  In this work we report results of ferromagnetic resonance studies of a 6% 15
nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were
performed with in-plane oriented magnetic field, in the temperature range
between 5K and 120K. We observe a temperature induced reorientation of the
effective in-plane easy axis from [-110] to [110] direction close to the Curie
temperature. The behavior of magnetization is described by anisotropy fields,
H_{eff} (= 4\piM -H_{2\perp}), H_{2\parallel}, and H_{4\parallel}. In order to
precisely investigate this reorientation, numerical values of anisotropy fields
have been determined using powerful - but still largely unknown - interval
calculations. In simulation mode this approach makes possible to find all the
resonance fields for arbitrarily oriented sample, which is generally
intractable analytically. In 'fitting' mode we effectively utilize full
experimental information, not only those measurements performed in special,
distinguished directions, to reliably estimate the values of important physical
parameters as well as their uncertainties and correlations.
