Limits...
Magnetic Nanoparticle Arrays Self-Assembled on Perpendicular Magnetic Recording Media.

Mohtasebzadeh AR, Ye L, Crawford TM - Int J Mol Sci (2015)

Bottom Line: This increase suggests magnetic nanoparticle interactions evolve from nanoparticle-nanoparticle interactions to cluster-cluster interactions as opposed to feature-feature interactions.We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media.If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials.

View Article: PubMed Central - PubMed

Affiliation: Smart State Center for Experimental Nanoscale Physics, Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA. ramoh87@gmail.com.

ABSTRACT
We study magnetic-field directed self-assembly of magnetic nanoparticles onto templates recorded on perpendicular magnetic recording media, and quantify feature width and height as a function of assembly time. Feature widths are determined from Scanning Electron Microscope (SEM) images, while heights are obtained with Atomic Force Microscopy (AFM). For short assembly times, widths were ~150 nm, while heights were ~14 nm, a single nanoparticle on average with a 10:1 aspect ratio. For long assembly times, widths approach 550 nm, while the average height grows to 3 nanoparticles, ~35 nm; a 16:1 aspect ratio. We perform magnetometry on these self-assembled structures and observe the slope of the magnetic moment vs. field curve increases with time. This increase suggests magnetic nanoparticle interactions evolve from nanoparticle-nanoparticle interactions to cluster-cluster interactions as opposed to feature-feature interactions. We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media. If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials.

No MeSH data available.


Magnetic moment as a function of external magnetic field for assembled nanoparticle patterns for different coating times measured: (A) with lines parallel to the applied field; and (B) with lines perpendicular to the magnetic field. Note the increase in slope as time increases. Since the slope change occurs for both orientations of magnetic field, it is likely not due to the increasing pattern width but due to clustering effects within the patterns, i.e., not pattern–pattern interaction; Panel (C) shows the average slope of the m-H curve obtained at 20 and 100 Oe as a function of coating time, and while at long times, the perpendicular field loops have a lower slope than the parallel loops, the error bars overlap and thus beyond the slope change due to increasing feature size that is isotropic with direction, no difference between parallel and perpendicular fields can be claimed from the data.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4581324&req=5

ijms-16-19769-f006: Magnetic moment as a function of external magnetic field for assembled nanoparticle patterns for different coating times measured: (A) with lines parallel to the applied field; and (B) with lines perpendicular to the magnetic field. Note the increase in slope as time increases. Since the slope change occurs for both orientations of magnetic field, it is likely not due to the increasing pattern width but due to clustering effects within the patterns, i.e., not pattern–pattern interaction; Panel (C) shows the average slope of the m-H curve obtained at 20 and 100 Oe as a function of coating time, and while at long times, the perpendicular field loops have a lower slope than the parallel loops, the error bars overlap and thus beyond the slope change due to increasing feature size that is isotropic with direction, no difference between parallel and perpendicular fields can be claimed from the data.

Mentions: Samples assembled for the same times as shown in Figure 1 and Figure 3 are pattern transferred to polymer films and mounted in two different orientations for magnetic characterization: grating lines perpendicular and parallel to the external field. Figure 6 A,B show normalized hysteresis loops for the five different coating times and different orientations. Interestingly, Figure 6A shows that the sample coated for 5 min has a smaller magnetic moment vs. magnetic field (mH) slope than the other four samples. As seen in Figure 6 A,B, the parallel and perpendicular m vs. H curves appear qualitatively similar. To determine whether there is a difference between parallel and perpendicular cases, the m vs. H curves were analyzed at low fields by fitting the linear part of the magnetization curves (the first term in a low-field expansion of the Langevin Equation is linear in magnetic field, i.e., for low fields L~a/3, where a = µ0mH/KbT, and µ0 is the permeability of free space, m the magnetic moment, H the magnetic field, Kb is Boltzmann’s constant and T is the temperature) [16,19]. Thus we fit the linear region of the curves in Figure 6 A,B with M/M0 = bH, where M0 is saturation magnetization, M is magnetization at each field H and b is the slope, µ0m/3KbT. Average values of b (slope) and standard deviations for perpendicular and parallel cases are shown in Figure 6C. While the perpendicular and parallel slopes are identical at short times, the perpendicular has a smaller slope than the parallel for longer times. However, the standard deviations in Figure 6C suggest this difference is not statistically significant.


