M. Sakuma

Nanoscale magnet for semiconductor spintronics

A hybrid nanostructure of diluted magnetic semiconductor quantum well (DMS-QW) has been fabricated by using a ferromagnetic Co∕Pt-multilayered film with perpendicular magnetization. The nanoscale disk of DMS-QW with a diameter of 80nm was embedded in the magnetic film generating magnetic fields perpendicular to the DMS-QW plane. As a result, exciton photoluminescence with circular-polarization properties arises in a zero external field, due to the giant Zeeman effects of excitons. It indicates that the perpendicular magnetic fields applied from the Co∕Pt film align the exciton spins in the DMS nanoscale disk, acting as a nanoscale magnet for semiconductor spintronics.

Giant Zeeman effect of excitons in a hybrid nanostructure of diluted magnetic semiconductor quantum well sandwiched in Co wires

Giant Zeeman effects of excitons in a hybrid nanostructure of diluted magnetic semiconductor (DMS) quantum well (QW) with ferromagnetic Co have been demonstrated, where the DMS-QW wire with the width of 200 nm is sandwiched in the Co wires and magnetic fields nearly perpendicular to the well plane can efficiently be applied from the Co wires to all of the DMS QW. The spectral shape of excitonic photoluminescence and the field dependence show clearly that the microscopic perpendicular fields generated from the Co wires induce the giant Zeeman shifts of excitons in the DMS QW.

Fabrication and magnetooptical properties of nanostructures of diluted magnetic semiconductors integrated with glass thin films

We have fabricated nanostructures of diluted magnetic semiconductors (DMSs) integrated with high-purity glass thin films and have studied the giant magneto-optical properties, for the purpose of applying in microscopic magneto-optical devices. Zn1-x-yCdxMnySe quantum wells grown on GaAs substrates were fabricated into two-dimensional arrays of disks or wires with the lateral dimensions ranging from 10 to 500 nm using electron-beam lithography. These nanostructures have been covered with SiO2 thin films, without a significant degradation of their optical quality, by ultrahigh vacuum sputtering with low plasma damage. The giant Zeeman effects of excitonic photoluminescence (PL) in the integrated nanostructures of DMS are studied in terms of the exchange interactions between exciton and magnetic ions. The magnetic-field dependence of the giant Zeeman shift of excitons shows a redshift beyond 25 meV for 5 T with a significant increase in PL intensity. This ensures characteristic magneto-optical functionalities of the present integrated nano-glass structures of DMS.

Dynamic magnetic properties of epitaxial MnAs thin films studied by spin-wave Brillouin scattering

Dynamic magnetic properties of epitaxial MnAs thin films are studied by means of Brillouin light scattering (BLS). The sharp spectral peaks of the inelastic BLS are observed in room temperature, which are attributed to surface spin waves indicating the long-wavelength collective behavior of ferromagnetic spins. The field dependence of the surface spin-wave frequency is strongly affected by an in-plane angle between the crystal axis and the external field direction in a GaAs(100)/MnAs(-1100) film, which originates from uniaxial magnetic anisotropy parallel to the MnAs[11-20] axis and the modified g value. Significant damping of the spin-wave BLS spectrum is observed with increasing excitation laser power, possibly due to thermal effects.