SURVEY OF THE DEPENDENCE ON TEMPERATURE OF THE COERCIVITY OF GARNET-FILMS

The temperature dependence of the domain-wall coercive field of epitaxial magnetic garnets films has been investigated in the entire temperature range of the ferrimagnetic phase, and has been found to be described by a set of parametric exponents. In subsequent temperature regions different slopes were observed, with breaking points whose position was found to be sample dependent. A survey ba.ed on literature Data as well as on a large number of our own samples shows the general existence of this piecewise exponential dependence and the presence of the breaking points. This type of domain-wall coercive field temperature dependence was found in all samples in the large family of the epitaxial garnets (about 30 specimens of more than ten chemical compositionsj and also in another strongly anisotropic material (TbFeCo)

Three-Dimensional Micromagnetic Simulation of Spatial Distribution of Magnetization in Thick Cobalt Layers

Spatial magnetization distribution of cobalt layer is studied by means of three-dimensional micromagnetic simulations in the range of cobalt thickness d from 21 to 249 nm. In this range, a spin-reorientation phase transition occurs, while the cobalt thickness increases, from a state with in-plane magnetization, to a state with out-of-plane components of magnetization. An infinite cobalt layer is modelled by the 750 nm × 750 nm × d structure consisting of cubic cells of size of 3 nm and the periodic boundary conditions. For larger thicknesses, a labyrinth, partially closed, stripe structure has been found

Phase diagram of vortex lattice on a square pinning array in superconducting films

We have analyzed the phase transitions in a square lattice of vortices using the thermodynamic approach. For a square array of the artificially created pin centers in \chem{Nb} superconducting film we have calculated the phase diagram, which reveals the re-entrant melting features. We explain this effect by the nonmonotonic temperature dependence of the vortex-vortex interaction potential

Drastic changes of the domain size in an ultrathin magnetic film

A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is predicted. The domain size has been experimentally studied in a 1 nm Co film characterized by a square hysteresis loop. The investigations have been performed by polar Kerr based microscopy and magnetic force microscopy. The domain structure of two remnant states generated by applying an in-plane and a perpendicular magnetic field has been compared. Drastically, the smallest domain size has been observed for the former.The authors are grateful to Professor J. Miltat for fruitful discussions concerning MFM imaging and Dr. M. Tekielak for magneto-optical imaging. J. M. Garcia wishes to thank the European Community for his Marie Curie Fellowship. This work was supported by the Polish State Committee for Scientific Research (Grant No. 4 T08A 025 23), ESF NANOMAG project and European Commission program ICA1-CT-2000-70018 (Center of Excellence CELDIS).Peer reviewe