Exchange anisotropy in oxide passivated Co fine particles

Gangopadhyay, S.; Hadjipanayis, G. C.; Sorensen, C. M.; Klabunde, K. J.

doi:10.1063/1.352398

Cited by 134 publications

(89 citation statements)

References 12 publications

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“…Among the most important theoretical results [9] we mention (i) the disappearance of the exchange bias field * corresponding author; e-mail: trohidou@ims.demokritos.gr (H E ) at temperatures above the Néel temperature of the AFM, in agreement with experiments [10], (ii) the strong dependence of the exchange field H E of the number uncompensated bonds across the FM-AFM interface and the dependence of the coercive field H C on the interface area, (iii) the increase in both H E and H C for a given nanoparticle radius with increasing shell thickness, (iv) the increase in H E and decrease in H C with increasing oxidation layer thickness and a fixed core radius, (v) the fast stabilization of H E with increasing core size, in agreement with experiments [11], and (vi) the reduction in H C and increase in H E and its thermal stability with increasing exchange constant of the AFM material and/or at the FM-AFM interface. Despite the research effort focused on the microscopic mechanism of the exchange bias effect in individual nanoparticles [9,12], much less attention has been paid so far to the modification of the magnetic hysteresis behaviour due to inter-particle interactions arising in assemblies.…”

Section: Introductionsupporting

confidence: 73%

Magnetic Behaviour of Core/Shell Nanoparticle Assemblies: Interparticle Interactions Effects

Trohidou

Vasilakaki

2010

Acta Phys. Pol. A

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Interparticle interactions in assemblies of nanoparticles represent an important effect that modifies their magnetic behavior. The characteristics of the hysteresis loop and the temperature dependent magnetization (field cooled (FC)/zero-field cooled (ZFC)) are studied numerically in magnetic nanoparticle assemblies using Monte Carlo simulations and the standard Metropolis algorithm. We study composite spin nanostructures with ferromagnetic (FM) core/antiferromagnetic (AFM) shell morphology and simple ferromagnetic nanostructures. Both three-dimensional granular solids and two-dimensional ordered nanoparticle arrays are analyzed and compared, with emphasis on the interplay between single-particle characteristics and magnetostatic interparticle interactions. We find that the antiferromagnetic interface provides a strong exchange coupling with the ferromagnetic core and, through it, an effective long range interparticle correlation, modified from that of simple FM nanostructures. The results of our simulations are compared with experimental findings.

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Section: Introductionsupporting

confidence: 73%

Magnetic Behaviour of Core/Shell Nanoparticle Assemblies: Interparticle Interactions Effects

Trohidou

Vasilakaki

2010

Acta Phys. Pol. A

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“…The EB field and vertical shift are defined as A first notable feature is the nonmonotonic behavior of H E and H C presented in Figs. 5(a) and 5(b), which has been reported previously for Co/CoO nanoparticles [8,40,46,47]. An argument based on an energetic balance between exchange coupling and anisotropy in coupled FM/AF thin films with ideal interfaces indicate that EB should grow following a 1/d F M law [6] when the thickness of the FM is reduced, resulting from the increase in surface to volume ratio of the FM.…”

Section: Magnetic Characterizationmentioning

confidence: 75%

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

De¹,

Iglesias

Majumdar

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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“…The existence of EB in such systems is thus limited to temperatures below the SPM blocking temperature of the AFM component. 5,6 Thus, an attempt to combat the SPM limit in nanoparticulate magnetic recording media utilizing the EB effect seems to be thwarted by an additional problem overcoming superparamagnetic fluctuations in the AFM component, more specifically those with small magnetic anisotropy.…”

mentioning

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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Exchange anisotropy in oxide passivated Co fine particles

Cited by 134 publications

References 12 publications

Magnetic Behaviour of Core/Shell Nanoparticle Assemblies: Interparticle Interactions Effects

Magnetic Behaviour of Core/Shell Nanoparticle Assemblies: Interparticle Interactions Effects

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

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

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