# Deformation of flexible ferromagnetic filaments under a rotating magnetic field

## TL;DR

This paper experimentally studies how ferromagnetic filaments deform under a rotating magnetic field, revealing dependencies on filament length, magnetic field strength, and frequency, with implications for bio-sensing applications.

## Contribution

It provides new experimental insights into the deformation behavior of ferromagnetic filaments under rotating magnetic fields, including how deformation varies with physical and magnetic parameters.

## Key findings

- Longer filaments deform more under the same conditions.
- Filament angle increases linearly with frequency at low frequencies.
- High frequencies cause filaments to move out of plane.

## Abstract

Research on magnetic particles dispersed in a fluid medium, actuated by a rotating magnetic field, is becoming increasingly active for both lab-on-chip and bio-sensing applications. In this study, we experimentally investigate the behaviour of ferromagnetic filaments in a rotating field. Filaments are synthesized by linking micron-sized ferromagnetic particles with DNA strands. The experiments were conducted under different magnetic field strengths, frequencies and filament sizes, and deformation of the filaments was registered via microscope and camera. The results obtained showed that the body deformation is larger for longer filaments and higher frequencies and lower for larger magnetic field. The angle between the filament tangent at the centre and the magnetic field direction increases linearly with frequency at low-frequency regime. A further increase in the frequency will result in filament movement out of plane when the angle approaches 90 degrees. The experimental results were used to estimate magnetic moment and the bending elasticity of the filament.