  In this paper, we propose a compact integrated hybrid plasmonic-photonic
device for optical reading of nanoscale magnetic bits with perpendicular
magnetic anisotropy in a magnetic racetrack on top of a photonic waveguide on
the indium phosphide membrane on silicon platform. The hybrid device is
constructed by coupling a doublet of V-shaped gold plasmonic nanoantennas on
top of the indium phosphide waveguide. By taking advantage of the localized
surface plasmons, our hybrid device can enable detection of the magnetization
state in magnetic bits beyond the diffraction limit of light and enhance the
polar magneto-optical Kerr effect (PMOKE). We further illustrate how combining
the hybrid device with a plasmonic polarization rotator provides
magneto-optical read-out by transforming the PMOKE-induced polarization change
into an intensity variation of the waveguide mode. According to the simulation
results based on a three-dimensional finite-difference time-domain method, the
hybrid device can detect the magnetization states in targeted bits in a
magnetic racetrack medium down to ~ 100x100 nm2, regardless of the
magnetization state of the rest of the racetrack with a relative intensity
contrast of greater than 0.5% for a ~ 200x100 nm2 magnetic bit. We believe our
hybrid device can be an enabling technology that can connect integrated
photonics with nanoscale spintronics, paving the way toward ultrafast and
energy efficient advanced on-chip applications.
