Probing core and shell contributions to exchange bias in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Co</mml:mi><mml:mo>/</mml:mo><mml:msub><mml:mi>Co</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>nanoparticles of controlled size

De, D.; Iglesias, Òscar; Majumdar, S.; Giri, S.

doi:10.1103/physrevb.94.184410

Cited by 25 publications

(18 citation statements)

References 59 publications

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“…Third, the crystallized Co@CoO nanoparticles of the core–shell structure is proved by high-resolution TEM figures presented in Figure f, as indexed by the interplanar distance of the (002) reflection in Co (0.199 nm) and the (200) reflection in CoO (0.232 nm), respectively. As shown by the blue line, the core–shell Co@CoO nanoparticles are similar to previously reported cases. , …”

Section: Resultssupporting

confidence: 89%

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

Tian

Zhao

et al. 2021

J. Phys. Chem. C

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In this paper, crystallized core–shell Co@CoO nanocluster assembled thin films with different thicknesses were prepared by magnetron sputtering. A large zero-field-cooled exchange bias (ZEB) around 1280 Oe was obtained in the Co–CoO film with a thickness of 18 nm at 10 K. This phenomenon is mainly due to the formation of oriented Co@CoO core–shell nanoclusters (Co along the easy magnetization axis) in the amorphous Co–CoO matrix, thus exhibiting remnant magnetization, which is responsible for the ZEB. Moreover, the ZEB effect can be tuned by the varying film thickness. When the film thickness is decreased or increased, ZEB becomes weak, even vanishes. This indicates that we can select the desired value of ZEB via a simple control of the film thickness, which will benefit the applications of these thin films in the magnetic industry.

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Section: Resultssupporting

confidence: 89%

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

Tian

Zhao

et al. 2021

J. Phys. Chem. C

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“…This exchange bias continues up to the T B (∼345 K) although Co 3 O 4 (shell) has a much lower ordering temperature. This result is consistent with what has been found at the interface of the Co 3 O 4 (shell)–Co (core) nanoparticles with different phase fractions . These results show that the robustness of the exchange coupling between the Co (core) and Co 3 O 4 (shell) nanowires and the persistence of the exchange bias effect persist up to room temperature.…”

Section: Resultssupporting

confidence: 59%

High-Coercivity Cobalt Nanowire Arrays: Synthesis and Heat Treatment

Xu,

Yao,

Lou

et al. 2023

Crystal Growth & Design

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An anodic aluminum oxide (AAO) template with a highly ordered structure is prepared and used for the synthesis of Co nanowire arrays. The surface of Co nanowires is smooth and uniform, the diameter is 50 nm, the length is about 20 μm, and the aspect ratio of a Co nanowire is about 400. A large aspect ratio represents a strong shape anisotropy and dipolar interactions, resulting in high coercivity. In addition, the small diameter of the nanowires also contributes to the increased coercivity because the small size hinders the propagation mechanism of the domain walls during magnetic inversion. The magnetic curve in the parallel configuration shows a higher coercivity and remanence than that in the perpendicular configuration, and the rectangle is also more obvious. The shape anisotropy of nanowires tends to be magnetized along the axis, so an easy magnetization axis is parallel to nanowires. In order to investigate the effect of heat treatment on the magnetic properties of nanowires, we treated the samples for different times. The Co 3 O 4 (shell)−Co (core) structure was formed after the surface oxidation of the annealed Co nanowires. The grain size and diameter after heat treatment are twice as large as those without treatment; the thickness of the shell is about 25 nm, and the diameter of the core is about 50 nm. The core−shell interface is clearly distinguishable with increasing roughness. Due to the coexistence of two phases and the increase in grain size, the saturated magnetic moments decrease, and the coercivity and remanence ratio increase with the increase of heat treatment time. There is an exchange interaction between the core and shell magnetic phases, and the magnetic signal is a result of the competing ferromagnetic core and antiferromagnetic shell. The Co 3 O 4 (shell)−Co (core) nanowires are basically in the ferromagnetic state, the coercivity is twice that of Co showing a large magnetocrystalline anisotropy and energy, and the direction parallel to the nanowire axis is easier to be magnetized. The exchange bias effect can persist up to above room temperature, which is directed by the interfacial spin pinning effect, and the coercivity and the shift of the hysteresis loop depend on the contribution of the interfacial surface spins to the magnetization reversal.

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“…Note that measured value of µ 0 H E = 365 mT on the composite particles is significantly higher than the best values recently reported on oxide‐based granular composites called “giant exchange‐bias” systems, like NiFe 2 O 4 ‐CoO, SrFe 12 O 19 @CoO, CoFe 2 O 4 @Co 3 O 4, and others summarized in Table SI‐1 in the Supporting Information. These results are very promising and make our engineered CFO‐CO composites particularly valuable as starting powder for the production of exchange‐biased oxide‐based consolidates.…”

Section: Resultsmentioning

confidence: 56%

Giant Exchange‐Bias in Polyol‐Made CoFe₂O₄‐CoO Core–Shell Like Nanoparticles

Flores‐Martínez

Franceschin

Gaudisson

et al. 2018

Part & Part Syst Charact

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Cobalt ferrite ferrimagnetic nanoparticles (NPs) are prepared and used in this work as seeds to grow a thin antiferromagnetic poly‐ and nanocrystalline CoO shell. The major purpose is to study systematically the characteristics of the as‐produced powders, making emphasis on their internal crystallographic arrangement and their magnetic properties. 57Fe Mössbauer spectrometry evidences an evolution of the cation distribution among the spinel lattice in the cobalt ferrite core during the core–shell NPs processing. High‐resolution transmission electron microscopy shows a perfect epitaxy between the face‐centered cubic lattices of the spinel core and the rock‐salt shell. Finally, the measurements of 7T‐field‐cooled magnetic hysteresis loops at low temperature (5 K) of the composite particles exhibit a strong exchange bias coupling with an exchange field, µ0HE, of 365 mT and an enhanced coercive field, µ0HC, of 1395 mT. These values are very high compared to those of differently prepared CoO‐based oxide composite NPs and for which a giant exchange‐bias is reported. These features are attributed to the favorable material processing conditions offered by the polyol process in terms of crystalline quality, particularly at the interfaces, and for the pinning action exerted by the CoO phase on the magnetization of the CoFe2O4 phase.

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Probing core and shell contributions to exchange bias inCo/Co3O4nanoparticles of controlled size

Cited by 25 publications

References 59 publications

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

High-Coercivity Cobalt Nanowire Arrays: Synthesis and Heat Treatment

Giant Exchange‐Bias in Polyol‐Made CoFe₂O₄‐CoO Core–Shell Like Nanoparticles

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Probing core and shell contributions to exchange bias inCo/Co3O4nanoparticles of controlled size

Cited by 25 publications

References 59 publications

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

Maximizing Zero-Field-Cooled Exchange Bias in Crystallized Co@CoO Nanocluster Assembled Thin Film by Varying Film Thickness

High-Coercivity Cobalt Nanowire Arrays: Synthesis and Heat Treatment

Giant Exchange‐Bias in Polyol‐Made CoFe2O4‐CoO Core–Shell Like Nanoparticles

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Giant Exchange‐Bias in Polyol‐Made CoFe₂O₄‐CoO Core–Shell Like Nanoparticles