# Magnetic Force Microscopy of Micropatterned Clusters of Superparamagnetic Iron Oxide Nanoparticles

## TL;DR

Researchers used magnetic force microscopy to study the magnetic properties of patterned clusters of iron oxide nanoparticles.

## Contribution

The study reveals how magnetic interactions affect MFM measurements and how cluster geometry influences these effects.

## Key findings

- MFM phase shift from magnetic interactions was detectable at lift heights of several hundred nanometers.
- Magnetic interactions caused an apparent 'ballooning' of the feature size in MFM images.
- The results help understand how to detect SPIONs in biological environments using MFM.

## Abstract

Magnetic force microscopy (MFM) was used to characterize
micropatterned
clusters of superparamagnetic iron oxide nanoparticles (SPIONs). Top-down
lithography was used to create SPION aggregates with well-defined
geometries. The micrometer-scale aggregates exhibited different properties
from individual particles and from smaller clusters containing just
a few particles. The MFM phase shift from magnetic interactions between
the sample and probe tip could be detected at lift heights of several
hundred nanometers. The experimental data was compared to a magnetic
dipole–dipole interaction model to understand the relationship
between MFM phase shift and lift height. Magnetic interactions between
the probe tip and the sample also led to an apparent “ballooning”
of the feature size, where the aggregates appeared larger with MFM
than their physical size obtained from scanning electron microscopy.
These results can guide emerging applications of MFM, such as the
detection of SPIONs within biological environments.