Novel highly ordered core–shell nanoparticles

Dey, Sonal; Hossain, Mohammad Delower; Mayanovic, Robert A.; Wirth, Richard; Gordon, R. A.

doi:10.1007/s10853-016-0495-2

Cited by 13 publications

(9 citation statements)

References 37 publications

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“…Conversely, the lowest EB field value was measured from sample B1, which has only the Mn x Ni 1– x O epitaxial shell overgrowth in the MHNCs. This is consistent with the magnetometry results from our previous studies, in which we used the hydrothermal nanophase epitaxy technique to synthesize a series of Cr 2 O 3 /M x Cr 2–x O 3 (M: Fe, Ni, Co, Mn) epitaxial core–shell nanoparticles. ,, On the basis of the substitutional cation M, EB fields (20–400 Oe) at 5K were observed for the Cr 2 O 3 /M x Cr 2–x O 3 core–shell nanoparticles, which is in the range of the EB field value recorded for sample B1 of the present study. ,,, The present study suggests that epitaxial shell formation through 3d transition metal element substitution may induce a small EB effect and a lower coercivity, but heterostructure phase selectivity through regulation of hydrothermal solution pH value presents an opportunity to amplify the magnetic response and may help tailor heterostructured nanoparticles for real-world applications.…”

Section: Computational Analysissupporting

confidence: 89%

“…Next, our hydrothermal nanophase epitaxy process was used to grow the Mn-bearing oxide phases over the NiO core. ,− First, MnCl 2 ·3H 2 O was added to DI water after the water was purged of O 2 using N 2 for 15–20 min at a temperature of 70–80 °C. Eight samples were prepared from aqueous solutions, with pH values ranging from 2.4–7.0 and adjusted by adding drops of HCl or NaOH.…”

Section: Experimental and Computational Detailsmentioning

confidence: 99%

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Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals

Shafe

Hossain

Mayanovic

et al. 2021

ACS Appl. Mater. Interfaces

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A series of bimagnetic heterostructured nanocrystals having an antiferromagnetic NiO core and a ferrimagnetic Mn x Ni1–x O and/or FiM Mn3O4 island nanophase overgrowth has been synthesized under varying aqueous solution pH conditions. The two-step self-assembly process employs a thermal decomposition method to synthesize NiO nanoparticles, followed by growth of the Mn x Ni1–x O and/or Mn3O4 nanophase over the NiO core using hydrothermal synthesis at pH values ranging from 2.4–7.0. The environmentally benign hydrothermal process involves pH control of the protonation vs hydroxylation reactions occurring at the nanoparticle surface. TEM analysis and Rietveld refinement of XRD data show that three distinct types of heterostructured nanocrystals occur: NiO/Mn x Ni1–x O core–shell-like heterostructures at the pH of 2.4, mixed NiO/Mn x Ni1–x O and/or/Mn3O4 core-overgrowth structures for 2.4 < pH < 4.5, and predominantly NiO/Mn3O4 core-island structures for pH > 4.5. The magnetic coercivity and exchange bias of the heterostructured nanocrystals vary systematically with the pH of the aqueous solution used to synthesize the samples. The temperature-dependent magnetization and hysteresis loop data are consistent with the nature of overlayer coverage of the NiO core. Our DFT based calculations show that the Mn x Ni1–x O phase has ferrimagnetic properties with a stable spin orientation along the ⟨111⟩ orientation. Furthermore, the calculations show that the magnetic anisotropy constant (K 1) of the Mn3O4 phase is considerably larger than that of the Mn x Ni1–x O phase, which is confirmed by our experimental results. The coercivity and exchange bias field are the largest for the NiO/Mn3O4 core-island nanocrystals, synthesized at a pH value of 5.0, with robust values of nearly 6 kOe and 3 kOe, respectively. This work demonstrates the tunability of hydrothermal deposition, and concomitant magnetic coercivity and exchange bias properties, of Mn x Ni1–x O and/or Mn3O4 nanophase overgrowth over a NiO core with pH, that makes these heterostructured nanocrystals potentially useful for magnetic device, biomedical, and other applications.