Magnetic Nanoparticle Arrays Self-Assembled on Perpendicular Magnetic Recording Media.

Mohtasebzadeh AR, Ye L, Crawford TM - Int J Mol Sci (2015)

Magnetic moment as a function of external magnetic field for assembled nanoparticle patterns for different coating times measured: (A) with lines parallel to the applied field; and (B) with lines perpendicular to the magnetic field. Note the increase in slope as time increases. Since the slope change occurs for both orientations of magnetic field, it is likely not due to the increasing pattern width but due to clustering effects within the patterns, i.e., not pattern–pattern interaction; Panel (C) shows the average slope of the m-H curve obtained at 20 and 100 Oe as a function of coating time, and while at long times, the perpendicular field loops have a lower slope than the parallel loops, the error bars overlap and thus beyond the slope change due to increasing feature size that is isotropic with direction, no difference between parallel and perpendicular fields can be claimed from the data.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581324&req=5

ijms-16-19769-f006: Magnetic moment as a function of external magnetic field for assembled nanoparticle patterns for different coating times measured: (A) with lines parallel to the applied field; and (B) with lines perpendicular to the magnetic field. Note the increase in slope as time increases. Since the slope change occurs for both orientations of magnetic field, it is likely not due to the increasing pattern width but due to clustering effects within the patterns, i.e., not pattern–pattern interaction; Panel (C) shows the average slope of the m-H curve obtained at 20 and 100 Oe as a function of coating time, and while at long times, the perpendicular field loops have a lower slope than the parallel loops, the error bars overlap and thus beyond the slope change due to increasing feature size that is isotropic with direction, no difference between parallel and perpendicular fields can be claimed from the data.
Mentions: Samples assembled for the same times as shown in Figure 1 and Figure 3 are pattern transferred to polymer films and mounted in two different orientations for magnetic characterization: grating lines perpendicular and parallel to the external field. Figure 6 A,B show normalized hysteresis loops for the five different coating times and different orientations. Interestingly, Figure 6A shows that the sample coated for 5 min has a smaller magnetic moment vs. magnetic field (mH) slope than the other four samples. As seen in Figure 6 A,B, the parallel and perpendicular m vs. H curves appear qualitatively similar. To determine whether there is a difference between parallel and perpendicular cases, the m vs. H curves were analyzed at low fields by fitting the linear part of the magnetization curves (the first term in a low-field expansion of the Langevin Equation is linear in magnetic field, i.e., for low fields L~a/3, where a = µ0mH/KbT, and µ0 is the permeability of free space, m the magnetic moment, H the magnetic field, Kb is Boltzmann’s constant and T is the temperature) [16,19]. Thus we fit the linear region of the curves in Figure 6 A,B with M/M0 = bH, where M0 is saturation magnetization, M is magnetization at each field H and b is the slope, µ0m/3KbT. Average values of b (slope) and standard deviations for perpendicular and parallel cases are shown in Figure 6C. While the perpendicular and parallel slopes are identical at short times, the perpendicular has a smaller slope than the parallel for longer times. However, the standard deviations in Figure 6C suggest this difference is not statistically significant.

Bottom Line: This increase suggests magnetic nanoparticle interactions evolve from nanoparticle-nanoparticle interactions to cluster-cluster interactions as opposed to feature-feature interactions.We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media.If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials.

View Article: PubMed Central - PubMed

Affiliation: Smart State Center for Experimental Nanoscale Physics, Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA. ramoh87@gmail.com.

ABSTRACT
We study magnetic-field directed self-assembly of magnetic nanoparticles onto templates recorded on perpendicular magnetic recording media, and quantify feature width and height as a function of assembly time. Feature widths are determined from Scanning Electron Microscope (SEM) images, while heights are obtained with Atomic Force Microscopy (AFM). For short assembly times, widths were ~150 nm, while heights were ~14 nm, a single nanoparticle on average with a 10:1 aspect ratio. For long assembly times, widths approach 550 nm, while the average height grows to 3 nanoparticles, ~35 nm; a 16:1 aspect ratio. We perform magnetometry on these self-assembled structures and observe the slope of the magnetic moment vs. field curve increases with time. This increase suggests magnetic nanoparticle interactions evolve from nanoparticle-nanoparticle interactions to cluster-cluster interactions as opposed to feature-feature interactions. We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media. If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials.

No MeSH data available.