Anomalous Hall effect

The dependence of the Hall resistivity (Formula presented) on the magnetic induction B was investigated on (Formula presented) single crystals and molecular-beam-epitaxy-grown layers. The strength of anomalous contributions to (Formula presented) found in most samples critically depends on the growth conditions. Measurements of the magnetization M were performed on single crystals. Measurements of (Formula presented) and (Formula presented) were performed on the same sample. It is shown that the anomalous contributions to (Formula presented) have a magnetic origin. The measurements of M and the results of neutron diffraction gave no indication of a magnetic phase transition of (Formula presented) It is suggested that the cause of the anomalous contributions to the Hall resistivity found in most samples investigated is of extrinsic nature. We propose that the effects arise from clusterlike regions which carry large magnetic moments and behave superparamagnetically.