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Section: Computational Analysissupporting

confidence: 89%

Section: Experimental and Computational Detailsmentioning

confidence: 99%

Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals

Shafe

Hossain

Mayanovic

et al. 2021

ACS Appl. Mater. Interfaces

Self Cite

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“…We have developed a nature-inspired hydrothermal nanophase epitaxy (HNE) method for synthesis of highly ordered AFM core and a FM/FiM shell Cr 2 O 3 -based CSNs. [28][29][30] By imitating mineral zonation that occurs naturally under hydrothermal conditions, 31 we are able to grow an epitaxial highly structurally ordered a-M x Cr 2Àx O 3Ày shell (M: Co, Fe, Ni, Mn) covering a a-Cr 2 O 3 nanocrystalline core to form a-Cr 2 O 3 @a-M x Cr 2Àx O 3Ày inverted CSNs. Our methodology employs a two-step process.…”

Section: Experimental Methodsmentioning

confidence: 99%

Room-temperature ferromagnetism in Ni(ii)-chromia based core–shell nanoparticles: experiment and first principles calculations

Hossain

Mayanovic

Dey

et al. 2018

Phys. Chem. Chem. Phys.

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We have synthesized bimagnetic core-shell nanoparticles containing a first-of-its-kind Ni(ii)-chromia nanophase shell and a well-defined, epitaxial core-shell interface. Magnetic measurements reveal a substantial coercivity of the nanoparticles and a significant exchange bias effect between the antiferromagnetic chromia core and the ferromagnetic Ni(ii)-chromia shell at low temperatures. The ferromagnetism and a weak exchange bias effect are found to persist to room temperature in the core-shell nanoparticles of ∼57 nm average size. Our first principles Density Functional Theory (DFT) calculations confirm that the novel corundum-structured Ni(ii)-chromia phase has an equilibrium cluster-localized ferromagnetic spin configuration. In addition, the DFT-based calculations show that the Ni(ii)-chromia phase is a Mott-Hubbard insulator, with a narrowed energy band gap and increased covalent bonding due to strong hybridization between Ni 3d and O 2p levels in the upper portion of the valence band and within the band gap region. The antiferromagnetic, ferromagnetic and magnetoelectric properties of our core-shell nanoparticles make these well suited for patterned recording media and biomedical applications.

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“…It is still unclear as to how the exchange bias effect is dependent upon the geometry of Co 3 O 4 -based bimagnetic nanostructures. Herein we used our hydrothermal nanophase epitaxy (HNE) method [12,13] to prepare Co 3 O 4 @Mn x Co 3-x O 4 inverted CSNs with two different morphologies for the first time, and addressed the question as to how the magnetic properties depend upon their shape. Our bimagnetic CSNs were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a SQUID magnetometry.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Characterization of Co3O4-MnxCo3-xO4 Core-Shell Nanoparticles

2018

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The mixed-valence oxide Co3O4 nanoparticles, having the normal spinel structure, possess large surface area, active-site surface adsorption properties, and fast ion diffusivities. Consequently, they are widely used in lithium-ion batteries, as well as for gas sensing and heterogeneous catalysis applications. In our research, we use a two-step method to synthesize Co3O4–based core-shell nanoparticles (CSNs). Cobalt oxide (Co3O4) nanoparticles were successfully synthesized using a wet synthesis method employing KOH and cobalt acetate. Manganese was incorporated into the Co3O4 structure to synthesize inverted Co3O4@MnxCo3-xO4 CSNs using a hydrothermal method. By adjustment of pH value, we obtained two different morphologies of CSNs, one resulting in pseudo-spherical and octahedron-shaped nanoparticles (PS type) whereas the second type predominantly have a nanoplate (NP type) morphology. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) have been performed in order to determine the morphological and structural properties of our CSNs, whereas the magnetic properties have been characterized using a superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the CSNs have the same spinel crystal structure throughout the core and shell with an average particle size of ∼19.8 nm. Our Co3O4 nanoparticles, as measured prior to CSN formation, are shown to be antiferromagnetic (AFM) in nature as shown by the magnetization data. Our SQUID data indicate that the core-shell nanoparticles have both AFM (due to the Co3O4 core) and ferrimagnetic properties (of the shell) with a coercivity field of 300 Oe and 150 Oe at 5 K for the PS and NP samples, respectively. The magnetization vs temperature data show a spin order-disorder transition at ∼33 K and a superparamagnetic blocking temperature of ∼90 K for both batches.

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Novel highly ordered core–shell nanoparticles

Cited by 13 publications

References 37 publications

Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals

Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals

Room-temperature ferromagnetism in Ni(ii)-chromia based core–shell nanoparticles: experiment and first principles calculations

Synthesis and Characterization of Co3O4-MnxCo3-xO4 Core-Shell Nanoparticles

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