Interplay between exchange interaction and magnetic anisotropy for iron based nanoparticles in aligned carbon nanotube arrays

In this work, we investigate magnetic properties of iron based nanoparticles (NP) intercalated into carbon nanotube (CNT) aligned arrays synthesized by injection chemical vapor deposition. We have analyzed the temperature (T) and the ferrocene concentration (CF) dependences of the macroscopic magnetic parameters. From these experiments a weaker interaction between magnetic moments of NP was obtained for low CF values. The random anisotropy model for the experimental data analysis was applied and micromagnetic parameters were evaluated. The law of the approach to magnetic saturation (LAS) was analyzed using the general expression with the correlation function C(r = x/Ra) of magnetic axes, Ra being the magnetic anisotropy correlation length. We obtained that, while for CF = 0.5% C(r) is a step-like (C(r < 10) = 1, C(r > 10) = 0), for CF ⩾ 1% C(r) decays rapidly on a short range, (2-3)Ra. Such extended correlations for CF = 0.5% could be associated with the dominant role of the coherent anisotropy, which is caused by the influence of the alignment of CNT. When the aligned CNTs for CF = 0.5% are destroyed into powder, the LAS is changed to H−1/2, which means the dominant role of the exchange mechanism.