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(Color online) (a) Hysteresis loops of for different thicknesses of ferromagnetic GaMnAs layers. (b) Dependence of coercivity and exchange bias fields on . The solid lines are curves fitted to experimental data to allow comparison of our results with the widely reported dependence of and in metallic AFM/FM systems. The fitted exponents equal for (thick line) and for (thin line).
(Color online) FMR spectra for the sample with a thick GaMnAs layer, obtained in (a) ZFC and (b) FC experiments, for two opposite orientations of magnetic field. (c) Dependence of unidirectional anisotropy field on . The solid line was fitted from the same equation as that used in Fig. 1(b), with giving the best fit. (d) Anisotropy exchange energies and obtained from the hysteresis loop and the FMR data, respectively.
(Color online) (a) Temperature dependence of FMR positions for two opposite directions of magnetic field, obtained after initial FC (black) and after subsequent ZFC to (red). The lines joining the points are guides for the eyes. Both sets of data were interpolated numerically for the same values of in order to allow for possible temperature drift. (b) Unidirectional anisotropy field , calculated from data. Note that after first temperature scan up to the sample was again zero field cooled, and the experiment repeated, showing a very similar behavior (marked “second heating”).
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