Shell-Driven Magnetic Stability in Core-Shell Nanoparticles

Nogués, J.; Skumryev, V.; Sort, Jordi; Stoyanov, S.; Givord, D.

doi:10.1103/physrevlett.97.157203

Cited by 204 publications

(196 citation statements)

References 50 publications

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“…1a, 1c and 1d). From the fits we obtain: i) an effective anisotropy constant, K eff , value about 2.510 6 50 erg/cm 3 , close to that of bulk -Co (fcc) and similar to those previously reported for fcc-Co NPs 10, 14 ; ii) an average diameter for the Co-core around 5 nm in good agreement with that of 4-6 nm estimated from TEM images and, iii) a saturation magnetization (M s ) of 156 emu/g almost equal to 55 that measured at room temperature (see inset of Fig. 5).…”

supporting

confidence: 87%

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Fernández-García

Gorría

Sevilla

et al. 2011

Phys. Chem. Chem. Phys.

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supporting

confidence: 87%

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Fernández-García

Gorría

Sevilla

et al. 2011

Phys. Chem. Chem. Phys.

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“…This translates to an enhanced energy barrier to moment reversal, resulting in thermal stability of the spins even above T B and subsequent display of EB by the sample. In the context of our analysis of exchange bias above T B based on the proposed shell-shell interaction model, we mention that similar models have earlier been proposed in literature 16,17 to elucidate the radically enhanced magnetic stability of FM cores of core-shell FM-AFM nanoparticles in contact, as compared to when the NPs were isolated. The enhanced shell thickness when the NPs come into contact was proposed to recover the bulk AFM properties of the shell, leading to better interfacial coupling, large bias fields, and an increase in the blocking temperature of the cores.…”

Section: Exchange Bias Above T B :Analysismentioning

confidence: 99%

Exchange bias beyond the superparamagnetic blocking temperature of the antiferromagnet in a Ni-NiO nanoparticulate system

Roy

Toro

Amaral

et al. 2014

Journal of Applied Physics

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We report magnetic and exchange bias studies on Ni-NiO nanoparticulate systems synthesized by a two-step process, namely, chemical reduction of a Ni salt followed by air annealing of the dried precipitate in the temperature range 400 550 C. Size of Ni and NiO crystallites as estimated from X ray diffraction line broadening ranges between 10.5 13.5 nm and 2.3 4 nm, respectively. The magneto-thermal plots (M-T) of these bi-magnetic samples show a well developed peak in the vicinity of 130 K. This has been identified as the superparamagnetic blocking temperature "T B " of NiO. Interestingly, all samples exhibit exchange bias even above their respective NiO blocking temperatures, right up to 300 K, the maximum temperature of measurement. This is in contrast to previous reports since exchange bias requires the antiferromagnetic NiO to have a stable direction of its moment in order to pin the ferromagnet (Ni) magnetization, whereas such stability is unlikely above T B since the NiO is superparamagnetic, its moment flipping under thermal activation. Our observation is elucidated by taking into account the core-shell morphology of the Ni-NiO nanoparticles whereby clustering of some of these nanoparticles connects their NiO shells to form extended continuous regions of NiO, which because of their large size remain blocked at T > T B , with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with T B denoting the blocking temperature of the NiO shell of the isolated particles. V C 2014 AIP Publishing LLC. [http://dx

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“…This can be explained as being due to the influence of the oxide shell stabilizing the core moments, as seen also in Co-CoO particles. 62 Additionally, the oxide shell is likely ferri-magnetic, which makes the effective core larger. A comparison of similar core/shell samples with similar size (Fig.…”

Section: First Order Reversal Curvesmentioning

confidence: 99%

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

McCloy

Jiang

Droubay

et al. 2013

Journal of Applied Physics

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A cluster deposition method was used to produce films of loosely aggregated nanoclusters (NC) of Fe core-Fe 3 O 4 shell or fully oxidized Fe 3 O 4 . Films of these NC on Si(100) or MgO(100)/Fe 3 O 4 (100) were irradiated to 10 16 Si 2+ /cm 2 near room temperature using an ion accelerator. Ion irradiation creates structural change in the NC film with corresponding chemical and magnetic changes which depend on the initial oxidation state of the cluster. Films were characterized using magnetometry (hysteresis, first order reversal curves), microscopy (transmission electron, helium ion), and x-ray diffraction. In all cases, the particle sizes increased due to ion irradiation, and when a core of Fe is present, irradiation reduces the oxide shells to lower valent Fe species. These results show that ion irradiated behavior of the nanocluster films depends strongly on the initial nanostructure and chemistry, but in general saturation magnetization decreases slightly.

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Shell-Driven Magnetic Stability in Core-Shell Nanoparticles

Cited by 204 publications

References 50 publications

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Exchange bias beyond the superparamagnetic blocking temperature of the antiferromagnet in a Ni-NiO nanoparticulate system

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

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