We used polarized neutron reflectometry to determine the temperature dependence of the magnetization of thin AuFe films with 3% Fe concentration. We performed the measurements in a large magnetic field of 6 T in a temperature range from 295 to 2 K. For the films in the thickness range from 500 to 20 nm we observed a Brillouin-type behavior from 295 K down to 50 K and a constant magnetization of about 0.9 micro(B) per Fe atom below 30 K. However, for the 10 nm thick film we observed a Brillouin-type behavior down to 20 K and a constant magnetization of about 1.3 micro(B) per Fe atom below 20 K. These experiments are the first to show a finite-size effect in the magnetization of single spin-glass films in large magnetic fields. Furthermore, the ability to measure the deviation from the paramagnetic behavior enables us to prove the existence of the spin-glass state where other methods relying on a cusp-type behavior fail. 相似文献
A method is proposed for overcoming the famous ‘phase problem’ in neutron specular reflectometry. It is shown that the complex reflection coefficient of any unknown non magnetic layer, with real scattering length density, can be determined by using a magnetic transmitted media and by measuring the polarization of the reflected beam relative to the incident beam. The method follows directly from a recent one which is limited to a one-dimensional neutron polarization. Here, the theory is generalized for a neutron polarization of arbitrary direction. We show that some combinations between the polarization of the incident and reflected beam must be used to determine the reflection coefficient. Also, it is shown that instead of full polarization or reflectivity analysis, some combinations between polarization and reflectivity can be used in the analysis process. The method is supplemented with a schematic example to test the method and its stability in the presence of experimental uncertainties and roughness of the interfaces. PACS 61.12.Ha; 28.20.-v 相似文献
We study theoretically the behavior of nanoscopic liquid films L (thickness e) intercalated between a solid S and a rubber R (elastic modulus μ). Thickness modulations involve a healing length , which results from a competition between elastic and disjoining pressure. With van der Waals interactions, , where a is a molecular size and h0 the rubber capillary length ( , interfacial tension). If the Hamaker constant of the intercalated liquid is negative, the film dewets by amplification of
peristaltic fluctuations (“spinodal dewetting”). The typical size of the contacts is predicted to scale like for films of thicknesses . The rise time of the fastest mode, predicted to scale like , should be very sensitive to the film thickness.
Received 11 February 2000 and Received in final form 22 May 2000 相似文献
Recently it has been shown that the modulus and phase of complex reflection coefficient can be determined using a magnetic substrate and polarized neutrons. Several other methods have also been worked out based on the measurement of polarizations of reflected neutrons from magnetic reference layers and magnetic substrate. However, due to the fact that available reflectometers are limited in the choice of polarization of reflected beam in the same direction as the polarization of the incident beam, neither of the methods, which are based on polarization analysis, have been proven to be experimentally practical. In this paper, we have proposed a new method for determining the phase of reflection coefficient that is based on two measurements of polarization, which correspond to two magnetic fields with the same magnitude and different orientations. The polarization analysis is performed in the same direction as the polarization of the incident beam and is well suited for available reflectometers.The problems envisaged in implementation of the method are also discussed. 相似文献
The evolution of the magnetic structure of multilayer [Fe (35 Å)/Gd (50 Å)5] with variation in temperature and an applied magnetic field was determined using a complementary approach combining polarized neutron and X-ray resonant magnetic reflectometry. Self-consistent simultaneous analysis of X-ray and neutron spectra allowed us to determine the elemental and depth profiles in the multilayer structure with unprecedented accuracy, including the identification of an inhomogeneous intralayer magnetic structure with near-atomic resolution. 相似文献
Using the polarized neutron reflectometry method, we studied Au/SiO2 + Co(60 at %)/GaAs granular films, which display a giant injection magnetoresistance effect in a narrow temperature range
close to T = 300 K. We revealed the existence of a layer having particular magnetic properties at the boundary of a film with a semiconductor
GaAs substrate. Experiments carried out at temperatures T = 300 K and T = 100 K showed an insignificant difference in the magnetic profile of the heterostructure. 相似文献
Measurements of the reflection of thin silver films are reported which have been performed with the ATR method at constant wavelength λ as well as at constant angle of incidence θ. The backbending of the reflection minimum as a function of θ at constant λ is discussed. The influence of the interband absorption determines the R(θ,λ) dependence. Surface roughness displaces the turning point in the backbending curve. 相似文献
