Synthetic antiferromagnetic nanoplatelets (NPs) with perpendicular magnetic anisotropy (PMA) are promising candidates for nano-torque-related applications 1. To manipulate the NPs, a good understanding of the homogeneity in magnetic and structural properties is required. Most techniques measure these properties based on ensemble techniques 2, however, an efficient and easy magnetic characterization technique on single particle level, down to the nanometer range, is currently lacking. Here, we present a characterization method based on photothermal magnetic circular dichroism (PT MCD), which measures the differential absorption of left and right circularly polarized light of an individual magnetic nanoparticle due to the polar Kerr effect 3. In this way the hysteresis loop on a single 120 nm diameter SAF NP is obtained (see Fig 1b). When compared to SQUID (of ~106 particles) as shown in Fig. 1c, the loop exhibits comparable behavior i.e., the antiferromagnetic state at zero applied field and a sharp magnetization switch at a large field. We notice that the values of the switching fields (BL and BH as schematically represented in Fig. 1b) are different from the SQUID measurement, which is due to the increased temperature of the NP during the PT MCD measurement. The statistics of the switching fields by PT MCD are shown in Fig 1d where a difference in the distribution is observed for the BH and BL switch, which we attribute to a change in the dominant magnetic reversal mechanism of the NPs 4. Our results will pave the way to a deeper understanding of torque based applications using PMA-SAF NPs and introduce the PT MCD method to the magnetic-nanoparticle community 5.

References:

1 Mansell, R., et al. Scientific reports 7.1 (2017): 1-7.
2 Wasielewski, M. R., et al. Nature Reviews Chemistry 4.9 (2020): 490-504.
3 Spaeth, Patrick, et al. Nano letters 22.9 (2022): 3645-3650.
4 Thomson, T., et al. Physical review letters 96.25 (2006): 257204.
5 Adhikari, S, Li, J., et al. In-Preparation (2022)