Magnetic hysteresis of individual Janus particles with hemispherical exchange biased caps

Abstract

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

Dynamic Cantilever Magnetometry of Paramagnetism with Slow Relaxation

“…[27−29] Generally, the relaxation of magnetization is several orders of magnitude faster than the cantilever's oscillation. [30] Thus, at every moment of the cantilever's oscillation, magnetization has already completed the relaxation process and resides to an equilibrium position between the external magnetic field and easy axis of the sample, as illustrated in Fig. 2(a).…”