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In this paper we show that the widely accepted method of the determination of Curie temperature (T C ) in (Ga,Mn)As samples, based on the position of the peak in the temperature derivative of the resistivity, completely fails in the case of non-metallic and low-T C unannealed samples. In this case we propose an alternative method, also based on electric transport measurements, which exploits temperature dependence of the second derivative of the resistivity upon magnetic field.Throughout the last two decades of extensive research, (Ga,Mn)As dilute ferromagnetic semiconductor has become a reference model material in which ferromagnetism comes from the coupling between local magnetic moments and delocalised holes.

We tried to repeat the observation of the ferromagnetic response in proton and He-irradiated carbon made by the group of Esquinazi et al. We used He + and H + beams focused on graphite sample. The amount of charge deposited in the sample was comparable to the amount of charge used by Esquinazi. Magnetic measurements were performed in SQUID magnetometer. The magnetization of the samples before and after irradiation was compared. We did not observe any ferromagnetic enhancement of magnetization of our irradiated samples. Even if experiment was not the same as Esqinazi's one, we can exclude some of the mechanisms of ferromagnetism proposed by Esquinazi.

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Magneto-transport properties of a Ga0.93Mn0.07As ferromagnetic semiconductor film with strong epitaxial strain (Ga0.7In0.3As buffer) have been studied. The observed magnetoresistance showed peculiar peaks at the magnetic fields corresponding to magnetization switching probed by Hall voltage. Computer simulations showed that these anomalies could originate from the formation of complex, island-like magnetic domains, and their propagation in the sample.