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Magnetic nanostructuring and overcoming Brown's paradox to realize extraordinary high-temperature energy products.

Balasubramanian B, Mukherjee P, Skomski R, Manchanda P, Das B, Sellmyer DJ - Sci Rep (2014)

Bottom Line: Here we achieve this goal in exchange-coupled hard-soft composite films by effective nanostructuring of high-anisotropy HfCo7 nanoparticles with a high-magnetization Fe65Co35 phase.An analysis based on a model structure shows that the soft-phase addition improves the performance of the hard-magnetic material by mitigating Brown's paradox in magnetism, a substantial reduction of coercivity from the anisotropy field.The nanostructures exhibit a high room-temperature energy product of about 20.3 MGOe (161.5 kJ/m(3)), which is a record for a rare earth- or Pt-free magnetic material and retain values as high as 17.1 MGOe (136.1 kJ/m(3)) at 180°C.

View Article: PubMed Central - PubMed

Affiliation: Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska, Lincoln, NE-68588 (USA).

ABSTRACT
Nanoscience has been one of the outstanding driving forces in technology recently, arguably more so in magnetism than in any other branch of science and technology. Due to nanoscale bit size, a single computer hard disk is now able to store the text of 3,000,000 average-size books, and today's high-performance permanent magnets--found in hybrid cars, wind turbines, and disk drives--are nanostructured to a large degree. The nanostructures ideally are designed from Co- and Fe-rich building blocks without critical rare-earth elements, and often are required to exhibit high coercivity and magnetization at elevated temperatures of typically up to 180 °C for many important permanent-magnet applications. Here we achieve this goal in exchange-coupled hard-soft composite films by effective nanostructuring of high-anisotropy HfCo7 nanoparticles with a high-magnetization Fe65Co35 phase. An analysis based on a model structure shows that the soft-phase addition improves the performance of the hard-magnetic material by mitigating Brown's paradox in magnetism, a substantial reduction of coercivity from the anisotropy field. The nanostructures exhibit a high room-temperature energy product of about 20.3 MGOe (161.5 kJ/m(3)), which is a record for a rare earth- or Pt-free magnetic material and retain values as high as 17.1 MGOe (136.1 kJ/m(3)) at 180°C.

No MeSH data available.


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Hf-Co nanoparticles.(a), Transmission electron microscope (TEM) image. (b), The corresponding particle-size histogram (d and σ/d are the average particle size and an rms standard deviation, respectively). (c), A high-resolution TEM image of a nanoparticle. (d), A high-angle annular dark-field (HAADF) image showing the Z (atomic number) contrast and the corresponding energy-dispersive x-ray spectroscopy (EDS) color maps, showing the color distributions for Co (red), Hf (blue), and combined Co and Hf. (e), An EDS line scan showing Co and Hf distributions across a nanoparticle (shown in the inset). (f), Room-temperature hysteresis loops measured along the easy- and hard-axis directions for an aligned nanoparticle film and for an isotropic nanoparticle film.
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f1: Hf-Co nanoparticles.(a), Transmission electron microscope (TEM) image. (b), The corresponding particle-size histogram (d and σ/d are the average particle size and an rms standard deviation, respectively). (c), A high-resolution TEM image of a nanoparticle. (d), A high-angle annular dark-field (HAADF) image showing the Z (atomic number) contrast and the corresponding energy-dispersive x-ray spectroscopy (EDS) color maps, showing the color distributions for Co (red), Hf (blue), and combined Co and Hf. (e), An EDS line scan showing Co and Hf distributions across a nanoparticle (shown in the inset). (f), Room-temperature hysteresis loops measured along the easy- and hard-axis directions for an aligned nanoparticle film and for an isotropic nanoparticle film.

Mentions: The next step is to control the particle size, composition, crystalline ordering, and easy-axis alignment of the Hf-Co nanoparticles to achieve suitable magnetic properties, especially a high coercivity, which is a precondition to use the nanoparticles as building blocks to fabricate exchange-coupled nanocomposites. Figure 1a shows a transmission-electron-microscope (TEM) image of the Hf-Co nanoparticles that we have used to fabricate our nanocomposites. The corresponding particle-size histogram, shown in Fig. 1b, yields an average particle size of about 12.7 nm with an rms standard deviation of σ/d ≈ 0.15. The Hf-Co nanoparticles are single-crystalline with a high degree of atomic ordering, as can be seen from the high-resolution TEM image in Fig. 1c.


Magnetic nanostructuring and overcoming Brown's paradox to realize extraordinary high-temperature energy products.

