Abstract
In this work a full angle dependent Ferromagnetic Resonance (FMR) investigation on a system of 20 separated Fe/FexOy nanocubes without dipolar coupling is reported. The angular magnetic field dependence of FMR spectra of 20 single particles and 2 dimers were recorded using a microresonator setup with a sensitivity of 106 μB at X-band frequencies. We determine an effective magnetocrystalline anisotropy field of 2K4,eff/M = 50 mT ± 5 mT for selected particles, which is smaller than the one of bulk Fe due to the core shell morphology of the particles. The FMR resonances have a linewidth of 4 mT ± 1 mT, corresponding to a magnetic effective damping parameter α = 0.0045 ± 0.0005 matching the values of high quality iron thin films. Numerical calculations taking into account the different angular orientations of the 24 particles with respect to the external magnetic field yield a good agreement to the experiment.
Highlights
Magnetic nanoparticles have been extensively studied with various techniques over the last decades
The Ferromagnetic Resonance (FMR) resonances have a linewidth of 4 mT ± 1 mT, corresponding to a magnetic effective damping parameter α = 0.0045 ± 0.0005 matching the values of high quality iron thin films
Numerical calculations taking into account the different angular orientations of the 24 particles with respect to the external magnetic field yield a good agreement to the experiment
Summary
Magnetic nanoparticles have been extensively studied with various techniques over the last decades (see Refs. 1–4 and references therein). While static hysteresis loop measurements of single nanocubes with 20 nm side length have been reported recently[5] measurements of the magnetic anisotropy and relaxation of single, uncoupled nanoparticles (less than 30 nm) by ferromagnetic resonance have not been reported yet. Conventional measurement FMR setups using microwave cavities are unable to detect single nanoparticles due to the insufficient sensitivity. A solution for this problem is the use of planar microresonator (PMR) structures, which offer the possibility to detect 106 μB.[6,7] This magnetic moment per particle roughly corresponds to a cubic shaped particle with an edge length of 30 nm.[8,9] Here, we report on the magnetic characterization of single uncoupled iron/iron oxide core shell nanoparticles in different configurations by FMR at room temperature. Numerical calculations are found to be in good agreement with our experiment
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