  We present an integrated magneto-photonic device for all-optical switching of
non-volatile multi-bit spintronic memory. The bits are based on stand-alone
magneto-tunnel junctions which are perpendicularly magnetized with
all-optically switchable free layers, coupled onto photonic crystal nanobeam
cavities on an indium phosphide based platform. This device enables switching
of the magnetization state of the bits by locally increasing the power
absorption of light at resonance with the cavity. We design an add/drop network
of cavities to grant random access to multiple bits via a wavelength-division
multiplexing scheme. Based on a three-dimensional finite-difference time-domain
method, we numerically illustrate a compact device capable of switching and
accessing 8 bits in different cavities with a 5 nm wavelength spacing in the
conventional (C) telecommunication band. Our multi-bit device holds promise as
a new paradigm for developing an ultrafast photonically-addressable spintronic
memory and may also empower novel opportunities for photonically-driven
spintronic-based neuromorphic computing.
