Magnetic coupling of iron-based ferromagnetic nanoclusters encapsulated inside double-wall carbon nanotubes

Understanding the magnetic properties of hybrids of carbon nanotubes is an intriguing matter that offers a vastly unexplored playground for fundamental research and promising applications. The magnetic properties of bundles of double-wall carbon nanotubes encapsulating cementite ferromagnetic nanoclusters (of $\sim$ 3–4 nm in length) are here studied. VSM magnetometry shows clear evidence of interparticle magnetic interactions and a large interface exchange coupling of the nanoclusters with the carbon matrix, characterized by a surface anisotropy field $H_K\sim 67$ kOe. Using a well-known measurement protocol, a magnetic activation volume for magnetization reversal was estimated as $\sim 420{\mathrm{nm}}^3$. This large volume involves around 270 cementite nanoparticles mutually coupled through the conduction electrons of the nanotubes, which provide the ground for a large magnetic correlation length, thus favoring their possible application in spintronic devices.