Magnetization switching in nanoscale ferromagnetic grains: simulations with heterogeneous nucleation

We present results obtained with various types of heterogeneous nucleation in a kinetic Ising model of magnetization switching in single-domain ferromagnetic nanoparticles. We investigate the effect of the presence of the system boundary and make comparison with simulations on periodic lattices. We also study systems with bulk disorder and compare how two different types of disorder influence the switching behavior.Comment: 3 pages, 4 Postscript figure

Neutron scattering and mu SR investigations of quasi-one-dimensional magnetism in the spin=3/2 compound Li(3)RuO(4)

The S = 3/2, quasi-one-dimensional (1D) zig-zag chain Heisenberg antiferromagnet Li3RuO4 has been investigated using heat capacity, inelastic neutron scattering, neutron diffraction, and μSR measurements on a powder sample. Our neutron diffraction and μSR studies confirm a long-range ordering of the magnetic moments on the Ru5+ cations below 40 K. The magnetic excitations were measured at various temperatures above and below the three-dimensional (3D) ordering temperature in order to understand the broad peak observed in the temperature dependence of the magnetic susceptibility. At 5 K we have observed two well-defined magnetic excitations at 5.5 meV and 8.5 meV and a weak low-energy peak near ∼2 meV. We interpret the 5.5 meV energy peak as a 1D zone-boundary mode and that at 8.5 meV as arising from a maximum away from the zone boundary in the dispersion curve for spin-wave modes along the chain of Ru5+ ions. The weaker peak near 2 meV is thought to arise from a weak interchain coupling. Our data are best reproduced using a model with three intrachain interactions and one weak interchain interaction. The experimental spin-exchange interactions are in good agreement with those calculated for a 1D model by density functional theory (DFT) methods. Furthermore, above TN we observe strong diffuse scattering at the same Q-position as the 5.5 meV mode, which suggests the presence of short-range magnetic correlations above TN. We have estimated the correlation length ξ ∼ 2.9 at 50 K, which is close to 2.99, the shortest distance between the Ru5+ cations along the zig-zag chain. © 2011 American Physical Society