190 research outputs found
Systematic model behavior of adsorption on flat surfaces
A low density film on a flat surface is described by an expansion involving
the first four virial coefficients. The first coefficient (alone) yields the
Henry's law regime, while the next three correct for the effects of
interactions. The results permit exploration of the idea of universal
adsorption behavior, which is compared with experimental data for a number of
systems
Ratchet propagation of a magnetic domain wall in a single magnetic wire with quantum interference
Quantum interference incorporating spatially asymmetric potential profiles is
realized experimentally to manipulate a magnetic domain wall (DW) into a single
multilayered wire whose spacer has a thickness gradient for generating
asymmetrical interlayer exchange coupling from side to side. We demonstrate
experimentally how to guide a DW in a micron-scale ferromagnetic wire without
reflection symmetry of the interlayer exchange coupling. This is the ratcheting
of a DW in a form of ratchet potential using quantum interference. The
experimental results can be described well by numerical simulations considering
spatially asymmetric potential profiles due to quantum interference
Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?
We have observed a superparamagnetic to ferromagnetic transition in films of
isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance
(MR) of the films was measured as a function of the overlayer thickness.
Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As
different materials were deposited onto the grains hysteresis developed in the
MR. This behavior is ascribed to an increase of the typical domain size due to
magnetic coupling between grains. The strength of the inter-grain coupling is
found to correlate with the magnetic susceptibility of the overlayer material.
We discuss possible mechanisms for this coupling and suggest that the data may
reflect the existence of a magnetic proximity effect (analogous to the
well-known effect in superconductivity) in which a ferromagnetic moment is
induced in the metallic non-magnetic medium.Comment: 4 pages, 5 figure
Magnetic tunnel junction magnetic field sensor design tool
A spreadsheet-based magnetic tunnel junction (MTJ) sensor design tool is presented in this paper. The system is developed using Excel and Visual Basic Application. It allows users to optimize the various parameters of the sensor design with the goal of SQUID-like sensitivity. Users can input parameters of the design including magnetic properties, junction areas, and free layers thicknesses. The design tool will then calculate and display automatically various noise sources including Johnson noise, shot noise, 1/f noise, and thermal magnetic noise that must be considered when building MTJ magnetic field sensors. Graphs predicting the sensitivities, operating current and power of the finished sensors are shown and fine tuning of each design parameter is allowed using the scrollbars provided. Using this design tool, effects of changes made to any design parameter can be clearly observed and detailed noise analysis can be studied without manually repeating complex calculations. ©2010 IEEE.published_or_final_versionThe 3rd International Nanoelectronics Conference (INEC 2010), Hong Kong, China, 3-8 January 2010. In Proceedings of the 3rd INEC, 2010, p. 1149-115
Direct Imaging of Coexisting Ordered and Frustrated Sublattices in Artificial Ferromagnetic Quasicrystals
We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins
Spin waves in ultrathin ferromagnetic overlayers
The influence of a non-magnetic metallic substrate on the spin wave
excitations in ultrathin ferromagnetic overlayers is investigated for different
crystalline orientations. We show that spin wave dumping in these systems occur
due to the tunneling of holes from the substrate into the overlayer, and that
the spin wave energies may be considerably affected by the exchange coupling
mediated by the substrate.Comment: RevTeX 4, 7 pages, 5 figures; submitted to Phys. Rev.
Electronic Theory for the Nonlinear Magneto-Optical Response of Transition-Metals at Surfaces and Interfaces: Dependence of the Kerr-Rotation on Polarization and on the Magnetic Easy Axis
We extend our previous study of the polarization dependence of the nonlinear
optical response to the case of magnetic surfaces and buried magnetic
interfaces. We calculate for the longitudinal and polar configuration the
nonlinear magneto-optical Kerr rotation angle. In particular, we show which
tensor elements of the susceptibilities are involved in the enhancement of the
Kerr rotation in nonlinear optics for different configurations and we
demonstrate by a detailed analysis how the direction of the magnetization and
thus the easy axis at surfaces and buried interfaces can be determined from the
polarization dependence of the nonlinear magneto-optical response, since the
nonlinear Kerr rotation is sensitive to the electromagnetic field components
instead of merely the intensities. We also prove from the microscopic treatment
of spin-orbit coupling that there is an intrinsic phase difference of
90 between tensor elements which are even or odd under magnetization
reversal in contrast to linear magneto-optics. Finally, we compare our results
with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We
conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the
magnetic structure and in particular the magnetic easy axis in films and at
multilayer interfaces.Comment: 23 pages Revtex, preprintstyle, 2 uuencoded figure
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