Steering the magnetic properties of Ni/NiO/CoO core-shell nanoparticle films: The role of core-shell interface versus interparticle interactions

Ponti, Alessandro; Ferretti, Anna M.; Capetti, Elena; Spadaro, Maria Chiara; Bertoni, Giovanni; Grillo, Vincenzo; Luches, Paola; Valeri, Sergio; D’Addato, Sergio

doi:10.1103/physrevmaterials.1.036001

Cited by 7 publications

(5 citation statements)

References 67 publications

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“…In this model of quasi-independent hematite single-domain particles, the distribution of the coercive fields of the grains (microcoercivity spectrum) can be measured by the ΔM method. 126 As shown in Figure S18, in the NF-600 sample the grains with H C > 6 kOe are more abundant than in NF-600/25 and NF-25/600 in agreement with the dominant role of surface anisotropy in determining H C . The similarity of the coercive field (and microcoercivity spectrum) of the NF-600/25 and NF-25/600 samples seems to be fortuitously due to two compensating effects: the larger grain size of the latter, inducing a further reduction of H C that counteracts the lesser strain release.…”

Section: ■ Introductionsupporting

confidence: 68%

“…In addition to this bulk anisotropy, surface anisotropy significantly contributes to the coercive field of hematite nanoparticles up to several kOe. , The coercive field is higher for the NF-600 sample than for any of the coated NFs because of the strain release induced by the silica coating. In this model of quasi-independent hematite single-domain particles, the distribution of the coercive fields of the grains (microcoercivity spectrum) can be measured by the Δ M method . As shown in Figure S18, in the NF-600 sample the grains with H C > 6 kOe are more abundant than in NF-600/25 and NF-25/600 in agreement with the dominant role of surface anisotropy in determining H C .…”

Section: Resultsmentioning

confidence: 64%

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Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

et al. 2020

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In the last years, hematite has been utilized in a plethora of applications. High aspect-ratio nanohematite and hematite/silica core–shell nanostructures are arousing growing interest for applications exploiting their magnetic properties. Atomic layer deposition (ALD) is utilized here to produce SiO2-coated α-Fe2O3 nanofibers (NFs) through two synthetic routes, viz. electrospinning/calcination/ALD or electrospinning/ALD/calcination. The number of ALD cycles (10–100) modulates the coating thickness, while the chosen route controls the final nanostructure. Porous and partially hollow NFs are produced. Their hierarchical structure and the nature and density of the lattice defects and strain are characterized by combining electron microscopy, diffraction, and spectroscopy techniques. The uncoated hematite NFs mostly have surface-related strain, which is attributed to oxygen vacancies/Fe2+ sites. ALD coating causes microstrain release and decrease of surface states. NFs calcined after ALD have extensive bulk strain, which is ascribed to the presence of dislocations throughout the volume of the NF grains. Bulk strain determines the remanent magnetization, whereas both surface and bulk strain influence the coercive field and the thermal behavior across the Morin temperature, including the magnetic memory effect. To the best of the authors’ knowledge, the correlation between lattice defects/strain and magnetic properties of SiO2-coated α-Fe2O3 NFs has never been reported before.

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Section: ■ Introductionsupporting

confidence: 68%

Section: Resultsmentioning

confidence: 64%

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

et al. 2020

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“…Moreover, co‐deposition of different species with thermal evaporation sources is possible, in order to obtain core–shell geometry with different materials, or NPs embedded in a solid matrix . For instance, it was possible to study systematically the effect of non‐native oxide shell thickness and composition on the magnetic and structure properties of Ni@NiO, Ni@CoO, Ni@MgO, and FePt@MgO NP assemblies . In recent papers, complex core@shell and core@shell@shell NPs were obtained by modified gas aggregation sources, similar to the one used in the present work and in previous studies …”

Section: Introductionmentioning

confidence: 99%

Physical Synthesis and Study of Ag@CaF₂ Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties

D’Addato

Vikatakavi

Spadaro

et al. 2019

Physica Status Solidi (b)

