Evidence for field induced proximity type behavior in CoFe2O4 based ferromagnetic nanofluid

摘要

We report some unusual magnetic properties observed in CoFe2O4 based ferrofluid (with an average particle size of D = 6 nm). More precisely, in addition to the low-field ferromagnetic (FM) phase transition with an intrinsic Curie temperature T-Cb = 350 K, a second phase transition with an extrinsic Curie temperature T-Cw = 266 K emerges at higher (saturating) magnetic field. The transitions meet at the crossover point T-cr = 210 K. The origin of the second transition is attributed to magnetic field induced proximity type interaction between FM particles through non-FM layers.