Magnetic hysteresis of individual Janus particles with hemispherical exchange-biased caps

TL;DR

This study measures the magnetic hysteresis of individual Janus particles with hemispherical caps, revealing their magnetic configurations and how exchange bias influences their remanent magnetic states, which is vital for applications involving magnetic actuation.

Contribution

It introduces sensitive dynamic cantilever magnetometry combined with micromagnetic simulations to analyze magnetic configurations of individual Janus particles with exchange bias.

Findings

Ferromagnetic Janus particles host a vortex state with zero magnetic moment in remanence.

Applying exchange bias induces a remanent onion state with a significant magnetic moment.

The magnetic state can be controlled by exchange bias, impacting their actuation capabilities.

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.