Revisiting Fe/MgO/Fe(001): Giant tunnel magnetoresistance up to ~420% at room temperature

After the demonstration of the giant tunnel magnetoresistance (TMR) ratios at room temperature (RT) using a crystalline MgO barrier based magnetic tunnel junctions (MTJs) in 2004 [1] , [2] , an application range of spintronic devices, including read-heads of hard disk drives (HDDs) and cells of magnetoresistive random access memories (MRAMs), has been significantly boosted. Use of MgO barriers enabled to obtain large electric output from MTJ structures since a large TMR ratio over 100% can be easily achieved due to the ∆ 1 band preferential coherent tunneling mechanism [3] . Fe/MgO/Fe(001) is known as one of the most basic structures exhibiting the giant TMR effect [2] . The structure is very simple, and thus many theoretical calculations have been demonstrated so far [3] , [4] . However, experimental TMR ratios (180~220% at RT and 290-370% at low temperature) are much smaller than those of the predictions like >1,000%. In order to create novel MTJ-based applications, such as high-capacity MRAMs, magnetic logics, and brain-morphic devices, further improvement in an experimental TMR ratio is needed. Especially, it should be essential to understand the origin of the TMR gap between experiments and theories. In this study, we revisited the simplest "Fe/MgO/Fe(001)" MTJ to obtain much larger TMR ratios by careful tuning of growth conditions for all the layers, combining sputtering and electron-beam evaporation, and MgO barrier interface modifications [5] .