Atomic level micromagnetic model of recording media switching at elevated temperatures

An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures non-uniform reversal modes. The results are compared with traditional methods which employ the Landau-Lifshitz-Gilbert equations based on uniformly magnetized grains with assigned intrinsic temperature profiles for $M(T)$ and $K(T)$. Using nominal parameters corresponding to high-anisotropy FePt-type media envisioned for Energy Assisted Magnetic Recording, our results demonstrate that atomic-level reversal slightly reduces the field required to switch grains at elevated temperatures, but results in larger fluctuations, when compared to a uniformly magnetized grain model.Comment: 4 pages, 5 figure

Measurement and analysis of lightning induced voltages in aircraft electrical systems

Lightning induced voltages in aircraft electrical circuit

Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular XY Antiferromagnet: A Finite-Size Scaling Study

Histogram Monte-Carlo simulation results are presented for the magnetic-field -- temperature phase diagram of the XY model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions. Finite-size scaling results at the various transition boundaries are consistent with expectations based on symmetry arguments. Although a molecular-field treatment of the Hamiltonian fails to reproduce the correct structure for the phase diagram, it is demonstrated that a phenomenological Landau-type free-energy model contains all the esstential features. These results serve to complement and extend our earlier work [Phys. Rev. B {\bf 48}, 3840 (1993)].Comment: 5 pages (RevTex 3.0), 6 figures available upon request, CRPS 93-

Micromagnetic simulations of interacting dipoles on a fcc lattice: Application to nanoparticle assemblies

Micromagnetic simulations are used to examine the effects of cubic and axial anisotropy, magnetostatic interactions and temperature on M-H loops for a collection of magnetic dipoles on fcc and sc lattices. We employ a simple model of interacting dipoles that represent single-domain particles in an attempt to explain recent experimental data on ordered arrays of magnetoferritin nanoparticles that demonstrate the crucial role of interactions between particles in a fcc lattice. Significant agreement between the simulation and experimental results is achieved, and the impact of intra-particle degrees of freedom and surface effects on thermal fluctuations are investigated.Comment: 10 pages, 9 figure

Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media

The results of micromagnetic simulations are presented which examine the impact of thermal fluctuations on sweep rate dependent coercivities of both single-layer and exchange-coupled-composite (ECC) perpendicular magnetic recording media. M-H loops are calculated at four temperatures and sweep rates spanning five decades with fields applied normal to the plane and at 45 degrees. The impact of interactions between grains is evaluated. The results indicate a significantly weaker sweep-rate dependence for ECC media suggesting more robustness to long-term thermal effects. Fitting the modeled results to Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043 (2004)] is successful only in the case of single-layer media with the field normal to the plane.Comment: 7 pages, 14 figure

Magnetic-Field Induced First-Order Transition in the Frustrated XY Model on a Stacked Triangular Lattice

The results of extensive Monte Carlo simulations of magnetic-field induced transitions in the xy model on a stacked triangular lattice with antiferromagnetic intraplane and ferromagnetic interplane interactions are discussed. A low-field transition from the paramagnetic to a 3-state (Potts) phase is found to be very weakly first order with behavior suggesting tricriticality at zero field. In addition to clarifying some long-standing ambiguity concerning the nature of this Potts-like transition, the present work also serves to further our understanding of the critical behavior at $T_N$, about which there has been much controversy.Comment: 10 pages (RevTex 3.0), 4 figures available upon request, CRPS-93-0

Tricritical behavior of the frustrated XY antiferromagnet

Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding their criticality.Comment: J1K 2R1 4 pages (RevTex 3.0), 4 figures available upon request, Report# CRPS-94-0