Giant magnetoresistance in a low-temperature GaAs/MnAs nanoscale ferromagnet hybrid structure

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Abstract
We report the observation of a giant magnetoresistance effect in a low-temperature (LT-)GaAs/MnAs nanoscale ferromagnet hybrid structure. The MnAs nanomagnets are formed by ion implantation of Mn into LT GaAs and subsequent annealing. We have studied the magnetotransport using a vertically biased p+-GaAs/LT-GaAs:MnAs/p+-GaAs structure. A negative magnetoresistance (Δρ/ρ=[ρ(B)−ρ(0)]/ρ(0)) of up to −80% (B=7 T) is observed at low temperatures (T<20 K), which changes its sign from negative to positive between T=15 K and T=20 K. The value of the positive magnetoresistance decreases with increasing temperature from +115% (20 K) to +1.4% (300 K). The magnetoresistance variations with B and T are correlated with the nanomagnet spacing in the structure.