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Dynamic responses of magnetic hysteresis loops in a few monolayer (ML) thick Co/Cu(001) films were studied using surface magneto-optic Kerr effect (SMOKE). For a fixed external field strength H0, the hysteresis loop area increases as a function of frequency with a power law and reaches a maximum at a resonance frequency Ω0. This Ω0 depends on the external periodic field strength as well as the thickness and roughness of the films. The thickness and roughness parameters were measured quantitatively using high-resolution low-energy electron diffraction. For a fixed film thickness, the Ω0 in the low field region is highly dependent on H0, which is consistent with the prediction from the mean field model. For two Co films with an equivalent thickness but different degrees of film roughness, the resonance frequency Ω0 is lower for the rougher films in all the field strengths studied. For a fixed field strength, the value of Ω0 decreases as Co film roughness increases in a few ML regime. The roughness dependency in Ω0 indicates that the slowing down in the magnetization reversal process is due to the increased film roughness.

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Articles you may be interested inEffect of Al ion implantation on the adhesion of Al films to SiO2 substrates Ultrathin Co films were epitaxially grown on a Cu͑001͒ surface with different initial roughness created by Ar ion sputtering. The roughness of the Cu substrate and the Co film were characterized by high resolution low energy electron diffraction. The measured angular profiles were compared with a diffraction theory for rough surfaces and the roughness parameters were extracted quantitatively. Magnetic hysteresis loops of these characterized films were measured by surface magneto-optic Kerr effect. The hysteresis loop shape and loop area can be related to the nanoscale roughness in the Co films. For the roughest film with interface width Ϸ1.2t, where t is the single atomic step height, the magnetization is reduced several fold compared with that of smooth films with interface width Ϸ0.5t. Also, the coercivity in the roughest film is the highest and there exists a wide range of nucleation centers and coercive fields for magnetic domain reversals. These are related to the high step density in the rough substrate as the pinning centers. The hysteresis loop changes its shape and area under a sinusoidal external magnetic field as functions of frequency and field amplitude for all films. For the smooth films in the low frequency and low field regimes the loop area shows a 2 3 power law scaling behavior. The 2 3 value of scaling exponents are consistent with the prediction of a dynamic mean field theory with a double-well energy barrier. For a film with the same interface width but different step density and lateral correlation length the scaling exponents deviate from 2 3 value drastically.