The size-dependent magnetic properties of Co3O4 nanoparticles

Ichiyanagi, Yuko; Yamada, Shigenori

doi:10.1016/j.poly.2005.03.158

“…To the best of our knowledge, this is one of the smallest sizes reported for free Co 3 O 4 nanocrystallites in the literature. 57 In contrast, TEM micrographs of Co 3 O 4 nano- , followed by (2) slow, autocatalytic release of NH 3 from this complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca.…”

Section: −52mentioning

confidence: 97%

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

Alvarado

¹

,

Guo

²

,

Ruberu

³

et al. 2012

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Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (~3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH 3 ) 5 Cl]Cl 2 , under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in the presence of light, does not involve a free radical mechanism, is insensitive to O 2, and proceeds in two steps: (1) Aquation of [Co(NH 3 ) 5 Cl] 2+ to yield [Co(NH 3 ) 5 (H 2 O)] 3+ , followed by (2) slow photoinduced release of NH 3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (~250 nm) polydisperse Co(O)OH aggregates. UV-Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co 3 O 4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to T = 64 degrees C) for small nanocrystals compared with the bulk. KeywordsAb initio calculations, Aqua complexes, Catalytic properties, control experiments, fast thermal annealing, free radical mechanism, high-temperature pyrolysis, low temperatures, monodisperse, nanoparticle sizes, neutral pH, Oxyhydroxides, Pentaamminechlorocobalt, Photochemical method, thermal synthesis, chlorine compounds, cobalt, cracking (chemical) Disciplines Chemistry CommentsReprinted (adapted) with permission from Journal of Physical Chemistry C 116 (2012)

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“…In the case of Co NP, most of the published studies [23] report the formation of the CoO phase on the shell, although in some cases the presence of the Co 3 O 4 has also been evidenced by structural [24,25] or magnetic characterization [26], The possibility of observing EB in Co based nanostructures in contact with Co 3 O 4 has been rather less investigated and the published studies focus on layered structures [27][28][29][30][31]. Synthesis of single phase CoO or Co 3 O 4 NP have been achieved by several authors, that have reported AF magnetic behavior with ordering temperatures reduced compared to the bulk values [32][33][34] and remanence values much higher than those for the bulk due to finite-size effects [26,35].…”

Section: Introductionmentioning

confidence: 99%

Probing core and shell contributions to exchange bias in Co/Co<inf>3</inf>O<inf>4</inf> nanoparticles of controlled size

De¹,

Iglesias

²

,

Majumdar

³

et al. 2017

2017 IEEE International Magnetics Conference (INTERMAG)

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Coupling at the interface of core/shell magnetic nanoparticles is known to be responsible for exchange bias (EB) and the relative sizes of core and shell components are supposed to influence the associated phenomenology. In this work, we have prepared core/shell structured nanoparticles with a total average diameter around ∼27 nm and a wide range of shell thicknesses through the controlled oxidation of Co nanoparticles well dispersed in an amorphous silica host. Structural characterizations give compelling evidence of the formation of Co 3 O 4 crystallite phase at the shells surrounding the Co core. Field cooled hysteresis loops display nonmonotonous dependence of the exchange bias H E and coercive H C fields, that become maximum for a sample with an intermediate shell thickness, at which lattice strain is also maximum for both phases. The EB effects persist up to temperatures above the ordering temperature of the oxide shell. Results of our atomistic Monte Carlo simulations of particles with the same size and composition as in experiments are in agreement with the experimental observations and have allowed us to identify a change in the contribution of the interfacial surface spins to the magnetization reversal, giving rise to the observed maximum in H E and H C .

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“…In the case of Co NP, most of the published studies [23] report the formation of the CoO phase on the shell, although in some cases the presence of the Co 3 O 4 has also been evidenced by structural [24,25] or magnetic characterization [26], The possibility of observing EB in Co based nanostructures in contact with Co 3 O 4 has been rather less investigated and the published studies focus on layered structures [27][28][29][30][31]. Synthesis of single phase CoO or Co 3 O 4 NP have been achieved by several authors, that have reported AF magnetic behavior with ordering temperatures reduced compared to the bulk values [32][33][34] and remanence values much higher than those for the bulk due to finite-size effects [26,35].…”

Section: Introductionmentioning

confidence: 99%

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

De

¹

,

Iglesias

²

,

Majumdar

³

et al. 2016

View full text Add to dashboard Cite

Coupling at the interface of core/shell magnetic nanoparticles is known to be responsible for exchange bias (EB) and the relative sizes of core and shell components are supposed to influence the associated phenomenology. In this work, we have prepared core/shell structured nanoparticles with a total average diameter around ∼27 nm and a wide range of shell thicknesses through the controlled oxidation of Co nanoparticles well dispersed in an amorphous silica host. Structural characterizations give compelling evidence of the formation of Co 3 O 4 crystallite phase at the shells surrounding the Co core. Field cooled hysteresis loops display nonmonotonous dependence of the exchange bias H E and coercive H C fields, that become maximum for a sample with an intermediate shell thickness, at which lattice strain is also maximum for both phases. The EB effects persist up to temperatures above the ordering temperature of the oxide shell. Results of our atomistic Monte Carlo simulations of particles with the same size and composition as in experiments are in agreement with the experimental observations and have allowed us to identify a change in the contribution of the interfacial surface spins to the magnetization reversal, giving rise to the observed maximum in H E and H C .

show abstract

The size-dependent magnetic properties of Co3O4 nanoparticles

Cited by 94 publications

References 7 publications

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

Probing core and shell contributions to exchange bias in Co/Co<inf>3</inf>O<inf>4</inf> nanoparticles of controlled size

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

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