Evidence for field induced proximity type behavior in ferromagnetic nanofluid

TL;DR

This study reveals unusual magnetic phase transitions in CoFe2O4 nanofluids, including a field-induced proximity interaction causing a second ferromagnetic transition at lower temperature.

Contribution

The paper reports the discovery of a field-induced proximity type behavior in ferromagnetic nanofluids, highlighting a novel magnetic interaction mechanism.

Findings

Identification of two distinct Curie temperatures in the nanofluid.

Observation of a field-induced second ferromagnetic transition.

Evidence of proximity interaction between FM particles.

Abstract

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=350K, a second phase transition with an extrinsic Curie temperature T_Cw = 266K 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.