Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy

Abstract

Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10−20 A m2, respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution.

Magnetic Colloidal Particles in Combinatorial Thin-Film Gradients for Magnetic Resonance Imaging and Hyperthermia

“…In each section of bilayers, agglomeration of particles in the form of clusters 9 Advances in Polymer Technology was successfully imaged. From the MFM images, one can see the phase shift in terms of degrees resulting from the tip and sample interactions [49]. As the number of adsorbed colloids increases with the number of bilayers, there can be an increase in the interaction between the tip and the substrate that causes the shift in the oscillation of the cantilever.…”

Magnetic properties of individual Co2FeGa Heusler nanoparticles studied at room temperature by a highly sensitive co-resonant cantilever sensor

“…In order to successfully explore and employ the magnetic nanoparticles for the applications, a thorough characterization of their magnetic properties is essential. Several techniques are available for this purpose, for example SQUIDs 11 – 16 , magnetometers based on air coils driven by an alternating current or the Hall effect 17 – 19 , magnetic force microscopy-based methods 20 , 21 , cantilever magnetometry 22 – 25 , spinpolarized scanning tunnelling microscopy 26 , 27 , magnetometry based on nitrogen-vacancy defects 28 and electron holography 1 , 29 . These techniques have been employed to study magnetization reversal processes in nanoparticles induced by current 26 , 27 or by an external magnetic field 12 , 21 , 22 and to investigate the magnetic stray fields of nanoparticles 1 , 29 .…”

“…The challenge for all experimental techniques lies in the nanometer size of the particles and the corresponding weak magnetic signals. Therefore, the measurement setups have to be very complex to reach the required sensitivity or spatial resolution, respectively 20 . This might be achieved by reducing the sensor’s dimensions 12 , 22 , and by employing low temperatures 11 , 21 .…”

pH Tunable Thin Film Gradients of Magnetic Polymer Colloids for MRI Diagnostics

“…As the number of particles deposited increases as in sample D, bright features become more prominent. The samples with few particles like samples A and B have less interaction with the tip, thus agglomerates behave as single dipoles [ 53 ]. Sample C has a contrast between samples B and D. The nonlinear deposition of magnetic colloids when a number of bilayers are small was due to the dominant interaction between substrate and polycation.…”