The stress, surface spin and dipolar interaction in the diluted NiFe2O4 nanoparticles by the SiO2 matrix: Characterization and analyses

Well-dispersed uniform NiFe2O4 nanoparticles (NPs) with an average particle size of 15.4 nm were synthesized by thermal decomposition of a metal-organic salt, and then were diluted in a SiO2 matrix via a sol-gel method with different concentration. The magnetization (M) dependence of NiFe2O4/SiO2 on the temperature (T) and on the applied magnetic field (H) was systematically characterized by the Quantum Design superconducting quantum interference device (SQUID) PPMS system. The results of M similar to H/T divide the magnetic properties between 10 K and 300 K into two regions: the low temperature blocked-particle regime below the blocking temperature T-B and the interacting superparamagnetic (ISP) regime above T-B. In the ISP regime, all samples deviate from the ideal Langevin superparamagnetic behavior due to the effective anisotropy induced by the stress, surface spins and interparticle dipolar interaction. The Raman spectra indicate that the stress in all samples exhibits the vibration behavior, which leads to the effective anisotropy and hence coercivity vibration. (C) 2015 Elsevier Inc. All rights reserved.