IEEE Magnetics Society Distinguished Lecturer 2023
Magnetic Hardening in Low-Dimensional Ferromagnets
By: Dr. J. Ping Liu
Department of Physics, University of Texas at Arlington, Arlington, TX, USA
IEEE Magnetics Society Distinguished Lecturer 2023
How “hard” (coercive) a ferromagnet can be has been a puzzle for a century. Seven decades ago,
William Fuller Brown offered his famous theorem to correlate coercivity with the magnetocrystalline
anisotropy fields in ferromagnetic materials. However, the experimental coercivity values have been far
below the calculated levels given by the theorem, which is called Brown’s coercivity paradox.
Researchers have attempted to solve the paradox with sustained efforts; however, the paradox remains
unsolved, and coercivity still cannot be predicted and calculated quantitatively by modeling.
Progress has been made in the past 20 years in understanding coercivity mechanisms in nanoscale low-
dimensional ferromagnets. In fact, ferromagnetism is a size-dependent physical phenomenon, as
revealed by theoretical studies. However, nanoscale ferromagnetic samples with controllable size and
shape have been available only in recent times. By adopting newly developed salt-matrix annealing,
surfactant-assisted milling, and improved hydrothermal and chemical solution techniques, we used a
bottom-up approach to produce nanostructured magnets and have successfully synthesized
monodisperse ferromagnetic Fe–Pt, Fe–Co, and Sm–Co nanoparticles and Co nanowires with
extraordinary properties, which are strongly size- and shape-dependent. A study on size-dependent
Curie temperature of the L10 ferromagnetic nanoparticles with sizes down to 2 nm has experimentally
proved a finite-size effect. A systematic study of nanowires with extremely high coercivity above their
magnetocrystalline anisotropy fields has opened a door to the solution of Brown’s paradox.
Date and Time
Location
Hosts
Registration
- Date: 19 Jul 2023
- Time: 01:30 PM to 03:00 PM
- All times are (UTC-04:00) Eastern Time (US & Canada)
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- Toronto Metropolitan University
- Toronto, Ontario
- Canada
- Building: Kerr Hall
- Room Number: KHS 335
Speakers
Dr. J. Ping Liu
Magnetic Hardening in Low-Dimensional Ferromagnets
How “hard” (coercive) a ferromagnet can be has been a puzzle for a century. Seven decades ago,
William Fuller Brown offered his famous theorem to correlate coercivity with the magnetocrystalline
anisotropy fields in ferromagnetic materials. However, the experimental coercivity values have been far
below the calculated levels given by the theorem, which is called Brown’s coercivity paradox.
Researchers have attempted to solve the paradox with sustained efforts; however, the paradox remains
unsolved, and coercivity still cannot be predicted and calculated quantitatively by modeling.
Progress has been made in the past 20 years in understanding coercivity mechanisms in nanoscale low-
dimensional ferromagnets. In fact, ferromagnetism is a size-dependent physical phenomenon, as
revealed by theoretical studies. However, nanoscale ferromagnetic samples with controllable size and
shape have been available only in recent times. By adopting newly developed salt-matrix annealing,
surfactant-assisted milling, and improved hydrothermal and chemical solution techniques, we used a
bottom-up approach to produce nanostructured magnets and have successfully synthesized
monodisperse ferromagnetic Fe–Pt, Fe–Co, and Sm–Co nanoparticles and Co nanowires with
extraordinary properties, which are strongly size- and shape-dependent. A study on size-dependent
Curie temperature of the L10 ferromagnetic nanoparticles with sizes down to 2 nm has experimentally
proved a finite-size effect. A systematic study of nanowires with extremely high coercivity above their
magnetocrystalline anisotropy fields has opened a door to the solution of Brown’s paradox.
Biography:
J. Ping Liu (Fellow, IEEE) received his Ph.D. degree in physics from the University of Amsterdam,
Amsterdam, The Netherlands, in 1994. For the past four decades, he has worked in research and
development of permanent magnets and related magnetic materials in China, Europe, and USA. He is
currently a Distinguished University Professor with The University of Texas at Arlington, Arlington, TX,
USA. His current research has been focused on hard magnetic nanoparticles, thin films, and bulk
nanocomposites, as reported in his more than 320 peer-reviewed journal articles, review articles, and
books, including Nanoscale Magnetic Materials and Applications (Springer, 2009), Skyrmions:
Topological Structures, Properties, and Applications (CRC Press, 2016), and Permanent Magnets: The
History and Future (Science Press, 2020). He has supervised more than 50 graduate students and post-
doctoral researchers. Dr. Liu is an elected fellow of the American Physical Society. He received the
Outstanding Achievement Award at the 25th International Workshop on Rare-Earth and Future
Permanent Magnets and Their Applications in 2018.
Dr. J. Ping Liu
Magnetic Hardening in Low-Dimensional Ferromagnets
How “hard” (coercive) a ferromagnet can be has been a puzzle for a century. Seven decades ago,
William Fuller Brown offered his famous theorem to correlate coercivity with the magnetocrystalline
anisotropy fields in ferromagnetic materials. However, the experimental coercivity values have been far
below the calculated levels given by the theorem, which is called Brown’s coercivity paradox.
Researchers have attempted to solve the paradox with sustained efforts; however, the paradox remains
unsolved, and coercivity still cannot be predicted and calculated quantitatively by modeling.
Progress has been made in the past 20 years in understanding coercivity mechanisms in nanoscale low-
dimensional ferromagnets. In fact, ferromagnetism is a size-dependent physical phenomenon, as
revealed by theoretical studies. However, nanoscale ferromagnetic samples with controllable size and
shape have been available only in recent times. By adopting newly developed salt-matrix annealing,
surfactant-assisted milling, and improved hydrothermal and chemical solution techniques, we used a
bottom-up approach to produce nanostructured magnets and have successfully synthesized
monodisperse ferromagnetic Fe–Pt, Fe–Co, and Sm–Co nanoparticles and Co nanowires with
extraordinary properties, which are strongly size- and shape-dependent. A study on size-dependent
Curie temperature of the L10 ferromagnetic nanoparticles with sizes down to 2 nm has experimentally
proved a finite-size effect. A systematic study of nanowires with extremely high coercivity above their
magnetocrystalline anisotropy fields has opened a door to the solution of Brown’s paradox.
Biography:
J. Ping Liu (Fellow, IEEE) received his Ph.D. degree in physics from the University of Amsterdam,
Amsterdam, The Netherlands, in 1994. For the past four decades, he has worked in research and
development of permanent magnets and related magnetic materials in China, Europe, and USA. He is
currently a Distinguished University Professor with The University of Texas at Arlington, Arlington, TX,
USA. His current research has been focused on hard magnetic nanoparticles, thin films, and bulk
nanocomposites, as reported in his more than 320 peer-reviewed journal articles, review articles, and
books, including Nanoscale Magnetic Materials and Applications (Springer, 2009), Skyrmions:
Topological Structures, Properties, and Applications (CRC Press, 2016), and Permanent Magnets: The
History and Future (Science Press, 2020). He has supervised more than 50 graduate students and post-
doctoral researchers. Dr. Liu is an elected fellow of the American Physical Society. He received the
Outstanding Achievement Award at the 25th International Workshop on Rare-Earth and Future
Permanent Magnets and Their Applications in 2018.