NIMS Award Winner: William H. Butler,
Professor, Center for Materials for Information
Technology (MINT),
An achievement in Materials Science
and Technology:
“Theoretical
prediction of giant tunnel magnetoresistance in Fe/MgO/Fe junction”
Curriculum vitae:
Prof.
William H. Butler was appointed as the Director of the
Brief introduction of Prof.
Butler’s achievements:
In magnetic
recording technology, writing and reading on magnetic media become increasingly
difficult as storage capacity increases. In particular, the reading technique
requires higher sensitivity and resolution, so magnetic tunnel junctions are
now being studied and have entered practical use. These junctions are also used
for non-volatile magnetic random access memory (MRAM). An amorphous insulator
such as Al2O3 was traditionally used for magnetic tunnel
junctions. However, Prof. Butler carried out a first-principles calculation for the tunneling transport through MgO(001) single-crystal
thin film, and theoretically predicted giant tunnel magnetoresistance (TMR) in the Fe/MgO/Fe (001) junction. Specifically, he predicted coherent
tunneling transport through the MgO(001) layer, which leads to the
giant TMR, increase in TMR with MgO thickness, oscillation of TMR as a function
of MgO thickness, etc. These results were reported in Physical Review B, 2001.
In succeeding years, both Dr. Yuasa of AIST and Dr. Perkin of IBM studied the
thin film system around almost the same time (2004), and reported giant
TMR of 180% and 220% at room temperature. These performances proved the validity
of Prof. Butler’s theoretical predictions, and TMR exceeding 500% has now been
achieved. This rapid improvement is expected to provide high functionality for
spintronics devices and lead to new applications. We recognize Prof. Butler’s outstanding
achievements which have
paved the way for breakthroughs in magnetic recording materials.