mean free paths (about 0.5 mkm) were grown on the A-sapphire surface. These films can be
used for ballistic ferromagnetic planar nanostructures fabrication.
The magnetic domain configuration of epitaxial iron nanostructures shaped as bridges and crosses depending on the
orientation relative to the easy magnetic axis Fe [100] was examined. If the long side of the bridge is directed along
the easy magnetic axis, the single domain structure state is easily reached up to maximum structure width about 2
mkm. A stripe domain structure can be observed when the easy magnetic axis is normal to the long rectangular
structure axis. The structure orientation at some angle with the easy magnetic axis leads to a magnetic domain
configuration along the easy axis is independent of the structure size down to a structure width ~0.5 mkm and
depends only on the easy axis direction. The single domain state can be obtained in structures with a width less than
0.5 mkm. The cross-type structures may have only a two-fold symmetry magnetic configuration. Trapeziform
domains were found in structures directed along the hard Fe magnetic axis.
A road map for the fabrication of epitaxial metallic electrodes, quantum dots and wires is considered for potential application in solid-state qubit technology. The nanotechnology developed includes high quality low-roughness film epitaxy, probe lithography and subtractive techniques for the fabrication of epitaxial nanostructures with a lateral resolution down to 10 nm.
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