  Manipulation of the magnetization by external energies other than magnetic
field, such as spin-polarized current1-4, electric voltage5,6 and circularly
polarized light7-11 gives a paradigm shift in magnetic nanodevices.
Magnetization control of ferromagnetic materials only by circularly polarized
light has received increasing attention both as a fundamental probe of the
interactions of light and magnetism but also for future high-density magnetic
recording technologies. Here we show that for granular FePt films, designed for
ultrahigh-density recording, the optical magnetic switching by circularly
polarized light is an accumulative effect from multiple optical pulses. We
further show that deterministic switching of high anisotropy materials by the
combination of circularly polarized light and modest external magnetic fields,
thus revealing a pathway towards technological implementation.
