Magnetization reversal of thin ferromagnetic elements with surface anisotropy

The magnetization reversal process in thin-film ferromagnetic elements with surface anisotropy of various shapes and sizes is investigated by means of numerical simulation. The dependence of the perpendicular and in-plane hysteresis loops on the element thickness and the value of the surface anisotropy constant is obtained. For sufficiently large values of the surface anisotropy constant the magnetization reversal of thin-film elements is shown to occur due to the nucleation of the buckling mode. For an elongated rectangular element the nucleation field of the buckling mode is proportional to the absolute value of the surface anisotropy constant, and inversely proportional to the element thickness.Comment: 7 pages, 7 figure

Interaction effects in assembly of magnetic nanoparticles

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau- Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments, and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters the intensity of magneto- dipole interaction is determined mainly by the cluster packing density eta = Np*V/Vcl, where Np is the average number of the particles in the cluster, V is the nanoparticle volume, and Vcl is the cluster volume. The area of the low frequency hysteresis loop and the assembly specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 < eta < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with increase of eta, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with increase of the thickness of nonmagnetic shells at the nanoparticle surfaces.Comment: The paper is accepted for Nanoscale Res. Let

Map of metastable states for thin circular magnetic nano-cylinders

Nano-magnetic systems of artificially shaped ferromagnetic islands, recently became a popular subject due to their current and potential applications in spintronics, magneto-photonics and superconductivity. When the island size is close to the exchange length of magnetic material (around 15 nm), its magnetic structure becomes markedly different. It determines both static and dynamic magnetic properties of elements, but strongly depends on their shape and size. Here we map this dependence for circular cylindrical islands of a few exchange lengths in size. We outline the region of metastability of "C"-type magnetic states, proving that they are indeed genuine and not a result of pinning on particle imperfections. A way to create the smallest particles with guaranteed magnetic vortex state at zero field becomes evident. It is expected that the map will help focus the efforts in planning of experiments and devices.Comment: 3 pages, 1 figur