ac susceptibility of a ferromagnetic semiconductor (Ga,Mn)As was measured using microscaled Hall bar through the anomalous Hall effect. The synchronous component of the Hall resistance with applied ac magnetic field (∼1 mT) was detected using a lock-in technique. The temperature dependence of the ac Hall resistance shows a clear peak in the vicinity of the Curie temperature TC, when an offset dc field, whose magnitude is comparable to that of the ac field, is superimposed. We applied this method to detect the change of TC as a function of hole concentration by applying electric fields.
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