Limits...
Origin of reduced magnetization and domain formation in small magnetite nanoparticles

View Article: PubMed Central - PubMed

ABSTRACT

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12–14 nm.

No MeSH data available.


Related in: MedlinePlus

Atomically resolved HAADF STEM images of representative (a) Sun NP viewed along the [111] zone axis, (b) Colvin NP viewed along the [114] zone axis. (c) Hyeon NP along the [11-2] zone axis, obtained by rigid registration of a stack of images of the same area recorded in quick succession (resulting in high signal-to-noise and precision in the image). Dashed lines in (b) and (c) indicate the presence of the structural defects. (d) Magnified view of the dashed area shown in (c) with overlaid structural model emphasizing the defect region.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5385549&req=5

f2: Atomically resolved HAADF STEM images of representative (a) Sun NP viewed along the [111] zone axis, (b) Colvin NP viewed along the [114] zone axis. (c) Hyeon NP along the [11-2] zone axis, obtained by rigid registration of a stack of images of the same area recorded in quick succession (resulting in high signal-to-noise and precision in the image). Dashed lines in (b) and (c) indicate the presence of the structural defects. (d) Magnified view of the dashed area shown in (c) with overlaid structural model emphasizing the defect region.

Mentions: The puzzling magnetic behaviour in the ZFC curves cannot be explained by the conventional TEM and SAED observations alone, but requires deeper structural analysis. STEM imaging was used to determine the atomic structure and chemistry of selected nanoparticles, and to identify structural characteristics typical to each preparation method. The contrast dependence of high angle annular dark field (HAADF) imaging on the atomic number Z as ~Z1.7 enables direct identification of both iron tetrahedral (FeA) and octahedral (FeB) atomic columns in the NPs. Figure 2 shows atomically-resolved HAADF images of representative Sun, Colvin and Hyeon NPs. In all three cases the bulk-like magnetite structural ordering extends to the particle surfaces, and no core-shell structure is observed.


Origin of reduced magnetization and domain formation in small magnetite nanoparticles
Atomically resolved HAADF STEM images of representative (a) Sun NP viewed along the [111] zone axis, (b) Colvin NP viewed along the [114] zone axis. (c) Hyeon NP along the [11-2] zone axis, obtained by rigid registration of a stack of images of the same area recorded in quick succession (resulting in high signal-to-noise and precision in the image). Dashed lines in (b) and (c) indicate the presence of the structural defects. (d) Magnified view of the dashed area shown in (c) with overlaid structural model emphasizing the defect region.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5385549&req=5

f2: Atomically resolved HAADF STEM images of representative (a) Sun NP viewed along the [111] zone axis, (b) Colvin NP viewed along the [114] zone axis. (c) Hyeon NP along the [11-2] zone axis, obtained by rigid registration of a stack of images of the same area recorded in quick succession (resulting in high signal-to-noise and precision in the image). Dashed lines in (b) and (c) indicate the presence of the structural defects. (d) Magnified view of the dashed area shown in (c) with overlaid structural model emphasizing the defect region.
Mentions: The puzzling magnetic behaviour in the ZFC curves cannot be explained by the conventional TEM and SAED observations alone, but requires deeper structural analysis. STEM imaging was used to determine the atomic structure and chemistry of selected nanoparticles, and to identify structural characteristics typical to each preparation method. The contrast dependence of high angle annular dark field (HAADF) imaging on the atomic number Z as ~Z1.7 enables direct identification of both iron tetrahedral (FeA) and octahedral (FeB) atomic columns in the NPs. Figure 2 shows atomically-resolved HAADF images of representative Sun, Colvin and Hyeon NPs. In all three cases the bulk-like magnetite structural ordering extends to the particle surfaces, and no core-shell structure is observed.

View Article: PubMed Central - PubMed

ABSTRACT

The structural, chemical, and magnetic properties of magnetite nanoparticles are compared. Aberration corrected scanning transmission electron microscopy reveals the prevalence of antiphase boundaries in nanoparticles that have significantly reduced magnetization, relative to the bulk. Atomistic magnetic modelling of nanoparticles with and without these defects reveals the origin of the reduced moment. Strong antiferromagnetic interactions across antiphase boundaries support multiple magnetic domains even in particles as small as 12–14 nm.

No MeSH data available.


Related in: MedlinePlus