Time-Resolved Diamond Magnetic Microscopy of Superparamagnetic Iron-Oxide Nanoparticles
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-03-07 |
| Journal | ACS Nano |
| Authors | Bryan A. Richards, Nathaniel Ristoff, Jānis Šmits, A. Pérez, Ilja Fescenko |
| Institutions | Oak Ridge National Laboratory, MMR Technologies (United States) |
| Citations | 3 |
| Analysis | Full AI Review Included |
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View Original Abstract
Superparamagnetic iron-oxide nanoparticles (SPIONs) are promising probes for biomedical imaging, but the heterogeneity of their magnetic properties is difficult to characterize with existing methods. Here, we perform wide-field imaging of the stray magnetic fields produced by hundreds of isolated ∼30 nm SPIONs using a magnetic microscope based on nitrogen-vacancy centers in diamond. By analyzing the SPION magnetic field patterns as a function of the applied magnetic field, we observe substantial field-dependent transverse magnetization components that are typically obscured with ensemble characterization methods. We found negligible hysteresis in each of the three magnetization components for nearly all SPIONs in our sample. Most SPIONs exhibit a sharp Langevin saturation curve, enumerated by a characteristic polarizing applied field, <i>B</i><sub>c</sub>. The <i>B</i><sub>c</sub> distribution is highly asymmetric, with a standard deviation (σ<sub>c</sub> = 1.4 mT) that is larger than the median (0.6 mT). Using time-resolved magnetic microscopy, we directly record SPION Néel relaxation, after switching off a 31 mT applied field, with a temporal resolution of ∼60 ms, which is limited by the ring-down time of the electromagnet coils. For small bias fields |<i>B</i><sub>hold</sub>| = 1.5-3.5 mT, we observe a broad range of SPION Néel relaxation times - from milliseconds to seconds - that are consistent with an exponential dependence on <i>B</i><sub>hold</sub>. Our time-resolved diamond magnetic microscopy study reveals rich SPION sample heterogeneity and may be extended to other fundamental studies of nanomagnetism.