MAGNETIC MICROSTRUCTURES FROM MAGNETIC FORCE MICROSCOPY AND MONTE-CARLO SIMULATION IN COFE-AG-CU GRANULAR FILMS

CoFe-Ag-Cu granular films, prepared by rf sputtering, displayed magnet ic domain microstructures for ferromagnetic concentrations above about 32% at. and below the percolation threshold. All samples have a fee s tructure with an [111] texture perpendicular to the film plane. Magnet ic force microscopy (MFM) showed a variety of magnetic domain microstr uctures, extremely sensitive to the magnetic history of the sample, wh ich arise from the balance of the ferromagnetic exchange, the dipolar interactions and perpendicular magnetocrystalline anisotropy, MFM imag es indicate that in virgin samples, magnetic bubble domains with an ou t-of-plane component of the magnetization are surrounded by a quasicon tinuous background of opposite magnetization domains. The application of a magnetic field in different geometries drastically modifies the m icrostructure of the system in the remanent state: i) for an in-plane field, the MFM images show that most of the magnetic moments are align ed along the film plane, ii) for an out-of-plane field, the MFM signal increases about one order of magnitude, and out-of-plane striped doma ins with alternating up and down magnetization are stabilized. Numeric al simulations show that a variety of metastable domain structures (si milar to those observed experimentally) can be reached, depending on m agnetic history, in systems with competing perpendicular anisotropy, e xchange and dipolar interactions.