Effect of polymer coating on the magnetic properties of oxygen-stabilized nickel nanoparticles

Singh, Vidyadhar; Srinivas, V.; Ranot, Mahipal; Angappane, S.; Park, Je‐Geun

doi:10.1103/physrevb.82.054417

Cited by 32 publications

(15 citation statements)

References 36 publications

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“…[56]. A similar exponential dependence of H C (T ) was reported in Ni nanoparticles and rare-earth transition-metal magnets, where strong FM exchange and random magnetic anisotropy are present [57].…”

Section: -9supporting

confidence: 49%

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

Bohra

Grammatikopoulos

Singh

et al. 2017

Phys. Rev. Materials

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In the nanoregime, chemical species can reorganize in ways not predicted by their equilibrium bulk behavior. Here, we engineer Ni-Cr nanoalloys at the magnetic end of their compositional range (i.e., 0-15 at. % Cr), and we investigate the effect of Cr incorporation on their structural stability and resultant magnetic ordering. To ensure their stoichiometric compositions, the nanoalloys are grown by cluster beam deposition, a method that allows one-step, chemical-free fabrication of bimetallic nanoparticles. While full Cr segregation toward nanoparticle surfaces is thermodynamically expected for low Cr concentrations, metastability occurs as the Cr dopant level increases in the form of residual Cr in the core region, yielding desirable magnetic properties in a compensatory manner. Using nudged elastic band calculations, residual Cr in the core is explained based on modifications in the local environment of individual Cr atoms. The resultant competition between ferromagnetic and antiferromagnetic ordering gives rise to a wide assortment of interesting phenomena, such as a cluster-glass ground state at very low temperatures and an increase in Curie temperature values. We emphasize the importance of obtaining the commonly elusive magnetic nanophase diagram for M-Cr (M = Fe, Co, and Ni) nanoalloys, and we propose an efficient single-parameter method of tuning the Curie temperature for various technological applications.

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Section: -9supporting

confidence: 49%

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

Bohra

Grammatikopoulos

Singh

et al. 2017

Phys. Rev. Materials

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“…The total anisotropy can be given as the sum of three contributions, volume ( K V ), surface ( K S ), and shape ( K sh ) anisotropies, assuming that NiCr NPs are no longer spherical after annealing, K sh ≠ 0 where S is the surface area. 32 − 34 Normally, at low temperatures, short-range interactions due to surface spin rearrangement can eventually dominate the collective behavior of the particles. 32 In the present case, apart from bulk macroscopic properties being affected by Cr-surface segregation (e.g., enhancement in Curie temperature values), 5 low-temperature magnetic characteristics are also significantly affected in a different fashion, and a new type of surface anisotropy was developed in doped NiCr NPs.…”

Section: Resultsmentioning

confidence: 99%

Aggregation vs Surface Segregation: Antagonism over the Magnetic Behavior of NiCr Nanoparticles

et al. 2020

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Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic interactions. Herein, we study the effect of moderate annealing (450 °C) on strongly interacting NiCr nanoparticle assemblies (0 ≤ atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5−15 atom % Cr) behavior below higher spin-glass transition temperatures T g (20−350 K). The observation of "high-f ield susceptibility" below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples.

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“…Hence the overall magnetization is due to a combination of large weakly ferromagnetic Ni nanoparticles of size > 75 nm, small superparamagnetic Ni nanoparticles with size <75 nm and the paramagnetic BC. The resulting magnetization variation of the composites therefore has been fitted using the following equation [29,30],…”

Section: Discussionmentioning

confidence: 99%

Interparticle interactions mediated superspin glass to superferromagnetic transition in Ni-bacterial cellulose aerogel nanocomposites

Thiruvengadam

Vitta

2016

Journal of Applied Physics

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The interparticle interactions in a magnetic nanocomposite play a dominant role in controlling the phase transitions -superparamagnetic to superspinglass to superferromagnetic. These interactions can be tuned by controlling the size and number density of nanoparticles. Aerogel composites, 0.3 Ni-BC and 0.7 Ni-BC, consisting of Ni nanoparticles distributed in bacterial cellulose have been used as model systems to study the effect of interparticle interactions with increasing fraction of Ni in the composite. Contrary to conventional approach, the size of Ni nanoparticles is not controlled and was allowed to form naturally in the bacterial cellulose template. The structural characterization using x-ray diffraction and electron microscopies indicates the presence of only Ni and cellulose with no other phases. Thermogravimetric analysis shows that the Ni content in the two aerogels is 78 % and 83.8 % respectively. The uncontrolled growth of Ni in cellulose matrix results in the formation of nanoparticles with 3 different size distributions -< 10 nm particles mainly distributed along the length of fibrils, 50 nm particles present in the intermediate spaces between the fibrils and > 100 nm particles present in voids formed by the reticulate structure. The magnetic behavior of these composites as a function of temperature, magnetic field and frequency shows that different magnetic states can be accessed at different temperatures. At room temperature the composites exhibit a weakly ferromagnetic behavior with a coercivity of 40 Oe which increases to 160 Oe at 10 K. The magnetization at both the temperatures however is found to be non-saturating even at fields as high as 20 kOe. The transition from weakly ferromagnetic state at room temperature to a superferromagnetic state at low temperatures is mediated via a superspinglass state at intermediate temperatures.Both the superspinglass state and the superferromagnetic state are found to be sustained by the interparticle interactions aided by the presence of small nanoparticles along the length of cellulose fibres. A temperature dependent microstructural model has been developed combining the structural and magnetic results obtained from the two composite aerogels. *satish.vitta@iitb.ac.in

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Effect of polymer coating on the magnetic properties of oxygen-stabilized nickel nanoparticles

Cited by 32 publications

References 36 publications

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

Aggregation vs Surface Segregation: Antagonism over the Magnetic Behavior of NiCr Nanoparticles

Interparticle interactions mediated superspin glass to superferromagnetic transition in Ni-bacterial cellulose aerogel nanocomposites

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