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Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape.

Kumar H, Ghosh S, Avasthi DK, Kabiraj D, Mücklich A, Zhou S, Schmidt H, Stoquert JP - Nanoscale Res Lett (2011)

Bottom Line: The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing.Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles.Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India. hsehgal_007@yahoo.com.

ABSTRACT
Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

No MeSH data available.


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M-H curve measured at 5 K. For (a) pristine and (b) irradiated film with a maximum magnetic field of 20 kOe applied parallel and perpendicular to ion beam direction
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Figure 3: M-H curve measured at 5 K. For (a) pristine and (b) irradiated film with a maximum magnetic field of 20 kOe applied parallel and perpendicular to ion beam direction

Mentions: In order to observe the effect of irradiation on magnetic properties, magnetization curves were measured at 5 K in a magnetic field applied both parallel (out-plane measurement) and perpendicular (in-plane measurement) to the ion beam direction. The M-H curves for pristine and irradiated film are shown in Figure 3a,b, respectively. The extracted coercivity (Hc) and remanence ratio (Mr/Ms) from Figure 3a,b are given in Table 1. It is clear from Figure 3a that the pristine film has a small magnetic anisotropy with easy axis in the direction perpendicular to ion beam (in-plane). The origin of in-plane easy axis is the over-all thin film-like structure, i.e., anisotropy arising from the shape effect results in an in-plane easy axis, as similarly observed in case of Fe: SiO2 granular films [25,26]. The other factors like magneto-crystalline, magnetostriction and shape anisotropy may be neglected as pristine film is polycrystalline in nature and without stress as confirmed by X-ray diffraction studies (figure not shown) containing spherical Ni particles (see Figure 1a). However, after 120 MeV Au+9 ion irradiation, the change in Hc and Mr/Ms values is much larger in the direction parallel to Au ion beam than in the perpendicular direction, which can be correlated with the elongation/formation of prolate shape Ni particles in the beam direction. Hence, magnetic shape anisotropy appears in the elongated Ni NPs with easy axis in the direction of elongation. However, a macroscopic magnetic anisotropy with easy axis in the ion beam direction is not observed due to the existence of some spherical Ni particles in addition to deformed prolate particles in the irradiated film.


Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape.

Kumar H, Ghosh S, Avasthi DK, Kabiraj D, Mücklich A, Zhou S, Schmidt H, Stoquert JP - Nanoscale Res Lett (2011)

M-H curve measured at 5 K. For (a) pristine and (b) irradiated film with a maximum magnetic field of 20 kOe applied parallel and perpendicular to ion beam direction
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211206&req=5

Figure 3: M-H curve measured at 5 K. For (a) pristine and (b) irradiated film with a maximum magnetic field of 20 kOe applied parallel and perpendicular to ion beam direction
Mentions: In order to observe the effect of irradiation on magnetic properties, magnetization curves were measured at 5 K in a magnetic field applied both parallel (out-plane measurement) and perpendicular (in-plane measurement) to the ion beam direction. The M-H curves for pristine and irradiated film are shown in Figure 3a,b, respectively. The extracted coercivity (Hc) and remanence ratio (Mr/Ms) from Figure 3a,b are given in Table 1. It is clear from Figure 3a that the pristine film has a small magnetic anisotropy with easy axis in the direction perpendicular to ion beam (in-plane). The origin of in-plane easy axis is the over-all thin film-like structure, i.e., anisotropy arising from the shape effect results in an in-plane easy axis, as similarly observed in case of Fe: SiO2 granular films [25,26]. The other factors like magneto-crystalline, magnetostriction and shape anisotropy may be neglected as pristine film is polycrystalline in nature and without stress as confirmed by X-ray diffraction studies (figure not shown) containing spherical Ni particles (see Figure 1a). However, after 120 MeV Au+9 ion irradiation, the change in Hc and Mr/Ms values is much larger in the direction parallel to Au ion beam than in the perpendicular direction, which can be correlated with the elongation/formation of prolate shape Ni particles in the beam direction. Hence, magnetic shape anisotropy appears in the elongated Ni NPs with easy axis in the direction of elongation. However, a macroscopic magnetic anisotropy with easy axis in the ion beam direction is not observed due to the existence of some spherical Ni particles in addition to deformed prolate particles in the irradiated film.

Bottom Line: The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing.Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles.Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India. hsehgal_007@yahoo.com.

ABSTRACT
Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 × 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.

No MeSH data available.


Related in: MedlinePlus