Magnetic properties of nanoscale crystalline maghemite obtained by a new synthetic route

In this work we describe the synthesis and characterization of maghemite nanoparticles obtained by a new synthetic route. The material was synthesized using triethylamine as a coprecipitation agent in the presence of the organic ligand N , N′ -bis(3,5-di-tert-butyl-catechol)-2,4-diaminotoluene (LCH 3 ). Mossbauer spectrum at 4 K shows typical hyperfine parameters of maghemite and Transmission Electron Microscopy images reveal that the nanoparticles have a mean diameter of 3.9 nm and a narrow size distribution. AC magnetic susceptibility in zero field presents an Arrhenius behavior with unreasonable relaxation parameters due to the strong influence of dipolar interaction. In contrast when the measurements are performed in a 1 kOe field, the effect of dipolar interactions becomes negligible and the obtained parameters are in good agreement with the static magnetic properties. The dynamic energy barrier obtained from the AC susceptibility results is larger than the expected from the average size observed by HRTEM results, evidencing the strong influence of the surface contribution to the anisotropy.