Balasubramanian B, Mukherjee P, Skomski R, Manchanda P, Das B, Sellmyer DJ - Sci Rep (2014)

Hf-Co nanoparticles.(a), Transmission electron microscope (TEM) image. (b), The corresponding particle-size histogram (d and σ/d are the average particle size and an rms standard deviation, respectively). (c), A high-resolution TEM image of a nanoparticle. (d), A high-angle annular dark-field (HAADF) image showing the Z (atomic number) contrast and the corresponding energy-dispersive x-ray spectroscopy (EDS) color maps, showing the color distributions for Co (red), Hf (blue), and combined Co and Hf. (e), An EDS line scan showing Co and Hf distributions across a nanoparticle (shown in the inset). (f), Room-temperature hysteresis loops measured along the easy- and hard-axis directions for an aligned nanoparticle film and for an isotropic nanoparticle film.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4151151&req=5

f1: Hf-Co nanoparticles.(a), Transmission electron microscope (TEM) image. (b), The corresponding particle-size histogram (d and σ/d are the average particle size and an rms standard deviation, respectively). (c), A high-resolution TEM image of a nanoparticle. (d), A high-angle annular dark-field (HAADF) image showing the Z (atomic number) contrast and the corresponding energy-dispersive x-ray spectroscopy (EDS) color maps, showing the color distributions for Co (red), Hf (blue), and combined Co and Hf. (e), An EDS line scan showing Co and Hf distributions across a nanoparticle (shown in the inset). (f), Room-temperature hysteresis loops measured along the easy- and hard-axis directions for an aligned nanoparticle film and for an isotropic nanoparticle film.
Mentions: The next step is to control the particle size, composition, crystalline ordering, and easy-axis alignment of the Hf-Co nanoparticles to achieve suitable magnetic properties, especially a high coercivity, which is a precondition to use the nanoparticles as building blocks to fabricate exchange-coupled nanocomposites. Figure 1a shows a transmission-electron-microscope (TEM) image of the Hf-Co nanoparticles that we have used to fabricate our nanocomposites. The corresponding particle-size histogram, shown in Fig. 1b, yields an average particle size of about 12.7 nm with an rms standard deviation of σ/d ≈ 0.15. The Hf-Co nanoparticles are single-crystalline with a high degree of atomic ordering, as can be seen from the high-resolution TEM image in Fig. 1c.

Bottom Line: Here we achieve this goal in exchange-coupled hard-soft composite films by effective nanostructuring of high-anisotropy HfCo7 nanoparticles with a high-magnetization Fe65Co35 phase.An analysis based on a model structure shows that the soft-phase addition improves the performance of the hard-magnetic material by mitigating Brown's paradox in magnetism, a substantial reduction of coercivity from the anisotropy field.The nanostructures exhibit a high room-temperature energy product of about 20.3 MGOe (161.5 kJ/m(3)), which is a record for a rare earth- or Pt-free magnetic material and retain values as high as 17.1 MGOe (136.1 kJ/m(3)) at 180°C.

View Article: PubMed Central - PubMed

Affiliation: Nebraska Center for Materials and Nanoscience and Department of Physics and Astronomy, University of Nebraska, Lincoln, NE-68588 (USA).

ABSTRACT
Nanoscience has been one of the outstanding driving forces in technology recently, arguably more so in magnetism than in any other branch of science and technology. Due to nanoscale bit size, a single computer hard disk is now able to store the text of 3,000,000 average-size books, and today's high-performance permanent magnets--found in hybrid cars, wind turbines, and disk drives--are nanostructured to a large degree. The nanostructures ideally are designed from Co- and Fe-rich building blocks without critical rare-earth elements, and often are required to exhibit high coercivity and magnetization at elevated temperatures of typically up to 180 °C for many important permanent-magnet applications. Here we achieve this goal in exchange-coupled hard-soft composite films by effective nanostructuring of high-anisotropy HfCo7 nanoparticles with a high-magnetization Fe65Co35 phase. An analysis based on a model structure shows that the soft-phase addition improves the performance of the hard-magnetic material by mitigating Brown's paradox in magnetism, a substantial reduction of coercivity from the anisotropy field. The nanostructures exhibit a high room-temperature energy product of about 20.3 MGOe (161.5 kJ/m(3)), which is a record for a rare earth- or Pt-free magnetic material and retain values as high as 17.1 MGOe (136.1 kJ/m(3)) at 180°C.

No MeSH data available.


Related in: MedlinePlus