Results of magnetization, magnetotransport and Mössbauer spectroscopy measurements of sequentially evaporated Fe-Ag granular composites are presented. The strong magnetic scattering of the conduction electrons is reflected in the sublinear temperature dependence of the resistance and in the large negative magnetoresistance. The simultaneous analysis of the magnetic properties and the transport behavior suggests a bimodal grain size distribution. A detailed quantitative description of the unusual features observed in the transport properties is given.
Adsorption of N2 was studied on zeolite H-Y, ultrastabilized H-Y (H-USY), H-mordenite, H-ZSM-5, H-beta, and on sulfated zirconia-titania (SZT) mixed oxide by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at 298 K and at N2 pressures up to 9 bar. The adsorption-induced DeltanuOH red-shift of the nuOH bands was used as a measure of the intrinsic acid strength of the Brnønsted acid sites. The intrinsic acid strength of the solids follows the order of H-ZSM-5 approximately H-mordenite approximately H-beta > H-USY > SZT approximately H-Y. The solids were characterized by their hexane conversion activities at 553 K and 6.1 kPa hexane partial pressure. The reaction was shown to proceed predominantly by a bimolecular mechanism, while the reaction was first order in hexane and zero order in alkenes. The site-specific apparent rate constant of the bimolecular hexane conversion was shown to parallel the intrinsic acid strength of the samples, suggesting that the ratio of the apparent and the intrinsic activity, that is, the KA' equilibrium constant of alkane adsorption on the hydrocarbon-covered sorption sites, is hardly dependent on the catalyst structure.
The formation mechanism of 360° domain walls (360DW) created in an exchange-biased bilayer of Co65.5Fe14.5B20/Ir22Mn78 is described. The structural and magnetic properties are experimentally characterized and incorporated into a micromagnetic model of exchange-bias for granular anti-ferromagnetic films. This model is used to study and explain the formation mechanism of 360DWs in the ferromagnetic layer, which occur due to interface coupling to the antiferromagnetic layer. The validity of the resulting calculated magnetization maps are examined by comparing simulated and experimental Fresnel-contrast images of the bilayer. Energy barrier simulations are used to explain the dependence of the areal size and spatial frequency of the 360DW on the anisotropy energy of the anti-ferromagnetic layer. These calculations also show how such structures can form at room temperature at relatively low applied magnetic fields. Calculations based on this model are in agreement with imaging using Lorentz transmission electron microscopy and the measured macro-magnetic properties.
In this article we describe the thermal relaxation in anti-ferromagnetic/ferromagnetic bilayers using a hybrid method that combines a kinetic Monte Carlo technique with magnetization dynamics following the Landau Lifshitz Gilbert equation. A granular anti-ferromagnetic layer is exchange coupled to an amorphous ferromagnetic layer and discretized using a finite element method. Calculations are made to help clarify how the underlying magnetic structure is related to the measured exchange bias fields as a function of temperature for the case of amorphous Co65.5Fe14.5B20/granular Ir22Mn78 bilayers. Our calculations are in excellent agreement with experimentally measured macro-magnetic properties of these bilayers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.