992 research outputs found
Nutation versus angular dependent NQR spectroscopy and the impact of underdoping on charge inhomogeneities in YBaCuO
We describe two different nuclear quadrupole resonance (NQR) based
techniques, designed to measure the local asymmetry of the internal electric
field gradient, and the tilt angle of the main NQR principal axis z from the
crystallographic axis c. These techniques use the dependence of the NQR signal
on the duration of the radio frequency (rf) pulse and on the direction of the
rf field H1 with respect to the crystal axis. The techniques are applied to
oriented powder of YBaCuO fully enriched with 63Cu.
Measurements were performed at different frequencies, corresponding to
different in-plane copper sites with respect to the dopant. Combining the
results from both techniques, we conclude that oxygen deficiency in the chain
layer lead to a rotation of the NQR main principal axis at the nearby Cu on the
CuO2 planes by 20+-degrees. This occurs with no change to the asymmetry. The
axis rotation associated with oxygen deficiency means that there must be
electric field inhomogeneities in the CuO2 planes only in the vicinity of the
missing oxygen.Comment: 9 pages, 10 figure
Ultranarrow conducting channels defined in GaAs-AlGaAs by low-energy ion damage
We have laterally patterned the narrowest conducting wires of two-dimensional electron gas (2DEG) material reported to date. The depletion induced by low-energy ion etching of GaAs-AlGaAs 2DEG structures was used to define narrow conducting channels. We employed high voltage electron beam lithography to create a range of channel geometries with widths as small as 75 nm. Using ion beam assisted etching by Cl2 gas and Ar ions with energies as low as 150 eV, conducting channels were defined by etching only through the thin GaAs cap layer. This slight etching is sufficient to entirely deplete the underlying material without necessitating exposure of the sidewalls that results in long lateral depletion lengths. At 4.2 K, without illumination, our narrowest wires retain a carrier density and mobility at least as high as that of the bulk 2DEG and exhibit quantized Hall effects. Aharonov–Bohm oscillations are seen in rings defined by this controlled etch-damage patterning. This patterning technique holds promise for creating one-dimensional conducting wires of even smaller sizes
Non-Volatile Memory Characteristics of Submicrometre Hall Structures Fabricated in Epitaxial Ferromagnetic MnAl Films on GaAs
Hall-effect structures with submicrometre linewidths (<0.3pm) have been fabricated in ferromagnetic thin films of Mn[sub 0.60]Al[sub 0.40] which are epitaxially grown on a GaAs substrate. The MnAl thin films exhibit a perpendicular remanent magnetisation and an extraordinary Hall effect with square hysteretic behaviour. The presence of two distinct stable readout states demonstrates the potential of using ultrasmall ferromagnetic volumes for electrically addressable, nonvolatile storage of digital information
Epitaxial-tau(Mn,Ni)Al/(Al,Ga)As heterostructures: Magnetic and magneto-optic properties
Ferromagnetic Perpendicularly magnetized epitaxial thin films of tau (Mn,Ni)AI have been successfully grown on AlAs/GaAs heterostructures by molecular beam epitaxy. We have investigated the polar Kerr rotation and magnetization of tau MnAl and (Mn,Ni) Al as a function of Mn and Ni concentration. The largest polar Kerr rotation and remnant magnetization were obtained for Mn0.5Al0.5 thin films with values of 0.16-degrees and 224 emu/cm3, respectively. We observed that the Kerr rotation and magnetization remained constant with Ni additions up to about 12 at. % and subsequently decreased with further Ni additions. We discuss these results and one possible method of enhancing the Kerr rotation
The extraordinary Hall effect in coherent epitaxial tau (Mn,Ni)Al thin films on GaAs
Ultrathin coherent epitaxial films of ferromagnetic tau(Mn,Ni)0.60Al0.40 have been grown by molecular beam epitaxy on GaAs substrates. X-ray scattering and cross-sectional transmission electron microscopy measurements confirm that the c axis of the tetragonal tau unit cell is aligned normal to the (001) GaAs substrate. Measurements of the extraordinary Hall effect (EHE) show that the films are perpendicularly magnetized, exhibiting EHE resistivities saturating in the range of 3.3-7.1 muOMEGA-cm at room temperature. These values of EHE resistivity correspond to signals as large as +7 and -7 mV for the two magnetic states of the film with a measurement current of 1 mA. Switching between the two magnetic states is found to occur at distinct field values that depend on the previously applied maximum field. These observations suggest that the films are magnetically uniform. As such, tau(Mn,Ni)Al films may be an excellent medium for high-density storage of binary information
On some pelagic Doliolid tunicates (Traliacea, Doliolida) collected by a submersible off the eastern NorthAmerican coast
Specimens of Doliolids collected from a submersible at several stations off the eastern coast of North America were examined. Four species were identified, of which three were described by Godeaux (1996). Of these, one belongs to the new genus, Paradoliopsis (Godeaux, 1996). It is proposed that the order Doliolida be divided into two suborders: the Doliolidina (animals with eight muscle bands), and the Doliopsidina (animals with five muscle bands). Each suborder is represented in our collection by two families. For the Doliolidina these families are the Doliolidae (Doliolinetta intermedia) and the Doliopsoididae (Doliopsoides atlantician), and for the Doliopsidina. the families are the Doliopsidae (Doliopsis bahamensis) and the Paradoliopsidae (Paradoliopsis harbisoni)
On some pelagic Doliolid tunicates (Traliacea, Doliolida) collected by a submersible off the eastern NorthAmerican coast
peer reviewedSpecimens of Doliolids collected from a submersible at several stations off the eastern coast of North America were examined. Four species were identified, of which three were described by Godeaux (1996). Of these, one belongs to the new genus, Paradoliopsis (Godeaux, 1996). It is proposed that the order Doliolida be divided into two suborders: the Doliolidina (animals with eight muscle bands), and the Doliopsidina (animals with five muscle bands). Each suborder is represented in our collection by two families. For the Doliolidina these families are the Doliolidae (Doliolinetta intermedia) and the Doliopsoididae (Doliopsoides atlantician), and for the Doliopsidina. the families are the Doliopsidae (Doliopsis bahamensis) and the Paradoliopsidae (Paradoliopsis harbisoni)
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