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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.


Related in: MedlinePlus

Exchange-coupled nanocomposites.(a), A schematic of the nanocomposite sample showing the dispersion of the easy-axis aligned Hf-Co nanoparticle-structures in a Fe-Co film. (b), Room-temperature hysteresis loops for Hf-Co:Fe-Co having different Fe-Co contents f.
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f3: Exchange-coupled nanocomposites.(a), A schematic of the nanocomposite sample showing the dispersion of the easy-axis aligned Hf-Co nanoparticle-structures in a Fe-Co film. (b), Room-temperature hysteresis loops for Hf-Co:Fe-Co having different Fe-Co contents f.

Mentions: The STEM results suggest that the structure of the Hf-Co:Fe-Co nanocomposite films is similar to the schematic picture of Fig. 3a. In this nanostructure, the easy-axis aligned Hf-Co nanoparticles are dispersed in an Fe-Co matrix. Except for fields near Hc, the magnetization of the soft phase is parallel to the easy axis of the aligned hard nanoparticles, due to effective exchange coupling. This magnetic structure is confirmed by the room-temperature hysteresis loops measured along the easy-axis direction for the nanocomposite films. Figure 3b shows single-phase in-plane hysteresis loops for all considered volume fractions of the soft phase. A weak kink observed near H = 0 in the second quadrant of the hysteresis loops indicates the magnetization-reversal of the soft Fe-Co phase, originating from a weak decoupling between the soft and hard phases. The nanocomposites having f = 0.07 and f = 0.22 also exhibit high remanence ratio Mr/Ms = 0.90, as compared to Mr/Ms = 0.82 for bare Hf-Co nanoparticles. Like aligned HfCo7 nanoparticles, the aligned nanocomposite films also show high easy-axis Hc and Mr/Ms as compared to Hc and Mr/Ms measured along the hard-axis direction (Fig. S6 in Supplementary Information). Note that the room-temperature initial magnetization curves also were measured along the easy-axis direction for Hf-Co and Hf-Co:Fe-Co nanocomposite films and the results reveal a nucleation-type coercivity mechanism (Fig. S7 in Supplementary Information).


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)

Exchange-coupled nanocomposites.(a), A schematic of the nanocomposite sample showing the dispersion of the easy-axis aligned Hf-Co nanoparticle-structures in a Fe-Co film. (b), Room-temperature hysteresis loops for Hf-Co:Fe-Co having different Fe-Co contents f.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Exchange-coupled nanocomposites.(a), A schematic of the nanocomposite sample showing the dispersion of the easy-axis aligned Hf-Co nanoparticle-structures in a Fe-Co film. (b), Room-temperature hysteresis loops for Hf-Co:Fe-Co having different Fe-Co contents f.
Mentions: The STEM results suggest that the structure of the Hf-Co:Fe-Co nanocomposite films is similar to the schematic picture of Fig. 3a. In this nanostructure, the easy-axis aligned Hf-Co nanoparticles are dispersed in an Fe-Co matrix. Except for fields near Hc, the magnetization of the soft phase is parallel to the easy axis of the aligned hard nanoparticles, due to effective exchange coupling. This magnetic structure is confirmed by the room-temperature hysteresis loops measured along the easy-axis direction for the nanocomposite films. Figure 3b shows single-phase in-plane hysteresis loops for all considered volume fractions of the soft phase. A weak kink observed near H = 0 in the second quadrant of the hysteresis loops indicates the magnetization-reversal of the soft Fe-Co phase, originating from a weak decoupling between the soft and hard phases. The nanocomposites having f = 0.07 and f = 0.22 also exhibit high remanence ratio Mr/Ms = 0.90, as compared to Mr/Ms = 0.82 for bare Hf-Co nanoparticles. Like aligned HfCo7 nanoparticles, the aligned nanocomposite films also show high easy-axis Hc and Mr/Ms as compared to Hc and Mr/Ms measured along the hard-axis direction (Fig. S6 in Supplementary Information). Note that the room-temperature initial magnetization curves also were measured along the easy-axis direction for Hf-Co and Hf-Co:Fe-Co nanocomposite films and the results reveal a nucleation-type coercivity mechanism (Fig. S7 in Supplementary Information).

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