The 2,023rd Meeting of the Society

February 4, 1994 at 8:00 PM

Powell Auditorium at the Cosmos Club

The Silent Revolution

Rare Earth Permanent Magnets and Their Applications

Fred Rothwarf

Applied Technologies Enterprises, Ltd.

About the Lecture

Radical developments have recently occurred in the field of permanent magnet (PM) materials. The advent of rare earth permanent magnet (REPM) materials has increased the highest energy products, (BH)max, available by a factor of over five and raised the intrinsic coercivity, Hci by an order of magnitude. Consequently, a dramatic, rapid expansion of PM use is now taking place. This is leading to the miniaturization of conventional devices and the evolution of new applications and design concepts. This talk will review the new developments in REPM materials and discuss some of the potential applications such as energy storage, magnetic fluid conditioning, and magnetic resonance microscopy.

About the Speaker

Mr. Rothwarf earned an A.B. (Physics) in 1951, an A.M. (Physics) in 1953, and a Ph.D. (Solid State Physics) in 1960, all from Temple University. He completed postdoctoral studies in Superconductivity at the University of Paris, Orsay in 1966 under Professor P. G. DeGennes. He has worked at various U.S. Army laboratories and research offices as a solid state physicist and a Supervisory Materials Scientist. Mr. Rothwarf was the Materials Sciences Program Manager at the U.S. Army European Research Office from 1980 to 1984 and at the U.S. Army Research Office from 1984 to 1986. In 1984, he also co-founded the Advanced Materials Corporation. Mr. Rothwarf has served as Vice-President and Science Advisor for Virginia’s Center for Innovative Technology from 1988 to 1991. In 1989, he founded Applied Technology Enterprises, Ltd of which he is currently the president. He is also a Visiting Professor at Drexel University. Mr. Rothwarf currently has eleven patents and 67 publications.


The President, Ms. Enig, called the 2023th meeting to order at 8:15 p.m. on February 4, 1994. The Recording Secretary read the minutes of the 2022th meeting and they were approved. The President then read a portion of the minutes from the 415th meeting, February 3, 1894.

The President introduced Mr. Frederick Rothwarf of Applied Technology Enterprises, Ltd., who talked on “The Silent Revolution: Rare Earth Permanent Magnets and their Application".

Mr. Rothwarf began by remarking that Joseph Henry would have been very interested in the present developments in permanent magnets and superconducting materials. It was Joseph Henry and Michael Faraday who in 1831 independently investigated electromagnetic induction, the production of electric current in conductors exposed to a changing magnetic field.

The elements iron (Fe), cobalt and nickel, have atomic structures that give rise to a persistent electromagnetic moment. It has been found that when those elements are alloyed with rare earth elements such as neodymium (Nd) materials are produced that retain very strong, intrinsic magnetic fields. These alloys are the rare earth permanent magnets (REPM) such as Nd2Fe14B discovered in 1983 (boron, B). That alloy has a coercivity 10 times greater than previously available materials; that means it cannot be easily demagnetized except above its Curie temperature. It has a magnetic energy product 5 times greater than previously available materials; that means its magnetic field lines are tightly confined at the poles. It also has rigid magnetization vectors, that is, it retains its internal field in the presence of external magnetic fields. Such materials can be used as magnetic batteries, stores of magnetic energy.

In the 10 years since they were introduced, they have found many practical applications both because of the intense magnetic fields they are capable of producing and because of the further miniaturiztion they permit. They are now used in electromechanical devices such as motors and generators, in acoustic transducers such as speakers, earphones and ultrasonic generators, in mechanical force applications such as contact clamps, magnetic bearings and brakes, and balances, in electron and ion beam control devices such as microwave generators, wave guides, cathode ray tubes, mass spectrometers and particle accelerators, in medical applications such as nuclear magnetic resonance (NMR) imaging, mechanical prostheses, and hearing aids, and in such other devices as magnetic locks, electronic chokes and magnetic bubble computer memories. Some automobiles now use REPM's in 23 different applications. Another use now being investigated for automobiles is the electro-mechanical battery; these are fly wheel energy storage devices that can spin at 200,000 rpm and store approximately 0.9 kilowatt-hour. Mr. Rothwarf also discussed some of the marginal uses for REPM's that are not well understood, such as “fluid conditioning” in the extraction of oil, and the treatment of drinking water and gasoline.

Mr. Rothwarf then kindly answered questions from the audience.

The President thanked the speaker on behalf of the Society. There were no new members to be introduced. The President then announced that at next meeting on February 18, Mr. Michael H. Robinson of the National Zoological Park would talk on “The Crisis of Life on Earth and the Nature of Human Nature", made announcements concerning parking and transportation, and adjourned the 2023th meeting at 9:44 p.m.

Attendance: 62
Temperature: +5.7°C
Weather: overcast

Respectfully submitted,

John S. Garavelli
Recording Secretary