Attenuated total reflection and photoacoustic measurements have been employed to study the decay channels of plasmon surface polaritons optically excited at the Ag-air interface. We show that it is possible to analyse the radiative and non-radiative decay quantitatively by comparing measurements taken with transparent and blackened cavities, respectively. In the first case only light that is thermalized by radiationless processes in the Ag film produces a photoacoustic signal. In the blackened cell, however, light that is either transmitted through the Ag film or reemitted by the radiative decay of excited polaritons also contributes to the photoacoustic intensity. 相似文献
Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic “shaking” of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which “liquefies” upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions. 相似文献
X-ray and neutron reflectivity measurements provide a wealth of information on thickness and interfacial properties on the nanometer scale. This method is therefore well suited for the study of nano-structured thin films and superlattices. Neutrons provide a different contrast between the elements than X-rays and, in addition, are sensitive to the magnetization in the sample. Using polarized neutrons, magnetic as well as chemical profiles can be probed. In this review a basic introduction into the theory of X-ray and neutron reflectivity is provided along with some recent examples including the oxidation of Fe films and the structural and magnetic properties of Co/Cu superlattices. 相似文献
Nano and microcrystalline ZnO thin films were prepared on glass substrates using pulsed laser deposition technique under a vacuum of 3 × 10−7 Torr at different laser power density. Composition analyses show that the films deposited at low laser power density have more structural defects than the film deposited at high laser power density. It confirms that the content of Zn in free-state decreased greatly at high laser power density. Atomic force microscopy analysis shows that the surface roughness of the deposited films increases with an increase in laser power density. X-ray diffraction analyses show that all the films are oriented along (0 0 2) direction independently on the laser power density applied. The structural quality increases with an increase in laser power density. It is due to the fact that the increase of laser power density leads to the enhancement of peak intensity. The increase of laser power density reduces the film transmission in the visible range of the spectra. The optical band gap value is found to be in the range from 3.42 to 3.39 eV. It shows that the optical band gap value decreases with an increase in laser power density. FTIR analysis shows that the hydrated oxide content in the deposited films decreases with an increase in laser power density. 相似文献
The magnetic and structural properties of epitaxial Fe films grown on Si(1 1 1) are investigated by polarized neutron reflectometry (PNR) at room temperature. The influence of different types of interfaces, Fe/Si, Fe/FeSi2 and Au/Fe on the magnetic properties of Fe films deposited by molecular beam epitaxy onto Si(1 1 1) are characterized. We observe a drastic reduction of the magnetic moment in the entire Fe film deposited directly on the silicon substrate essentially due to strong Si interdiffusion throughout the whole Fe layer thickness. The use of a silicide FeSi2 template layer stops the interdiffusion and the value of the magnetic moment of the deposited Fe layer is close to its bulk value. We also evidence the asymmetric nature of the interfaces, Si/Fe and Fe/Si interfaces are magnetically very different. Finally, we show that the use of Au leads to an enhancement of the magnetization at the interface. 相似文献
We have utilized the polarized neutron scattering technique for the determination of the nuclear temperature in copper from 20 mK down to 100 K. Using a cooling facility where two adiabatic demagnetization stages work in series we have calibrated the flipping ratio of neutrons scattered from the (200) Bragg-peak against the nuclear polarization over the whole polarization range. The observed calibration curve deviates considerably from the curve expected for an extinction-free sample. The polarized neutron thermometer is discussed and applied in measurements of the spin-lattice relaxation in copper. 相似文献
We study the surface dynamics of silica films grown by low pressure chemical vapor deposition. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state compatible with the Kardar-Parisi-Zhang (KPZ) equation in three dimensions. At intermediate times the surface undergoes an unstable transient due to shadowing effects. By varying growth conditions and using spectroscopic techniques, we determine the physical origin of KPZ scaling to be a low value of the surface sticking probability, related to the surface concentration of reactive groups. We propose a stochastic equation that describes the qualitative behavior of our experimental system. 相似文献