Magnetic field computation in a non-oriented sheet cross-section considering the hysteresis phenomenon

The aim of the present work is the numerical computation of the average magnetic induction in the cross-section of a non-oriented 3% Si-Fe sheet by solving the magnetic diffusion equation. Jiles’ dynamic model is used to describe the magnetization law. The obtained results are compared with those of the measurements carried out for frequencies of 0.5, 50, 200 and 500 Hz. A satisfactory agreement is obtained between both types of results.     

Many-body theory of magnetization of Bloch electrons in the presence of spin-orbit interactions

We derive a theory of magnetization of an interacting electron system in the presence of a periodic potential, spin-orbit interaction and an applied magnetic field in the paramagnetic limits. Starting from a thermodynamic potential, which includes both the quasi-particle and correlation contributions, we show that modifications brought about by the electron-electron interactions for the magnetization in the quasi-particle approximation is precisely cancelled by the contributions due to electron correlations.This is in contrast to the explicit many-body effects seen in case of the magnetic susceptibility and the Knight-shift. The magnetization is expressed as a product of the spin-density and the effective g-factor, mainly due to the spin-orbit interaction. We show the importance of self-energy corrections on the single-particle energy spectrum by considering a variant of the Hubbard Hamiltonian in momentum space.     

Magnetoresistance measurement of permalloy thin film rings with triangular fins

Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.     

Homogeneous-inhomogeneous transitions in a Landau level with spin splitting

The homogeneous-inhomogeneous transitions of a two-dimensional electron gas in a strong perpendicular magnetic field are studied in the particular case when half of the states in a spin splitted Landau level are occupied. To this end the dielectric susceptibility in the homogeneous states as well as the free energy in the modulated states are calculated. Unless theg factor dos not exceed a certain value the charge-density waves are stable in an interval of finite temperatures.     

Ab initio molecular dynamics simulations of the Li4F4 cluster

Molecular dynamics simulations have been performed directly on the ab initio potential energy surface of Li₄F₄, which was generated within the Hartree-Fock approximation using a Gaussian basis set (split valence contraction). Trajectories at different temperatures yield the temperature dependence of the infrared spectra and the photoelectron spectra. For the infrared spectra comparison is made with MD results using a shell model ion pair potential function.     

Experimental analysis of the fast magnetization dynamics in high perpendicular anisotropy Co/Pt nanostructures

We present preliminary results for magnetization dynamics in high perpendicular anisotropy Co/Pt cross-shaped nanostructures submitted to a single/train out-of-plane field pulses. For this, a fabrication process has been developed to obtain high-quality microwave test structures. Using extraordinary Hall effect, we measure quasistatic hysteresis loops while applying either a single or a train of field pulses of given amplitude (32 mT at maximum), variable duration (0.2–10 ns) and repetition frequency (1–100 kHz). We get that field pulses affect only one side of the hysteresis loops without any clear change in the squareness of the loop. Such behavior can be most probably attributed to pulse-induced nucleation of reverse domains in the cross area. The measured shift in coercive field decreases linearly with the logarithm of the pulse duration and two switching regimes that get connected for pulse duration around 1 ns have been observed. Switching probability with single pulse showed that field pulse of 10 ns and 32 mT of magnitude has the same effect of 2 mT static fields.     

Twin-microstructure enhanced magnetoresistance in La0.67Ba0.33MnO3 oxides

The grain growth dependence of microstructure and its effects on magnetic and transport properties are studied in the polycrystalline La_0.67Ba_0.33MnO₃ oxides. It is found that a lateral growth manner along a certain direction and a concentric terrace pattern along three orthogonal axes occur in the samples sintered at 1573 and 1673 K, respectively. Lamella-like twin microstructure forms in the concentric terrace growth pattern and the magnetoresistance properties can be enhanced by the twin microstructure. It suggests that the twin-boundaries in twin-grains may possibly induce spin-dependent scattering of electrons that is field reduced, or spin-polarized tunneling of electrons that is field enhanced, thus strengthening the effect of grain boundaries.     

A tight-binding study of surface magnetic anisotropy of the Co (0001) and its perturbation by Cu and CO

Recent experiments show that on rather thick Co films deposition of Cu or adsorption of CO or C can switch the magnetization direction along the surface normal. We present semi-empirical self-consistent tight-binding calculations for a semi-infinite hcp Co(0001) crystal. It appears that the contribution of the magnetic anisotropy-energy from the surface layer favors the in-plane alignment of magnetic moments. Various surface perturbations (Cu deposition or CO adsorption, artificial suppression of surface magnetization), however, reduce this contribution considerably or even change the sign of the electronic part of the magnetic anisotropy energy, thus making conditions for perpendicular magnetization more favourable.