High Exchange Bias in Fe_3−δO₄@CoO Core Shell Nanoparticles Synthesized by a One-Pot Seed-Mediated Growth Method

Abstract

Core−shell nanoparticles (NPs), which consist in a ferrimagnetic (FIM)/antiferromagnetic (AFM) interface and result in exchange bias coupling, became recently of primary importance in the field of magnetic nanoparticles. The enhancement of some applications such as hyperthermia or magnetic storage media based on the miniaturization of devices is correlated to the size reduction of NPs, which results in the decrease of the magnetocrystalline anisotropy and of the blocking temperature. We present here the synthesis of Fe 3−δ O 4 @CoO core−shell NPs by a one-pot seedmediated growth process based on the thermal decomposition of metal complexes at high temperature. A 2 nm thick CoO shell was grown homogeneously from the starting Fe 3−δ O 4 core surface. The Fe 3−δ O 4 @CoO core−shell NP structure has been deeply investigated by performing XRD and advanced techniques based on TEM such as EELS and EFTEM. The high quality of the core−shell interface resulted in the large exchange bias coupling at 5 K (H E ≈ 4.1 kOe) between the FIM and the AFM components. In comparison to starting Fe 3−δ O 4 NPs, the dramatic enhancement of the magnetic properties such as a high coercive field (at 5 K, H C ≈ 15 kOe) were measured. Furthermore, the core−shell structure resulted in the enhancement of the magnetocrystalline anisotropy and the increase of the blocking temperature to 293 K.

Exploring Exchange Bias Coupling in Fe3−δO4@CoO Core–Shell Nanoparticle 2D Assemblies

“…Preparation of Azide‐Terminated Core–Shell Nanoparticles (Fe 3–δ O 4 @CoO@N 3 ) : Fe 3− δ O 4 @CoO core–shell nanoparticles were synthesized by following the exact procedure reported earlier . Iron oxide nanoparticles were synthesized first by pouring 1.38 g (2.22 mmol) of Fe(stearate) 2 , 1.254 g (4.44 mmol) of oleic acid, and 20 mL of octyl ether in a two‐necked round bottom flask.…”

Engineered inorganic core/shell nanoparticles

“…In the case of semiconductor/semiconductor or (oxyde or metal) magnetic/magnetic core/shell nanocrystals, shell growth is mainly carried out in the same high boiling point organic solvents as for the core synthesis following a seed-mediated growth approach [14,21,22]. After the core synthesis, the shell precursors are generally slowly added or fully added with a controlled amount in order to avoid homogeneous nucleation of the shell mate- [23,24,25].…”

Drug releasing nanoplatforms activated by alternating magnetic fields

“…[46] However, up to now most works were devoted to pure IONPs [23] because of their proven biocompatibility and ease of synthesis and of tuning of their size within a narrow size distribution. Despite their high potential, the development of doped ferrites was thus limited, their synthesis being generally more complex (chemical heterogeneities) [59][60][61] and their biocompatibility being discussed.…”