Magnetotransport measurement

The solid line in fig. 9 shows M determined by the transport measurements, where the Hall resistance is almost proportional to the perpendicular component of M, as described in the next section. The good agreement between M determined by SQUID and transport measurements indicates that one can correctly determine M of (Ga,Mn)As by magnetotransport measurements. 

Using a scanning Hall microscope, a stripe-shaped domain structure has been observed in a (Ga.Mn)As sample with tensile strain and perpendicular easy axis (Shono et al. 2000 Fukumura et al. 2001). The Baukhausen noise due to the scattering from the domain wall movement has also been observed in magnetotransport measurements (Hayashi et al. 2000). 

Due to the presence of the anomalous Hall effect (known also as the extraordinary or spin Hall effect), magnetotransport measurements provide valuable information on the magnetism of thin films. The Hall resistance / Haii is empirically known to be a sum of ordinary and anomalous Hall terms,... 

Magnetotransport measurements on n-type samples show no evidence for carrier-Mn spin interactions (Ohno et al. 1991). In particular, no magnetization-dependent anomalous Hall effect is observed within the experimental error. 

Fig. 21. Faraday rotation for a 2- m thick film of Ga Mn.rAs with x = 0.043 measured as a function of the photon energy in a magnetic field of 6 T at 10 and 300 K (a) and as a function of the magnetic field at 10 K, 1.55 eV and at 300 K, 1.49 eV (b). Solid lines show the magnetization determined from magnetotransport measurements at the given temperatures (scaled to match the open symbols) (Kuroiwa et al. 1998).

A portion of the film on SrTi03 shown in fig. 13(b) was patterned into a 16 urn wide line by reactive ion etdiing to measure the critical current density and for other magnetotransport measurements. Figure 14 shows the temperature dependence of the critical current density, J. It can been seen that at 77 K and in zero field, a current density of 0.69 x 10 A/cm is measured. The film critical current density is greater than 4 x 10 A/cstr at 50 K and in a field of 14 Tesla. More detailed magnetotransport results will be mentioned later. 

The magnetotransport measurements have been made on films with dimensions comparable to those formed on state-of-the-art supercOTducting devices. The number for the critical current density as well as the critical field are quite impressive for films processed at these low temperatures. 

With the possibihties d = x,y,z due to the AF orthorhombic symmetry. These gap functions have all an equatorial node line at = 0. Confirmation of the node structure has to await the results of angle resolved magnetotransport or specific heat measurements in the vortex phase and for a confirmation of the spin state the Knight shift measurements on high quality single... 

A discrete model for magnetotransport in percolating systems has been proposed 1220,221]. This model, which assumes that the conducting component has a closed Fermi surface and that the MR saturates at high fields, predicts a large MR in the vicinity of the percolation threshold. This is contrary to the predictions of effective medium theory in which there is no MR near the percolation threshold [235,236]. For insulating PANI-CSA (100%), the MR tends to saturate at 8 T, but it is not known whether the Fermi surface of PANI-CSA is open or closed. In order to address this question, we have carried out MR measurements in many PANI-CSA/ PMMA samples (0.4-1.5 vol %) near the percolation threshold in which the volume fraction of PANI-CSA varied by 0.1% from sample to sample. At 4.2 K, the MR increases systematically upon dilution from 100% to 1.5% PANI-CSA, whereas below 1.5% the MR de-... 

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