Interfacial spin coupling and exchange anisotropy in core–shell MnFe2O4/α-Fe2O3 nanocomposites

AbstractExchange bias properties of MnFe$$_2$$ 2 O$$_4$$ 4 @$$\gamma$$ γ –Fe$$_2$$ 2 O$$_3$$ 3 core–shell nanoparticles are investigated. The measured field and temperature dependencies of the magnetization point out a well-ordered ferrimagnetic core surrounded by a layer with spin glass-like arrangement. Quasi-static SQUID magnetization measurements are presented along with high-amplitude pulse ones and are cross-analyzed by comparison against ferromagnetic resonance experiments at 9 GHz. These measurements allow one to discern three types of magnetic anisotropies affecting the dynamics of the magnetic moment of the well-ordered ferrimagnetic NP’s core viz. the easy-axis (uniaxial) anisotropy, the unidirectional exchange-bias anisotropy and the rotatable anisotropy. The uniaxial anisotropy originates from the structural core–shell interface. The unidirectional exchange-bias anisotropy is associated with the spin-coupling at the ferrimagnetic/spin glass-like interface; it is observable only at low temperatures after a field-cooling process. The rotatable anisotropy is caused by partially-pinned spins at the core/shell interface; it manifests itself as an intrinsic field always parallel to the external applied magnetic field. The whole set of experimental results is interpreted in the framework of superparamagnetic theory, i.e., essentially taking into account the effect of thermal fluctuations on the magnetic moment of the particle core. In particular, it is found that the rotatable anisotropy of our system is of a uniaxial type.

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Ferromagnetic resonance in core-shell nanoparticles with multitype exchange anisotropy

Physical Review B ◽

10.1103/physrevb.98.014434 ◽

2018 ◽

Vol 98 (1) ◽

Cited By ~ 2

Author(s):

I. S. Poperechny ◽

Yu. L. Raikher

Keyword(s):

Ferromagnetic Resonance ◽

Core Shell ◽

Exchange Anisotropy ◽

Shell Nanoparticles ◽

Core Shell Nanoparticles

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Finding the Limits of Magnetic Hyperthermia on Core-Shell Nanoparticles Fabricated by Physical Vapor Methods

Magnetochemistry ◽

10.3390/magnetochemistry7040049 ◽

2021 ◽

Vol 7 (4) ◽

pp. 49

Author(s):

Carlos Martinez-Boubeta ◽

Konstantinos Simeonidis ◽

Judit Oró ◽

Antonios Makridis ◽

David Serantes ◽

...

Keyword(s):

Finite Size ◽

Particle Morphology ◽

Spin Coupling ◽

Core Shell ◽

Shell Nanoparticles ◽

Heating Efficiency ◽

Magnetite Fe3o4 ◽

Metal Metal ◽

Size And Morphology ◽

Core Shell Nanoparticles

Magnetic nanoparticles can generate heat when exposed to an alternating magnetic field. Their heating efficacy is governed by their magnetic properties that are in turn determined by their composition, size and morphology. Thus far, iron oxides (e.g., magnetite, Fe3O4) have been the most popular materials in use, though recently bimagnetic core-shell structures are gaining ground. Herein we present a study on the effect of particle morphology on heating efficiency. More specifically, we use zero waste impact methods for the synthesis of metal/metal oxide Fe/Fe3O4 nanoparticles in both spherical and cubic shapes, which present an interesting venue for understanding how spin coupling across interfaces and also finite size effects may influence the magnetic response. We show that these particles can generate sufficient heat (hundreds of watts per gram) to drive hyperthermia applications, whereas faceted nanoparticles demonstrate superior heating capabilities than spherical nanoparticles of similar size.

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Tailoring Interfacial Exchange Anisotropy in Hard–Soft Core-Shell Ferrite Nanoparticles for Magnetic Hyperthermia Applications

Nanomaterials ◽

10.3390/nano12020262 ◽

2022 ◽

Vol 12 (2) ◽

pp. 262

Author(s):

Venkatesha Narayanaswamy ◽

Imaddin A. Al-Omari ◽

Aleksandr S. Kamzin ◽

Bashar Issa ◽

Ihab M. Obaidat

Keyword(s):

Magnetic Hyperthermia ◽

Ferrite Nanoparticles ◽

Soft Core ◽

Core Shell ◽

Zero Field ◽

Exchange Anisotropy ◽

Shell Nanoparticles ◽

Heating Efficiency ◽

Two Samples ◽

Core Shell Nanoparticles

Magnetically hard–soft core-shell ferrite nanoparticles are synthesized using an organometallic decomposition method through seed-mediated growth. Two sets of core-shell nanoparticles (S1 and S2) with different shell (Fe3O4) thicknesses and similar core (CoFe2O4) sizes are obtained by varying the initial quantities of seed nanoparticles of size 6.0 ± 1.0 nm. The nanoparticles synthesized have average sizes of 9.5 ± 1.1 (S1) and 12.2 ± 1.7 (S2) nm with corresponding shell thicknesses of 3.5 and 6.1 nm. Magnetic properties are investigated under field-cooled and zero-field-cooled conditions at several temperatures and field cooling values. Magnetic heating efficiency for magnetic hyperthermia applications is investigated by measuring the specific absorption rate (SAR) in alternating magnetic fields at several field strengths and frequencies. The exchange bias is found to have a nonmonotonic and oscillatory relationship with temperature at all fields. SAR values of both core-shell samples are found to be considerably larger than that of the single-phase bare core particles. The effective anisotropy and SAR values are found to be larger in S2 than those in S1. However, the saturation magnetization displays the opposite behavior. These results are attributed to the occurrence of spin-glass regions at the core-shell interface of different amounts in the two samples. The novel outcome is that the interfacial exchange anisotropy of core-shell nanoparticles can be tailored to produce large effective magnetic anisotropy and thus large SAR values.

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Role of Frozen Spins in the Exchange Anisotropy of Core−Shell Fe@Fe3O4 Nanoparticles

The Journal of Physical Chemistry C ◽

10.1021/jp110716g ◽

2011 ◽

Vol 115 (6) ◽

pp. 2665-2672 ◽

Cited By ~ 56

Author(s):

Quy Khac Ong ◽

Xiao-Min Lin ◽

Alexander Wei

Keyword(s):

Fe3o4 Nanoparticles ◽

Core Shell ◽

Exchange Anisotropy

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A crystalline–amorphous Ni–Ni(OH)2 core–shell catalyst for the alkaline hydrogen evolution reaction

Journal of Materials Chemistry A ◽

10.1039/d0ta08735a ◽

2020 ◽

Vol 8 (44) ◽

pp. 23323-23329

Author(s):

Jing Hu ◽

Siwei Li ◽

Yuzhi Li ◽

Jing Wang ◽

Yunchen Du ◽

...

Keyword(s):

Hydrogen Evolution ◽

Hydrogen Evolution Reaction ◽

Electrocatalytic Activity ◽

Core Shell ◽

Alkaline Conditions

Crystalline–amorphous Ni–Ni(OH)2 core–shell assembled nanosheets exhibit outstanding electrocatalytic activity and stability for hydrogen evolution under alkaline conditions.

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