Nature of the electromagnetic force between classical magnetic dipoles

The Lorentz force law of classical electrodynamics states that the force F exerted by the magnetic induction B on a particle of charge q moving with velocity V is given by F=qVxB. Since this force is orthogonal to the direction of motion, the magnetic field is said to be incapable of performing mechanical work. Yet there is no denying that a permanent magnet can readily perform mechanical work by pushing/pulling on another permanent magnet -- or by attracting pieces of magnetizable material such as scrap iron or iron filings. We explain this apparent contradiction by examining the magnetic Lorentz force acting on an Amperian current loop, which is the model for a magnetic dipole. We then extend the discussion by analyzing the Einstein-Laub model of magnetic dipoles in the presence of external magnetic fields.Comment: 6 pages, 2 figures, 20 equations, 6 reference

Magnetic field relaxation in ferromagnetic Ising systems

We analyze the thermal magnetization reversal processes in magnetic grains. Two experiments are carried out: swtiching time and switching field experiments. In both cases, we find that the simulated behavior is coherent with existing experimental data (the streched exponent of the switching time experiment increases with the temperature and is superior to unity; there exists a master curve for the switching field experiment). Moreover, we simulated magnetic grains in a region of parameters where no experimental data are available. We find that the relaxation time distribution $P(\ln{\tau})$ is gaussian, and we find the existence of a strong field regime.Comment: 9 pages, 7 figures, J.M.M.

Current-Induced Magnetization Switching in Permalloy-based Nanopillars with Cu, Ag, and Au

We compare magnetoresistances (MR) and switching currents (I_s) at room temperature (295K) and 4.2K for Permalloy/N/Permalloy nanopillars undergoing current-induced magnetization switching (CIMS), with non-magnetic metals N = Cu, Ag, and Au. The N-metal thickness is held fixed at 10 nm. Any systematic differences in MR and I_s for the different N-metals are modest, suggesting that Ag and Au represent potentially viable alternatives for CIMS studies and devices to the more widely used Cu.Comment: Submitted for Magnetism Conference, MMM-0

Injecting, Controlling, and Storing Magnetic Domain Walls in Ferromagnetic Nanowires

Domain walls in ferromagnetic nanowires are important for proposed devices in recording, logic, and sensing. The realization of such devices depends in part on the ability to quickly and accurately control the domain wall from creation until placement. Using micromagnetic computer simulation we demonstrate how a combination of externally applied magnetic fields is used to quickly inject, move, and accurately place multiple domain walls within a single wire for potential recording and logical operations. The use of a magnetic field component applied perpendicular to the principle domain wall driving field is found to be critical for increased speed and reliability. The effects of the transverse field on the injection and trapping of the domain wall will be shown to be of particular importance

Spin-orbit coupling in the hydrogen atom, the Thomas precession, and the exact solution of Dirac's equation

Bohr's model of the hydrogen atom can be extended to account for the observed spin-orbit interaction, either with the introduction of the Thomas precession,1 or with the stipulation that, during a spin-flip transition, the orbital radius remains intact.(2) In other words, if there is a desire to extend Bohr's model to accommodate the spin of the electron, then experimental observations mandate the existence of the Thomas precession, which is a questionable hypothesis,(2) or the existence of artificially robust orbits during spin-flip transitions. This is tantamount to admitting that Bohr's model, which is a poor man's way of understanding the hydrogen atom, is of limited value, and that one should really rely on Dirac's equation for the physical meaning of spin, for the mechanism that gives rise to the gyromagnetic coefficient g = 2, for Zeeman splitting, for relativistic corrections to Schrodinger's equation, for Darwin's term, and for the correct 1/2 factor in the spin-orbit coupling energy.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Local Anodizing of a Newly Prepared Aluminum Micrometric Disk

A search through the literature reveals that the vast majority of studies about aluminum anodizing were conducted at the macroscale (i.e., from cm2 up to m2), while those focused on local anodizing (i.e., on surfaces of less than 1 mm2) are rare. The last ones either used insulating masks or were conducted in an electrolyte droplet. The present study describes on the one hand a new way to prepare aluminum microelectrodes of conventional disk-shaped geometry, and on the other hand the local anodizing of their respective aluminum micrometric top-disks. The influence of the anodizing voltage on anodic film characteristics (i.e., thickness, growth rate and expansion factor) was studied during local anodizing. Compared with the values reported for macroscopic anodizing, the pore diameter appears to be significantly low and the film growth rate can reach atypically high values, both specificities probably resulting from a very limited increase in the temperature on the aluminum surface during anodizing