1,231 research outputs found
Magnetic nanostructures by adaptive twinning in strained epitaxial films
We exploit the intrinsic structural instability of the Fe70Pd30 magnetic
shape memory alloy to obtain functional epitaxial films exhibiting a
self-organized nanostructure. We demonstrate that coherent epitaxial straining
by 54% is possible. The combination of thin film experiments and large-scale
first-principles calculations enables us to establish a lattice relaxation
mechanism, which is not expected for stable materials. We identify a low twin
boundary energy compared to a high elastic energy as key prerequisite for the
adaptive nanotwinning. Our approach is versatile as it allows to control both,
nanostructure and intrinsic properties for ferromagnetic, ferroelastic and
ferroelectric materials.Comment: Final version. Supplementary information available on request or at
the publisher's websit
Scaling Study and Thermodynamic Properties of the cubic Helimagnet FeGe
The critical behavior of the cubic helimagnet FeGe was obtained from
isothermal magnetization data in very close vicinity of the ordering
temperature. A thorough and consistent scaling analysis of these data revealed
the critical exponents , , and . The
anomaly in the specific heat associated with the magnetic ordering can be well
described by the critical exponent . The values of these
exponents corroborate that the magnetic phase transition in FeGe belongs to the
isotropic 3D-Heisenberg universality class. The specific heat data are well
described by ab initio phonon calculations and confirm the localized character
of the magnetic moments.Comment: 10 pages, 8 figure
Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh
Based on ab initio total energy calculations we show that two magnetic states
of rhodium atoms together with competing ferromagnetic and antiferromagnetic
exchange interactions are responsible for a temperature induced metamagnetic
phase transition, which experimentally is observed for stoichiometric
alpha-FeRh. A first-principle spin-based model allows to reproduce this
first-order metamagnetic transition by means of Monte Carlo simulations.
Further inclusion of spacial variation of exchange parameters leads to a
realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.
Pressure Induced Topological Phase Transitions in Membranes
Some highly unusual features of a lipid-water liquid crystal are revealed by
high pressure x-ray diffraction, light scattering and dilatometric studies of
the lamellar (bilayer ) to nonlamellar inverse hexagonal ()
phase transition. (i) The size of the unit cell of the phase increases
with increasing pressure. (ii) The transition volume, ,
decreases and appears to vanish as the pressure is increased. (iii) The
intensity of scattered light increases as decreases. Data are
presented which suggest that this increase is due to the formation of an
intermediate cubic phase, as predicted by recent theoretical suggestions of the
underlying universal phase sequence.Comment: 12 pages, typed using REVTEX 2.
Striped instability of a holographic Fermi-like liquid
We consider a holographic description of a system of strongly-coupled
fermions in 2+1 dimensions based on a D7-brane probe in the background of
D3-branes. The black hole embedding represents a Fermi-like liquid. We study
the excitations of the Fermi liquid system. Above a critical density which
depends on the temperature, the system becomes unstable towards an
inhomogeneous modulated phase which is similar to a charge density and spin
wave state. The essence of this instability can be effectively described by a
Maxwell-axion theory with a background electric field. We also consider the
fate of zero sound at non-zero temperature.Comment: 16 pages, 9 figures; v2: added discussion and one figure. Typos
correcte
Topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite coatings on carbon fibre-reinforced poly(etheretherketone)
In the present study, topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite (HA) coatings on carbon fibre-reinforced polyetheretherketone (CF/PEEK) was performed. VPS-Ti coatings with high roughness values (Ra=28.29±3.07 μm, Rz=145.35±9.88 μm) were obtained. On this titanium, intermediate layer HA coatings of various thicknesses were produced. With increasing coating thickness, roughness values of the HA coatings decreased. A high increase of profile length ratio, Lr, of the VPS-Ti coatings (Lr=1.45) compared to the grit-blasted CF/PEEK substrate (Lr=1.08) was observed. Increasing the HA coating thickness resulted in a reduction of the Lr values similar to the roughness values. Fractal analysis of the obtained roughness profiles revealed that the VPS-Ti coatings showed the highest fractal dimension of D=1.34±0.02. Fractal dimension dropped to a value of 1.23-1.25 for all HA coatings. No physical deterioration of the CF/PEEK substrate was observed, indicating that substrate drying and the used VPS process parameter led to the desired coatings on the composite material. Cross-section analysis revealed a good interlocking between the titanium intermediate layer and the PEEK substrate. It is therefore assumed that this interlocking results in suitable mechanical adhesive strength. From the results obtained in this study it is concluded that VPS is a suitable method for manufacturing HA coatings on carbon fibre-reinforced PEEK implant material
Field-induced metal-insulator transition and switching phenomenon in correlated insulators
We study the nonequilibrium switching phenomenon associated with the
metal-insulator transition under electric field E in correlated insulator by a
gauge-covariant Keldysh formalism. Due to the feedback effect of the resistive
current I, this occurs as a first-order transition with a hysteresis of I-V
characteristics having a lower threshold electric field (\sim 10^4 Vcm^{-1})
much weaker than that for the Zener breakdown. It is also found that the
localized mid-gap states introduced by impurities and defects act as hot spots
across which the resonant tunneling occurs selectively, which leads to the
conductive filamentary paths and reduces the energy cost of the switching
function.Comment: 5 pages, 3 figures. A study on the metal-insulator transition in
correlated insulators was adde
NaOH treatment of vacuum-plasma-sprayed titanium on carbon fibre-reinforced poly(etheretherketone)
Carbon fibre-reinforced polyetheretherketone (CF-PEEK) substrates were coated with titanium by vacuum-plasma-spraying and chemically treated in 10 M sodium hydroxide (NaOH) solution. After NaOH treatment, the specimens were immersed in simulated body fluid (SBF) containing ions in concentrations similar to those of human blood plasma. Scanning electron microscopy, energy-dispersive X-ray analysis and diffuse reflectance Fourier transformed-infrared spectroscopy were used to analyse the NaOH-treated VPS-Ti surface and the calcium phosphate layer formed during immersion in SBF. It was observed that a carbonate-containing calcium phosphate layer was formed on the NaOH-treated VPS-Ti surface during immersion in SBF, whereas no calcium phosphate precipitation occurred on the untreated surfaces. It is therefore concluded that vacuum-plasma-spraying with titanium and subsequent chemical modification in 10 M NaOH solution at 60°C for 2 h is a suitable method for the preparation of bioactive coatings for bone ongrowth on CF-PEE
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