On the magnetic anisotropy and nuclear relaxivity effects of Co and Ni doping in iron oxide nanoparticles

Abstract

We report a systematic experimental study of the evolution of the magnetic and relaxometric properties as a function of metal (Co, Ni) doping in iron oxide nanoparticles. A set of five samples, having the same size and ranging from stoichiometric cobalt ferrite (CoFe 2 O 4) to stoichiometric nickel ferrite (NiFe 2 O 4) with intermediate doping steps, was ad hoc synthesized. Using both DC and AC susceptibility measurements, the evolution of the magnetic anisotropy depending on the doping is qualitatively discussed. In particular, we observed that the height of the magnetic anisotropy barrier is directly proportional to the amount of Co, while the Ni has an opposite effect. By Nuclear Magnetic Resonance Dispersion (NMR-D) experiments, the experimental longitudinal r 1 and transverse r 2 relaxivity profiles were obtained, and the heuristic theory of Roch et al. was used to analyze the data of both r 1 and, for the first time, r 2. While the experimental and fitting results obtained from r 1 profiles were satisfying and confirmed the anisotropy trend, the model applied to r 2 hardly explains the experimental findings. V

Optimized PAMAM coated magnetic nanoparticles for simultaneous hyperthermic treatment and contrast enhanced MRI diagnosis

“…3B, solid lines). A similar mismatch has previously been observed 26,27 and attributed to one or more physical mechanisms not included in the model itself. On this respect, it should be observed that the RMG model describes systems in the so called motional averaging regime (in short MAR, corresponding to fast motions) while our systems are out of the limit of the MAR regime.…”

Local spin dynamics of iron oxide magnetic nanoparticles dispersed in different solvents with variable size and shape: A 1H NMR study

“…[27][28][29] It should be noticed that this model presents serious limits for the exact quantitative estimation of E B , but allows us to grasp its general trend as a function of size, shape, and dispersant. 32 On the other hand, no model able to predict the ZFC curve behavior of interacting MNPs is actually widely accepted in the literature, 30 thus preventing us to use a more refined theory for the E B evaluation. The ZFC data were fitted by using the formula…”

Coating Effect on the 1H—NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles

“…The efficiency of such particles for diagnostics has indeed been demonstrated to depend on several magnetic (nature of metal ion, spin topology, magnetic anisotropy), morphological/structural (core diameter, shape, crystallinity degree, coating thickness) and chemical (water exchange dynamics, principally due to coating hydrophilicity, permeability and thickness) parameters [ 21 , 22 , 23 , 24 , 25 , 26 ]. Moreover, a great potential of MNPs relies on their reactive surface, which can be exploited for the anchorage of several molecules with different functionalities.…”