# Nanoscale Magnetic Compasses

## TL;DR

This paper reports the synthesis of nanoscale magnetic compasses using ferromagnetic iron carbide nanoparticles encapsulated in carbon needles, demonstrating their magnetic responsiveness and potential applications in electromagnetic materials.

## Contribution

The study introduces a novel nanoscale magnetic compass design with high yield, magnetic anisotropy, and encapsulation in a polymer matrix, advancing magnetic nanomaterial development.

## Key findings

- Nanocompasses respond to external magnetic fields.
- Magnetic fields are confined near the particles.
- The material exhibits anisotropic magnetic permeability.

## Abstract

We have synthesized nanoscale magnetic compasses with high yield. These ferromagnetic iron carbide nano-particles, which are encapsulated in a pair of parallel carbon needles, change their direction in response to an external magnetic field. Electron holography reveals magnetic fields confined to the vicinity of the bicone-shaped particles, which are composed of few ferromagnetic domains. Aligned magnetically and encapsulated in an acrylate polymer matrix, these nanocompasses exhibit anisotropic bulk magnetic permeability with an easy axis normal to the needle direction, that can be understood as a result of the anisotropic demagnetizing field of a nonspherical single-domain particle. This novel material with orthogonal magnetic and structural axes could be highly useful as magnetic components in electromagnetic wave absorbent materials and magnetorheological fluids.