Magnetic hysteresis of individual Janus particles with hemispherical exchange biased caps

We use sensitive dynamic cantilever magnetometry to measure the magnetic hysteresis of individual Janus particles. These particles consist hemispherical caps material deposited on micrometer-scale silica spheres. The measurements, combined with corresponding micromagnetic simulations, reveal configurations present in these curved magnets. In remanence, ferromagnetic are found host a global vortex state vanishing moment. contrast, remanent onion significant moment is recovered by imposing an exchange bias system via additional antiferromagnetic layer cap. A robust crucial for most applications particles, which external field actuates their motion.