In 2001 Butler et al and Mathon et al independently made the theoretical prediction that using iron as the ferromagnet and MgO as the insulator, the tunnel magnetoresistance can reach several thousand percent. In 2004, Parkin et al and Yuasa et al were able to make Fe/MgO/Fe junctions that reach over 200% TMR at room temperature. In 2007, MgO based TMR devices completely displaced GMR devices on the magnetic storage device market.