Performing magnetization studies on individual nanoparticles is a highly demanding task, especially when measurements need to be carried out under large sweeping magnetic fields or variable temperature. Yet, characterization under varying ambient conditions is paramount in order to fully understand the magnetic behavior of these objects, e.g., the formation of non-uniform states, the mechanisms leading to magnetization reversal, thermal stability or damping processes. This, in turn, is necessary for the integration of magnetic nanoparticles and nanowires into useful devices, e.g., spin-valves, racetrack memories or magnetic tip probes. Here we show that YBa2Cu3O7 nano Superconducting QUantum Interference Devices (YBCO nanoSQUIDs, see Fig.) are particularly well suited for this task. We have successfully characterized a number of individual nanoparticles of soft magnetic materials with different shapes (nanodots, nanodiscs and nanowires, see Figure). Samples are transported to the surface of the sensor with nanometric resolution, achieving sufficiently strong particle-SQUID coupling. Magnetization measurements (see Figure) performed under sweeping magnetic fields (up to ~ 500 mT) and variable temperature (1.4 - 80 K) underscore the intrinsic differences between samples owing to their shape and the presence (or absence) of magnetocrystalline anisotropy. Our measurements also allow us to distinguish the mechanisms leading to magnetization reversal mediated by, i.e., nucleation/propagation of domain walls or nucleation/annihilation of magnetic vortices. These studies serve to shed light on the nature and magnitude of the energy barriers separating different magnetic states, nucleation/annihilation fields and switching times.

Multi-shaped individual nanoparticles investigated by nanoSQUID magnetometry at variable temperature INVITED

E2: Nanoparticle and Nanowire Arrays and Self-assembly

technical paper

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

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Maria Jose Martinez-Perez

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Multi-shaped individual nanoparticles investigated by nanoSQUID magnetometry at variable temperature INVITED

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