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Rolled-up Au/Co/Au microtubes with up to three windings were fabricated by the combination of strain engineering, conventional photolithography, and electron beam deposition. First, magnetization properties of the initial 2D film arrays and the corresponding tube arrays were studied and strong influences of magnetostrictive and shape anisotropy are observed. Second, the mechanical deformation was examined by an instrumented indentation technique at the nanoscale and analyzed by contact mechanics theory. The loading curve fitting in the elastic regime by the Hertz model provides a first approximation of the nanomembrane radial elastic modulus of about 135 GPa. [ABSTRACT FROM AUTHOR]

The metal-to-insulator (MI) transition of a V2O3 thin film is studied, using a surface acoustic wave delay line. The V2O3 film covers not only the sound path but also one of the interdigital transducers (IDTs). The resulting mismatch of the IDTs detunes the delay line, until the film passes through the MI transition. This “self-retuning” behavior makes the device extremely sensitive to the initial changes of the electrical and dielectric properties of the film during the MI transition. Attenuation and sound velocity are measured between 260 and 4.2 K. Both suggest a precursor to the MI transition in the paramagnetic metallic regime. The existence of a precursor is consistent with recent extended x-ray absorption fine structure measurements. An oscillatory behavior with steep reductions of the sound velocity is observed during the MI transition. The reductions of the sound velocity probably indicate the recently predicted anomaly at the Mott transition. [ABSTRACT FROM AUTHOR]

We show an efficient way to investigate the magnetic behavior of nanotube stubs based on the embedding of aligned iron-filled carbon nanotubes in silicon oxide using thermal chemical vapor deposition and gradual mechanical polishing afterwards. On the one hand, during the covering process the saturation magnetization moment rises due to the transformation of Fe3C into body-centered-cubic-Fe and graphite. On the other hand, the coercivity drops, mainly induced by changes in the shape of the nanowires. Further magnetization measurements of the embedded sample point to most of the ferromagnetic nanowires being located near the surface of the substrate. The coercivity increases when reducing the thickness of the nanotube array. The anomalous high coercivity of the Fe nanowires encapsulated by non magnetic carbon nanotubes make them suitable for high density data storage applications. [ABSTRACT FROM AUTHOR]

We have performed morphological analysis of samples of Fe nanowires encapsulated into aligned multiwalled carbon nanotubes (Fe-MWCNTs) via 57Fe Mössbauer spectroscopy. The aligned Fe-MWCNTs were obtained by pyrolysis of ferrocene onto an oxidized Si substrate. Transmission Mössbauer spectroscopy (TMS) and backscattered conversion electron Mössbauer spectroscopy (CEMS) were applied in order to distinguish different Fe phases and their spatial distribution within the whole sample and along the tubes’ height. A characterization (on a large spatial scale) of the aligned CNT samples was performed by obtaining TMS spectra for selected spots positioned at different locations of the sample. While the total Fe content changes considerably from one location to another, the γ-Fe/α-Fe phase ratio is constant onto a relatively large area. Using TMS and CEMS for all aligned Fe-MWCNT samples it is also shown that along the CNT axes, going to the top of the nanotube the relative content of the γ-Fe phase increases. Going to the opposite direction, i.e., towards the silicon substrate, the relative content of the Fe3C phase increases, which is in agreement with our previous works. The results of an additional Mössbauer spectroscopy experiment in TMS and CEMS modes performed on a nonaligned sample support the conclusion that in our case the iron phases in the channels of carbon nanotubes are spatially separated as individual nanoparticles. The relative intensity ratio of the α-Fe phase Mössbauer sextets shows good magnetic texture along the nanotubes’ axis for one of the aligned samples and the lack of such orientation for the others. [ABSTRACT FROM AUTHOR]

We report on exchange-induced spin polarization in the magnetic semiconductor EuS at room temperature studied by x-ray magnetic-circular-dichroism measurements. This turns EuS into a promising material for spin-injection applications. The system investigated is a Co/EuS multilayer grown on top of a Co/Pt multilayer on a Si(111) substrate. The EuS moments are aligned antiparallel to the Co moments in a narrow region at the Co/EuS interface. We attribute this exchange-induced alignment to a magnetic proximity effect which is closely related to the magnetic exciton originally proposed by Kasuya [IBM J. Res. Dev.14, 214 (1970)] to explain ferromagnetism in EuS. [ABSTRACT FROM AUTHOR]

Using surface acoustic waves, the elastomagnetic coupling could be studied in thin single-crystalline plates of the ferrimagnetic semiconductor FeCr2S4 by measuring the attenuation and the frequency tracking in the temperature range of 4.2–200 K. The data clearly display the anomalies found in low-field magnetization measurements. [ABSTRACT FROM AUTHOR]

Thin V2O3 films were deposited on a piezoelectric substrate by electron-beam evaporation. Surface acoustic waves were generated by interdigital transducers. The attenuation and sound velocity were investigated from 260 to 10 K, providing an insight into the temperature-dependent electrical, dielectrical, and elastic properties of V2O3 at the metal-to-insulator transition. [ABSTRACT FROM AUTHOR]

Provides information on a study that proposed a method to deduce energy distribution of defects in the band gap of a semiconductor by measuring the complex admittance of a junction. Theory for the determination of an energy distribution of defects from junction admittance data; Modeling of the junction capacitance and determination of defect distributions; Application to admittance measurements on thin film solar cells; Conclusions.

MnSi films are grown by evaporation of Mn onto Si(111) substrates under ultrahigh-vacuum conditions. Films are characterized with real- and reciprocal-space surface-science techniques such as scanning tunneling microscopy and low-energy electron diffraction. The bulk structure is determined ex situ by transmission electron microscopy (TEM). Thin (<60 Å Mn-deposited) MnSi films show a regularly modulated surface due to a 3% lattice mismatch of the interfaces. TEM confirms epitaxial growth and demonstrates smooth, atomically flat interfaces. Temperature-dependent ex situ measurements of the magneto-optic Kerr effect show ferromagnetism with an in-plane easy axis magnetic anisotropy for 60- and 100-Å-thick Mn films. [ABSTRACT FROM AUTHOR]

The semiconducting character and the large spin moment of 7/2 μB of europium sulfite are important preconditions for applications in the field of spintronics. However, the low Curie temperature (TC=16.5 K) excludes EuS from commercial application. We have studied a variety of Co/EuS multilayer samples deposited in a molecular beam epitaxy system with varying numbers of layers and different single-layer thickness. Magneto-optic Kerr effect measurements at low temperatures (10 K) indicate an antiferromagnetic coupling between EuS and Co moments. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work we investigate quantum transport in Cu nanowires created by bringing macroscopic Cu wires into and out of contact under an applied magnetic field in air. Here we show that a 70% magnetoconductance effect can be seen in a Cu nanowire in a field of 2 mT at room temperature. We propose that this phenomenon is a consequence of spin filtering due to the adsorption of atmospheric oxygen modifying the electronic band structure and introducing spin split conduction channels. Since bulk Cu is not magnetic it may provide a new perspective for spintronics. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the quantum transport behavior of Cu nanowires created by bringing two macroscopic Cu wires into and out of contact at room temperature. We have observed quantum conductance with steps of both e[SUP2]/h and 2e[SUP2]/h. We conclude that the spin degeneracy can be broken in nonmagnetic Cu nanowires. [ABSTRACT FROM AUTHOR]