Magnetoresistance due to inelastic spin-flip cotunneling within Coulomb blockade regime in III-V semiconductor / MnAs nanoparticle heterostructures

Inelastic spin-flip cotunneling is a key to understand the spin-dependent single-electron transport in the ferromagnetic nanoparticles systems. We fabricated a heterostructure consisting of Al/ AlAs/ ferromagnetic zinc-blende (ZB) MnAs nanoparticles embedded in GaAs / GaAs:Be on a GaAs(001) substrate, where electrons are expected to go through only one nanoparticle during tunneling. By analyzing the $I-V$ data at various temperatures $T$, we found that inelastic cotunneling is dominant when $T<$60 K. The ratio of the inelastic cotunneling energy $E$ to the thermal energy \textit{kT}, estimated by the $I-V$ data, was remarkably increased with decreasing $T$. We observed clear magnetoresistance (MR) up to $\sim $3{\%} (at 1T), and MR was also increased with decreasing $T$. The shape of the \textit{MR-T }curve was quite similar to that of the \textit{E/kT - T} curve, which strongly suggests that MR is induced by the spin-flip process due to inelastic cotunneling. From the \textit{E/kT - T} curve, the energy needed for the spin-flip process is estimated to be $\sim $0.04 meV, which corresponds to $\sim $3.3{\%} of the inelastic cotunneling energy. This work was partly supported by the Grant-in-Aids for Scientific Research, Special Coordination Programs by JST, FIRST Program, and JSPS Fellowship.