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Pre‐formed Ag nanoparticles (NPs) and Ag@CaF2 core–shell NPs are physically synthesized using DC magnetron‐based NP source and deposited on Si‐SiOx wafers. The samples are prepared by co‐depositing Ag nanoparticles and CaF2 produced by an evaporation source, or by sequential deposition method, i.e., by depositing in a sequence a CaF2 buffer layer, the Ag NPs generated by the NP source and a capping CaF2 layer. The supported films are characterized by Scanning Electron Microscopy (SEM), X‐ray Photoelectron Spectroscopy (XPS), and Surface Differential Reflectivity (SDR). SEM shows that Ag NPs deposited directly on Si‐SiOx tend to diffuse and to agglomerate, affecting the size distribution of the nanostructures. The presence of a CaF2 buffer layer between Ag and Si‐SiOx limits this effect, while XPS reveals electrical charging, caused by the insulating nature of the CaF2 continuous film. The surface plasmon resonance behavior for different samples is analyzed using SDR with p‐polarized light. There is a clear evidence of a blue shift in the plasmon excitation due to the presence of CaF2 on Si, which can represent a potential advantage for the technological applications in photovoltaics and optoelectronics.

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“…A small difference (blue line) between observed (points) and calculated (red lines) values confirms an ordered La 2 NiMnO 6 phase-1 of small crystallites. A little topotactic NiO [22],2 mol%, has grown of a (220) XRD peak, d 220 =0.1485 nm; a reinforced FM-AFM composite of tunable spintronic, catalysis, and other useful properties [23][24][25]. Further, the lattice parameters a=0.5525 nm, b= 0.5484 nm, c=0.7767 nm, β=90.02°, lattice volume V c ≡ abc sinβ≅0.2353 nm 3 , and crystal density ρ=6.880 g cm −3 are obtained with an average D=80 nm crystallite size in this sample.…”

Section: Growth Of Small Core-shells In Multiple Facetsmentioning

confidence: 99%

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La₂NiMnO₆ of small crystallites

et al. 2021

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La2NiMnO6—a ferromagnetic (FM) insulator offers tunable charge carriers and spins useful to devise its multiple properties and applications. In this view, we studied a core-shell La2NiMnO6 (2–3 nm shell on 65 – 80 nm core) of a Ni2+/Ni3+(d7) to Mn4+/Mn3+ (d4) spin-up conversion— revived a new FM phase-2, raising a spin-density σ s = 0.7 s a− 1 over the Ni2+/Mn4+ species (phase-1), σ s = 0.5 s a− 1, i.e. 2.12 μB /f.u. larger spin moment. HRTEM images studied with x-ray diffraction characterizing core-shell structure that plays a crucial role in tuning the high spin FM phase-2 of profound properties. Below 110 K, the dc magnetization and ac magnetic susceptibility χ(ω, T) reveal a metastable magnetic behavior on an antiferromagnetic canting of a spin-glass nature. The results follow a Vogel–Fulcher type relaxation with a relaxation time τ 0 ∼ 10−13 s, confirming a spin-glass freezing behavior. Uniquely, FM field of phase-1 controls magnetics of phase 2 of a coupled magnet, modulating joint features with small thermal magnetic hysteresis on heating-cooling cycles.

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Steering the magnetic properties of Ni/NiO/CoO core-shell nanoparticle films: The role of core-shell interface versus interparticle interactions

Cited by 7 publications

References 67 publications

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

Physical Synthesis and Study of Ag@CaF₂ Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La₂NiMnO₆ of small crystallites

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Steering the magnetic properties of Ni/NiO/CoO core-shell nanoparticle films: The role of core-shell interface versus interparticle interactions

Cited by 7 publications

References 67 publications

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

Physical Synthesis and Study of Ag@CaF2 Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La2NiMnO6 of small crystallites

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Product

Resources

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Physical Synthesis and Study of Ag@CaF₂ Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La₂NiMnO₆ of small crystallites