Stochastic dynamic simulations of fast remagnetization processes: recent advances and applications

Numerical simulations of fast remagnetization processes using the stochastic dynamics are widely used to study various magnetic systems. In this paper we first address several crucial methodological problems of such simulations: (i) the influence of the finite-element discretization on the simulated dynamics, (ii) choice between Ito and Stratonovich stochastic calculi by the solution of micromagnetic stochastic equations of motion and (iii) non-trivial correlation properties of the random (thermal) field. Next we discuss several examples to demonstrate the great potential of the Langevin dynamics for studying fast remagnetization processes in technically relevant applications: we present numerical analysis of equilibrium magnon spectra in patterned structures, study thermal noise effects on the magnetization dynamics of nanoelements in pulsed fields and show some results for a remagnetization dynamics induced by a spin-polarized current.Comment: Invited paper submittedto JEMS'04 (Dresden, Germany

Shape-dependent exchange bias effect in magnetic nanoparticles with core-shell morphology

We study the low-temperature isothermal magnetic hysteresis of cubical and spherical nanoparticles with ferromagnetic-core/antiferromagnetic-shell morphology, in order to elucidate the sensitivity of the exchange bias effect to the shape of the particles and the structural imperfections at the core-shell interface. We model the magnetic structure using a classical Heisenberg Hamiltonian with uniaxial anisotropy and simulate the hysteresis loop using the metropolis Monte Carlo algorithm. For nanoparticles with geometrically sharp interfaces, we find that cubes exhibit a higher coercivity and lower exchange bias field than spheres of the same size. With increasing interface roughness, the shape dependence of the characteristic fields gradually decays, and eventually, the distinction between cubical and spherical particles is lost for moderately rough interfaces. The sensitivity of the exchange bias field to the microstructural details of the interface is quantified by a scaling factor (b) relating the bias field to the net moment of the antiferromagnetic shell (Heb=bMAF+Ho). Cubical particles exhibit a lower sensitivity to the dispersed values of the net interfacial moment.This research was cofinanced by the European Social Fund and Greek national funds through the Research Funding Program ARCHIMEDES-III (MIS 383576)

Factors Effecting Studies in the Department of Industrial Informatics of the Kavala Institute of Technology

Information regarding students’ and education institutes’ progress is a barometer for the overall prestige of the education system in Greece. Scientific community, the relative ministries and the society demand the evaluation of students and education institutes. Higher education studies are one of the most important level of education in Greece and compose important time in the lives of young scientists. A long deliberation took place during the last years regarding the time that is consuming for higher education and whether it should be unlimited or it should be limited to an upper limit. Recently, a rule of (2ν+1) for the upper limit of studies has been set by the Greek state. The pass-mark of 10 has been abolished and a deliberation for possible integration and abolishment of departments has started. In this paper, we study data regarding duration of studies in the department of Industrial Informatics of the Kavala Institute of Technology. The goal of this study is to extract important conclusions for the students’ progress and for their evaluation for the department. The final conclusions can become an important tool for the department, in order to make the necessary actions for its better function

PROOF COPY 550210MMM P R O O F C O P Y 5 5 0 2 1 0 M M M Domain wall motion in nanowires using moving grids "invited…

The magnetization reversal process of Co nanowires was investigated using a moving mesh technique. The nucleation and expansion of reversed domains is calculated by solving the Gilbert equation of motion for different damping constants. The adaptive finite element method reduces the total CPU time by more than a factor of 4 as compared to a uniform mesh. Two different domain wall types are observed. For a wire diameter of dϭ10 nm transverse walls occur and gyromagnetic pression limits the domain wall velocity. The domain wall velocity increases from 50 to 520 m/s as the Gilbert damping constant increases from ␣ϭ0.05 to ␣ϭ1 at an applied field of 500 kA/m. For a diameter greater than 20 nm vortex walls are formed. The vortex mobility increases with decreasing damping constant. Thus velocities up to 2000 m/s are reached for a wire diameter of 40 nm, ␣ϭ0.05, and an applied field of 250 kA/m

2002), Time resolved micromagnetics using a preconditioned time integration method

Abstract A detailed description for the solution of the Landau-Lifshitz-Gilbert equation with the finite element method is given. The use of implicit time integration schemes with proper preconditioning is reported. Simulations of a single-phase magnetic nanoelement without surface roughness and a magnetic nanoelement with a granular structure are performed to investigate the influence of the microstructure on the numerical behavior. Nanoelements with a granular structure cause an inhomogeneous computational grid. In granular systems preconditioning for time integration speeds up the simulations by three orders of magnitude as compared to conventional time integration schemes like the Adams method.