"Green Magnetic Energy: Exchange Coupled Nanomagnetss"
Dr. Yang-Ki Hong
Magnetic Materials and Device Laboratory
Department of Electrical and Computer Engineering and Materials Science Ph.D. Program, The University of Alabama,Tuscaloosa
The figure of merit for permanent magnet is the maximum energy product (BH)max in the units of MGOe. Sintered Nd2Fe14B and SmCo magnets show high 64 and 28 MGOe of theoretical (BH)max, respectively. However, low operation temperature of NdFeB, which may lead to loss of machine power, and availability of rare-earth elements are potential barriers to the electric vehicle's motor and other applications. Thus, aiming at developing high-temperature magnet without the rare-earth element, we have theoretically calculated the (BH)max for MnBi and t-phase MnAl alloys and their core-shell nanomagnets using density functional theory and modified Skomski's equation. Our calculations predict 20 MGOe (3.66 ÁB/f.u.; Hk = 53 kOe) and 12.5 MGOe for MnBi and MnAl alloys, respectively. Accordingly, it is envisioned that core (hard) - shell (soft) nanomagnet will exhibit large remnant magnetization, thereby increasing the (BH)max to 51 MGOe and 53 MGOe for MnAl and MnBi core-shell nanomagnet, respectively. This is attributed to magnetic exchange coupling at the interface between hard-core and soft-shell. Electron microscopic characterization of the interfacial atomic structure between hard and shell ferromagnets will lead to further understanding of exchange magnetic coupling in high (BH)max core-shell nanomagnet.
Dr. Yang-Ki Hong is the E. A. "Larry" Drummond Endowed Chair Professor of Department of Electrical and Computer Engineering and Professor of Materials Science Ph.D. Program, The University of Alabama, Tuscaloosa, AL. He received his Ph.D. in Metallurgy from University of Utah in 1981 and received BS and MS (Magnetism and Mossbauer spectroscopy) in Physics from Yonsei University, Seoul, South Korea. He completed the Program for Management Development (PMD) of Graduate School of Business Administration, Harvard University in 1992. Dr. Hong has received 13 patents on “Pac-Man” magnetic elements for MRAM, barium ferrite nanoparticles for data storage, barium trontium titanate nanoparticles for capacitors, and others. He has authored or co-authored more than 100 refereed journal papers and presented more 170 papers at conferences, symposia, and technical meetings.