Multiple magnetic characteristics in pure and Mn porphyrin-doped single-walled carbon nanotubes

Abstract

Magnetism of single-walled carbon nanotubes (SWCNT) is probed and an unexpected multiple magnetic behavior is observed. Paramagnetism, diamagnetism, and ferro(antiferro)magnetism in superparamagnetic form are present in 99.9 % pure samples. A paramagnetic component and a diamagnetic component, both present in the whole magnetic field range, add up to form a net diamagnetism, as expected. Moreover, antiferromagnetism is present. By contrast, a Mn(III)-porphyrin/SWCNT nanocomposite shows a different behavior. The SWCNT net diamagnetism vanishes, and spin-glass (spin-canted) behavior is observed. A de Almeida–Thouless line fit is used to verify the existence of the spin-glass state. Thermogravimetric analysis, along with electron spin resonance and energy dispersive spectrometry indicates that the amount of residual catalyst nanoparticles <1 % wt. left from the synthesis of SWCNT is unable to explain the magnetic behavior observed. Theoretical works are used to explain the phenomena.