Caracterización de las propiedades magnéticas de películas delgadas de Fe1-xGax crecidas epitaxialmente sobre ZnSe/GaAs (001)

摘要

In this work, the correlation between magnetic anisotropies, Ga concentration and magnetic properties was investigated in Fe1xGax thin _lms, grown on a ZnSe/GaAs(001) substrate. The range of analyzed concentrations varies from x = 0 up to 0:29, and thicknesses go from 55nm to 72 nm. Besides, magnetic activation reversal volumes were calculated. Firstly, using a VSM magnetic properties, such as saturation magnetization (Msat), remanence magnetization (Mrem), coercive field (HC) and saturation field (Hsat), were measured in order to analyze the correlation between x and anisotropies. For x = 0:18 and x = 0:20, a region of linear dependence on the MH curves was observed, from remanence up to almost saturation, which is correlated with the maxima in HC and Hsat and the minimum in Mrem. This linear dependence appears as a result of an out of plane anisotropy (Kn), which has been already observed in thin films of other materials, and constitutes an indicator of a striped pattern magnetic domain formation. Afterwards, using a MFM, the magnetic domain structure was imaged in remanence (after saturating the sample) to investigate the correlation between this structure and the magnetic properties measured previously. It was found, indeed, that the same samples exhibiting the M vs H linear dependence have a striped magnetic domain structure; which is again consistent with Kn. The magnetization has both an in-plane component, that points in the direction of applied field, and an out-of-plane component (z axis), which points alternately in z and z. Moreover, when the field applied for saturating the sample is in the out of plane direction, a bubble pattern is observed for the same samples because, in this case there is no special direction in the plane of the sample. Then, using a protocol known as DCD (plot), the remanence magnetization (MDCD) after applying a magnetic field (HDCD) was obtained, in order to calculate the irreversible magnetic susceptibility (irr). irr is related to the changes in magnetization due to irreversible processes associated with the inversion of M, which process is strongly associated to magnetic anisotropies. In addition, magnetic relaxation was measured for each sample and thus, magnetic viscosity (S) was obtained. It was found that the maximum S appears near HC, which is expected as the most important changes in magnetization occur in the vicinity of HC. Finally, with all measured values, activation volumes were calculated; the order of magnitude obtained varies from _ 105 nm3 for pure Fe to 104 nm3 for x = 0:29, with the minimum at x = 0:18. Again, this is consistent with the presence Kn for the samples with x = 0:18 and 0:20, as anisotropy energy increases with volume, which energetically favors small activation volumes.