Physics and Astronomy Calendar

Ferromagnetic nanoparticles embedded in a semiconductor are being re-considered as prospective materials for semiconductor spintronics. They possess both good compatibility with semiconductor and high Curie temperature, which cannot be obtained by ferromagnetic semiconductor or ferromagnetic metal alone. Understanding of their spin-dependent transport characteristics is indispensable for any future applications.
GaAs:MnAs in which hexagonal (or zinc-blende) ferromagnetic MnAs nanoparticles embedded in a GaAs matrix is a well-known prototype of this kind of material. We show that hexagonal MnAs nanoparticles, when used as a ferromagnetic electrode in semiconductor based MTJ structure, can work even better than hexagonal MnAs thin film; they showed improved TMR ratio, room-temperature operation, oscillatory behaviors of TMR ratio due to quantum size effect / Coulomb Blockade effect, and so on. Very recently, we have observed an unconventionally huge magnetoresistance (MR) effect (up to 100000%) in MTJs with zinc-blende MnAs nanoparticles. Such a huge MR effect can be explained by a combination of Coulomb Blockade effect and large Zeeman splitting in zinc-blend MnAs nanoparticles. A magnetic-field dependent electromotive force emerged from those MTJs (which we call the “spin battery effect”) was also observed. Those phenomena tell us that spin-dependent transport of ferromagnetic nanoparticles embedded in a semiconductor matrix is richer than we thought.