Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars

Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model incorporating thermal fluctuations and dipole-dipole interactions (calculated by the Fast Multipole Method) are presented for systems composed of nanoscale iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated under sinusoidally varying fields are obtained, while the coercive field is estimated to be 1979 $\pm$ 14 Oe using linear field sweeps at T=0 K. Thermal effects are essential to the relaxation of magnetization trapped in a metastable orientation, such as happens after a rapid reversal of an external magnetic field less than the coercive value. The distribution of switching times is compared to a simple analytic theory that describes reversal with nucleation at the ends of the nanomagnets. Results are also presented for arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a separation of 300 nm, where the field from neighboring pillars is only $\sim$ 1 Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of numerical technique

Corners and nucleation in Micromagnetics

The divergence of the stray field in corners and its consequence for micromagnetic calculations was studied numerically in two dimensions for high-anisotropy materials. The results show that no atomistic theory has to be invoked because the singularity is smoothed out already within micromagnetics. The magnetic configurations and its deduced critical quantity, the coercivity, are determined correctly if the configurations are well approximated on the exchange length SQRT(A/Kd). The singularity in the stray field remains only visible in the torque balance where it is compensated by an exchange torque

Switching behavior of small soft magnetic elements

Hysteretic properties of submicron-sized soft magnetic elements as they might be used in integrated field sensors are computed. A new 3D micromagnetic simulation program was used which requires only workstation computing power. Results are scrutinized using previously established techniques. The influence of object shape and size is investigated and related to experimental findings reported in the literature

Micromagnetic simulations of the domain structure and the magnetization reversal of Co50Ni50/Pt multilayer dots

The domain structure and the switching field of Co50 Ni50 /Pt multilayer dots,prepared by laser interference lithography,were micromagnetically simulated.The simulations were carried out with a three-dimensional simulation package,optimized for large-scale problems. The single-domain state is the lowest energy state for dots with a diameter below 75 nm.The switching field was computed by using suitable minimization techniques,and was used to analyze the effect of size,dot shape and edge defects

A read and write element for magnetic probe recording

We present our results on the development of magnetic sensors for application in magnetic probe recording. Successful writing experiments on a magnetic medium with perpendicular anisotropy show that magnetic domains of 130 nm can be reversed in a heat-assisted process. For reading purposes we propose a magnetoresistive sensor. The optimization of the shape of the sensor was performed using micromagnetic simulations with the requirement that the sensor has to be capable of both read and write operations. At this stage, the experimental realization of the sensor was carried out at a wafer-base level. The fabrication technique consists of a combination of optical lithography and focused ion beam etching