We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature TC can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x=20%. The temperature Tm, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below TC, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than Tm.
Tunneling magnetoresistance ͑TMR͒ in Ga 0.92 Mn 0.08 As/ Al-O / Co 40 Fe 40 B 20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field ͉H͉ Յ 2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 A. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented.
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