Critical radius for exchange bias in naturally oxidized Fe nanoparticles

Martínez-Boubeta, C.; Simeonidis, K.; Angelakeris, M.; Pazos-Pérez, Nicolás; Giersig, Michael; Delimitis, A.; Nalbandian, L.; Alexandrakis, V.; Niarchos, D.

doi:10.1103/physrevb.74.054430

Cited by 109 publications

(80 citation statements)

References 38 publications

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“…The different contrast obtained by TEM between the darker core and the lighter shell of the nanoparticles after room temperature oxidation suggests their uncomplete oxidation. X-ray diffraction of these samples 20 Similar examples, showing that the phase of the 3d-metal oxides depends on the size of the nanoparticles, have also been recently reported for Fe 21 and Mn, 22 most probably indicating that cation vacancies are formed as a result of the metal oxide passivation.…”

Section: Resultssupporting

confidence: 72%

“…21 Therefore, the enhancement of exchange bias, for about 30% comparing samples 3 and 4, is attributed to the thickening of the shell since the cobalt core diameter remains the same (5 nm). For instance, the anisotropy energy of a CoO shell is proportional to the term (R 3 − r 3 ), where R and r are the particle and the core radius, respectively.…”

Section: Magnetic Characterizationmentioning

confidence: 92%

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Morphology influence on nanoscale magnetism of Co nanoparticles: Experimental and theoretical aspects of exchange bias

et al. 2011

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Co-based nanostructures ranging from core/shell to hollow nanoparticles were prepared by varying the reaction time and the chemical environment during the thermal decomposition of Co 2 (CO) 8 . Both structural characterization and kinetic model simulation illustrate that the diffusivities of cobalt and oxygen determine the growth ratio and the final morphology of the nanoparticles. Exchange coupling between Co and Co-oxide in core/shell nanoparticles induced a shift of field-cooled hysteresis loops that is proportional to the shell thickness, as verified by numerical studies. The increasing nanocomplexity, when passing from core/shell to hollow particles, also leads to the appearance of hysteresis above 300 K due to an enhancement of the surface anisotropy resulting from the additional spin-disordered surfaces.

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Section: Resultssupporting

confidence: 72%

Section: Magnetic Characterizationmentioning

confidence: 92%

Morphology influence on nanoscale magnetism of Co nanoparticles: Experimental and theoretical aspects of exchange bias

et al. 2011

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“…1, we observe that M s at 5 K is about a factor 8 smaller for the FePt NPs and at RT the magnetization at 50 kOe is about 1 emu/ g. Similar very low values of M s have been also reported for "as prepared" FePt NPs. [3][4][5] In the case of iron oxide NPs, it is usually reported that the values of M s are smaller than the bulk values 17,18 and the behavior follows that the smaller the size is, the smaller the M s . Magnetite NPs synthesized by high temperature decomposition of organic precursors with diameters ranging from 5.7 to 11 nm have M s values at 5 K close to those reported for bulk Fe 3 O 4 ; at RT, M s slightly decreases as the particle diameter decreases.…”

Section: Discussionmentioning

confidence: 98%

Spontaneous oxidation of disordered fcc FePt nanoparticles

Presa

Rueda

Hernando

et al. 2008

Journal of Applied Physics

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In this work we present new results on spontaneous oxidation of disordered fcc FePt nanoparticles. The "as-made" oleic acid and oleylamine coated FePt nanoparticles of average size 4 nm synthesized by a high-boiling coordinating solvent method were exposed to air over a period of days and characterized structurally and magnetically by means of different techniques such as XANES, XPS, EXAFS, and SQUID magnetometry. The "as-made" FePt nanoparticles stabilize in the disordered fcc structure and have a very low magnetic saturation ͑M s = 11 emu/ g͒ and a huge coercive field ͑H c = 1800 Oe͒ compared to the low temperature bulk values of the disordered fcc FePt. We observed that the coercive field and the magnetic saturation change with the time the sample is exposed to air and these changes are associated with the oxidation or passivation of the nanoparticle surface that gives place to a core-shell structure. Indeed, the study on the electronic properties of the nanoparticles confirms the magnetic results and indicates that when the nanoparticles are exposed to air, changes in the oxidation state of both Fe and Pt occur, the oxidation state of Fe coming close to hematite. The formation of hematite tends to soften the "as-made" FePt nanoparticles as observed by the reduction of the coercive field to almost one third of the original value. Although the hematite softens the FePt nanoparticles, there is an exchange coupling at the interface of the core-shell characterized by the increase of the coercive field from 300 to 900 Oe when the sample is cooled in an applied field of 50 kOe.

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“…This observation supported the idea of stabilization of the iron precursor by forming a strong iron oleate complex. Depending on the solvent, oxidative agents, and temperature used, thermal decomposition of Fe(CO) 5 [39,40] which have only a slight difference between their crystal lattices (ca. 1% difference in the cubic lattice constant of the same spinel crystal structure).…”

mentioning

confidence: 99%

“…[40] It was shown that surface spin disorder can lead to the appearance of exchange anisotropy, and the existence of a spin-glass-like phase around the magnetic particles was proposed. [49,51] The origin of this surface spin-glass layer is associated with broken bonds and the translational symmetry distortion.…”

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confidence: 99%

Gold/Iron Oxide Core/Hollow‐Shell Nanoparticles

Shevchenko

Bodnarchuk²,

Kovalenko³

et al. 2008

Advanced Materials

310

277

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Gold/iron oxide core/hollow‐shell composite nanoparticles (NPs) with controllable shell thicknesses are synthesized (see figure). The gap between the Au core and iron oxide shell is formed as a result of different outward and inward diffusion rates of Fe and O, respectively. Control over interparticle interactions allows encapsulation of several Au cores inside one iron oxide shell. Superparamagnetic measurements of the NPs at room temperature demonstrate the plasmon resonance at 565 nm.

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Critical radius for exchange bias in naturally oxidized Fe nanoparticles

Cited by 109 publications

References 38 publications

Morphology influence on nanoscale magnetism of Co nanoparticles: Experimental and theoretical aspects of exchange bias

Morphology influence on nanoscale magnetism of Co nanoparticles: Experimental and theoretical aspects of exchange bias

Spontaneous oxidation of disordered fcc FePt nanoparticles

Gold/Iron Oxide Core/Hollow‐Shell Nanoparticles

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