Speaker
Description
In recent years, nanoparticles and their applications have attracted significant interest from biomedical researchers. Nanoparticles smaller than $100$ nm exhibit unique properties, including high surface-to-volume ratios, high reactivity, enhanced thermal conductivity, and tunable optical characteristics. These features make them highly useful across various fields, particularly in biomedical applications. Key applications include magnetic resonance imaging (MRI), drug or gene delivery systems, and magnetic hyperthermia, where nanoparticles serve as a heat source.
Interparticle interactions can significantly influence superparamagnetic relaxation. Furthermore, interparticle interactions can modify the spin structure of nanoparticles. An assembly of nanoparticles coupled by sufficiently weak inter-particle interactions exhibits superparamagnetic behaviour, whereas stronger interactions in densely packed systems can stabilise a superspin glass or superferromagnetic state. One of the most effective methods to gain deeper insight into the nature of these interactions and estimate their strength is the analysis of AC magnetic susceptibility.
Magnetic measurements were performed on a commercial superconducting quantum interference device (SQUID) magnetometer (Quantum Design MPMS3) in the temperature interval from $2$ K to $300$ K at various frequencies of the alternating magnetic field. The complex AC magnetic susceptibility,
$$\chi=\chi^{\prime}+\chi^{\prime\prime}$$
consists of $\chi^{\prime}$, which represents the in-phase (real) component of the AC susceptibility, and $\chi^{\prime\prime}$, which corresponds to the out-of-phase (imaginary) component. Experimental data were analysed using models that assume different strengths of interparticle interactions, including the Néel-Arrhenius and Vogel-Fulcher laws, as well as critical slowing-down analysis. The results provide an estimation of interaction strength and reveal crucial aspects of magnetic dynamics in nanoparticle systems.
Acknowledgements
This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-20-0512 and VEGA 1/0470/25.
References
[1] A. V. B. Pinheiro et al., “Exchange bias and superspin glass behavior in nanostructured CoFe2O4-Ag composites,” Journal of Magnetism and Magnetic Materials, vol. 497. Elsevier BV, p. 165940, Mar. 2020. https://doi.org/10.1016/j.jmmm.2019.165940
