Intrinsic
Anomalous Hall and Anomalous Nernst Effects in Ga1-xMnxAs Ferromagnetic
Semiconductors
Jing Shi, Department of Physics and Astronomy,
University of California, Riverside, USA
The physical origin of the anomalous Hall effect (AHE) in ferromagnets
has been a topic of long-standing theoretical and experimental debate. The Hall
current may or may not depend on scattering, which is called extrinsic or
intrinsic, respectively, and it has not been settled completely. To help
resolve this issue, we carried out a systematic study of both electrical and
thermoelectric transport properties in Mn-doped GaMn ferromagnetic semiconductors. We observed a very large
anomalous Nernst effect (ANE) - thermoelectric counterpart of AHE, which is
directly related to the magnetization instead of the applied magnetic field.
Unlike AHE that remains positive below the Curie temperature, ANE can switch
its sign at low temperatures. We show that the sign change in ANE is the first
indication that the Hall and Nernst currents are not extrinsic. We
further analyzed the temperature dependence of ANE using all measured transport
coefficients and obtained excellent agreement which quantitatively yields the
exponent of the power-law between Rxx and Rxy. Out results show the intrinsic nature of the
Hall and Nernst currents in GaMnAs. Meanwhile,
we experimentally established the Mott relation for the first time for the
intrinsic anomalous transport coefficients recently shown by theorists.