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Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles.

Almeida TP, Kasama T, Muxworthy AR, Williams W, Nagy L, Hansen TW, Brown PD, Dunin-Borkowski RE - Nat Commun (2014)

Bottom Line: Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism.However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance.Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.

ABSTRACT
Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.

No MeSH data available.


Visualized effect of oxidation on the magnetization of an elongated Fe3O4 particle.Bright-field TEM images acquired (a) before and (b) after in situ heating to 700 °C under 9 mbar of O2 for 8 h in an ETEM, with associated SAED patterns (inset) indexed to Fe3O4 (JCPDS No. 75–449). (c) Associated EEL spectra of the Fe 2p L2,3 edge acquired from the Fe3O4 particle before (blue) and after (red) annealing within the ETEM. Red arrows highlight the formation of pre- and post-peaks that indicate oxidation towards γ-Fe2O3. (d,e) Magnetic induction maps determined from the magnetic contribution to the phase shift reconstructed from holograms taken (d) before and (e) after in situ heating, revealing the PSD nature of the particle. The contour spacing is 0.20 radians for both magnetic induction maps. The magnetization direction is shown using arrows, as depicted in the colour wheel. Scale bars represent 100 nm.
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f3: Visualized effect of oxidation on the magnetization of an elongated Fe3O4 particle.Bright-field TEM images acquired (a) before and (b) after in situ heating to 700 °C under 9 mbar of O2 for 8 h in an ETEM, with associated SAED patterns (inset) indexed to Fe3O4 (JCPDS No. 75–449). (c) Associated EEL spectra of the Fe 2p L2,3 edge acquired from the Fe3O4 particle before (blue) and after (red) annealing within the ETEM. Red arrows highlight the formation of pre- and post-peaks that indicate oxidation towards γ-Fe2O3. (d,e) Magnetic induction maps determined from the magnetic contribution to the phase shift reconstructed from holograms taken (d) before and (e) after in situ heating, revealing the PSD nature of the particle. The contour spacing is 0.20 radians for both magnetic induction maps. The magnetization direction is shown using arrows, as depicted in the colour wheel. Scale bars represent 100 nm.

Mentions: Figure 3 illustrates the effect of accelerated oxidation on the magnetization of an elongated (~250 nm long, ~150 nm wide) Fe3O4 grain. The bright-field TEM image of Fig. 3a shows the grain morphology, while the associated SAED pattern (Fig. 3a, inset) indexes to Fe3O4, again supported by the complementary characteristic EEL spectrum of Fig. 3c. The corresponding magnetic induction map of Fig. 3d reveals closely spaced magnetic contours flowing from left to right through the elongated particle, interacting with a small vortex located at the bottom, along with a component of stray magnetic field, which is indicative of a PSD state.


Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles.

Almeida TP, Kasama T, Muxworthy AR, Williams W, Nagy L, Hansen TW, Brown PD, Dunin-Borkowski RE - Nat Commun (2014)

Visualized effect of oxidation on the magnetization of an elongated Fe3O4 particle.Bright-field TEM images acquired (a) before and (b) after in situ heating to 700 °C under 9 mbar of O2 for 8 h in an ETEM, with associated SAED patterns (inset) indexed to Fe3O4 (JCPDS No. 75–449). (c) Associated EEL spectra of the Fe 2p L2,3 edge acquired from the Fe3O4 particle before (blue) and after (red) annealing within the ETEM. Red arrows highlight the formation of pre- and post-peaks that indicate oxidation towards γ-Fe2O3. (d,e) Magnetic induction maps determined from the magnetic contribution to the phase shift reconstructed from holograms taken (d) before and (e) after in situ heating, revealing the PSD nature of the particle. The contour spacing is 0.20 radians for both magnetic induction maps. The magnetization direction is shown using arrows, as depicted in the colour wheel. Scale bars represent 100 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214405&req=5

f3: Visualized effect of oxidation on the magnetization of an elongated Fe3O4 particle.Bright-field TEM images acquired (a) before and (b) after in situ heating to 700 °C under 9 mbar of O2 for 8 h in an ETEM, with associated SAED patterns (inset) indexed to Fe3O4 (JCPDS No. 75–449). (c) Associated EEL spectra of the Fe 2p L2,3 edge acquired from the Fe3O4 particle before (blue) and after (red) annealing within the ETEM. Red arrows highlight the formation of pre- and post-peaks that indicate oxidation towards γ-Fe2O3. (d,e) Magnetic induction maps determined from the magnetic contribution to the phase shift reconstructed from holograms taken (d) before and (e) after in situ heating, revealing the PSD nature of the particle. The contour spacing is 0.20 radians for both magnetic induction maps. The magnetization direction is shown using arrows, as depicted in the colour wheel. Scale bars represent 100 nm.
Mentions: Figure 3 illustrates the effect of accelerated oxidation on the magnetization of an elongated (~250 nm long, ~150 nm wide) Fe3O4 grain. The bright-field TEM image of Fig. 3a shows the grain morphology, while the associated SAED pattern (Fig. 3a, inset) indexes to Fe3O4, again supported by the complementary characteristic EEL spectrum of Fig. 3c. The corresponding magnetic induction map of Fig. 3d reveals closely spaced magnetic contours flowing from left to right through the elongated particle, interacting with a small vortex located at the bottom, along with a component of stray magnetic field, which is indicative of a PSD state.

Bottom Line: Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism.However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance.Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.

ABSTRACT
Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.

No MeSH data available.