Structural disorder versus spin canting in monodisperse maghemite nanocrystals

Monodisperse maghemite nanoparticles with diameter ranging from 7 to 20 nm were examined by the In-field Mössbauer Spectroscopy (IFMS) in varying external magnetic field up to 6 T. Surprisingly, the small-sized particles (7 nm) exhibit nearly no spin canting in contrast to the larger particles with lower surface-to-volume ratio. We demonstrate that the observed phenomenon is originated by lower relative crystallinity of the larger particles with different internal structure. Hence, the persistence of the 2nd and 5th absorption lines in the IFMS cannot be unambiguously assigned to the surface spins.This work was supported by European Commission (MULTIFUN, No. 262943) and MSMT Project No. 7E12057. Experiments were performed in MLTL (http://mltl.eu/), which was supported within the program of Czech Research Infrastructures (Project No. LM2011025)