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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

High-temperature performance.(a), Temperature-dependent coercivity Hc and remanence Jr for Hf-Co nanoparticles. ΔHc and ΔJr denote the temperature coefficients in the temperature range of 27°C to 180°C. (b), The measured energy products (BH)max for nanocomposite films having different soft Fe-Co phase content f. (BH)max is the maximum value from the second quadrant of the BH curve (B = H + 4πM is the magnetic flux density). The dotted green rectangles in (a) and (b) mark the typical temperature region of 27 °C to 180 °C.
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f5: High-temperature performance.(a), Temperature-dependent coercivity Hc and remanence Jr for Hf-Co nanoparticles. ΔHc and ΔJr denote the temperature coefficients in the temperature range of 27°C to 180°C. (b), The measured energy products (BH)max for nanocomposite films having different soft Fe-Co phase content f. (BH)max is the maximum value from the second quadrant of the BH curve (B = H + 4πM is the magnetic flux density). The dotted green rectangles in (a) and (b) mark the typical temperature region of 27 °C to 180 °C.

Mentions: Permanent magnets often are required to operate above room temperature, for example at about 180 °C in high-performance motors, and it is important that remanent magnetic polarization Jr and coercivity Hc remain high at the operation temperature. The same applies to the energy product, a key figure of merit that describes the magnet's ability to store magnetostatic energy in free space12. Of crucial importance in this regard are the reversible temperature coefficients ΔJr = dJr/dT and ΔHc = dHc/dT of remanence and coercivity33. For example, Fig. 5a shows the measured values of Hc and Jr for Hf-Co nanoparticles as a function of temperature. The Hf-Co nanoparticles exhibit appreciable coercivities (from 8.65 to 4.5 kOe) and remanences (from 9.2 to 9.0 kG) for the temperature range of 27 °C to 180 °C. Note that Jr shows a slight increase to 9.2 kG at 450 K as compared to Jr = 9.1 kG (at 300 K) and Jr = 9.0 kG (at 400 K) and this variation is within the experimental error in magnetization. Figure 5a yields very low average temperature coefficients ΔJr ≈ −0.02%/°C and ΔHc ≈ −0.26%/°C for HfCo7 nanoparticles, which are far superior to the values obtained for the leading high-performance permanent-magnet material Nd2Fe14B (ΔJr = −0.10%/°C and ΔHc = −0.40%/°C)333435. This result can be attributed to the presence of about 87.5 at% of high Curie temperature Co in HfCo7 nanoparticles. Similar trends are found in the nanocomposites, such as high coercivities of 10.1 and 4.2 kOe (f = 0.07) and of 6.0 and 1.9 kOe (f = 0.22) in the temperature range of 27°C–180°C. Note that K1 decreases with increasing temperature, which further enhances δB and makes the nanostructuring more effective.


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)

High-temperature performance.(a), Temperature-dependent coercivity Hc and remanence Jr for Hf-Co nanoparticles. ΔHc and ΔJr denote the temperature coefficients in the temperature range of 27°C to 180°C. (b), The measured energy products (BH)max for nanocomposite films having different soft Fe-Co phase content f. (BH)max is the maximum value from the second quadrant of the BH curve (B = H + 4πM is the magnetic flux density). The dotted green rectangles in (a) and (b) mark the typical temperature region of 27 °C to 180 °C.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: High-temperature performance.(a), Temperature-dependent coercivity Hc and remanence Jr for Hf-Co nanoparticles. ΔHc and ΔJr denote the temperature coefficients in the temperature range of 27°C to 180°C. (b), The measured energy products (BH)max for nanocomposite films having different soft Fe-Co phase content f. (BH)max is the maximum value from the second quadrant of the BH curve (B = H + 4πM is the magnetic flux density). The dotted green rectangles in (a) and (b) mark the typical temperature region of 27 °C to 180 °C.
Mentions: Permanent magnets often are required to operate above room temperature, for example at about 180 °C in high-performance motors, and it is important that remanent magnetic polarization Jr and coercivity Hc remain high at the operation temperature. The same applies to the energy product, a key figure of merit that describes the magnet's ability to store magnetostatic energy in free space12. Of crucial importance in this regard are the reversible temperature coefficients ΔJr = dJr/dT and ΔHc = dHc/dT of remanence and coercivity33. For example, Fig. 5a shows the measured values of Hc and Jr for Hf-Co nanoparticles as a function of temperature. The Hf-Co nanoparticles exhibit appreciable coercivities (from 8.65 to 4.5 kOe) and remanences (from 9.2 to 9.0 kG) for the temperature range of 27 °C to 180 °C. Note that Jr shows a slight increase to 9.2 kG at 450 K as compared to Jr = 9.1 kG (at 300 K) and Jr = 9.0 kG (at 400 K) and this variation is within the experimental error in magnetization. Figure 5a yields very low average temperature coefficients ΔJr ≈ −0.02%/°C and ΔHc ≈ −0.26%/°C for HfCo7 nanoparticles, which are far superior to the values obtained for the leading high-performance permanent-magnet material Nd2Fe14B (ΔJr = −0.10%/°C and ΔHc = −0.40%/°C)333435. This result can be attributed to the presence of about 87.5 at% of high Curie temperature Co in HfCo7 nanoparticles. Similar trends are found in the nanocomposites, such as high coercivities of 10.1 and 4.2 kOe (f = 0.07) and of 6.0 and 1.9 kOe (f = 0.22) in the temperature range of 27°C–180°C. Note that K1 decreases with increasing temperature, which further enhances δB and makes the nanostructuring more effective.

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