NIMS Award Winner: William H. Butler,
Professor, Center for Materials for Information
An achievement in Materials Science and Technology:
“Theoretical prediction of giant tunnel magnetoresistance in Fe/MgO/Fe junction”
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.