Tunnel magnetoresistance for junctions with epitaxial full-Heusler Co_2FeAl_(0.5)Si_(0.5) electrodes with B2 and L2_1 structures

摘要

The tunnel magnetoresistance (TMR) effect has been investigated for magnetic tunnel junctions with epitaxial Co_2FeAl_(0.5)Si_(0.5) Heusler electrodes with B2 and L2_1 structures on a Cr-bufferd MgO substrate. The epitaxially grown Co_2FeAl_(0.5)Si_(0.5) has B2 structure when annealed below 400℃, and has L2_1 structure for annealing above 450℃. The TMR ratio of 76% at room temperature and 106% at 5 K were obtained for a MgO(001)/Cr/B2-type Co_2FeAl_(0.5)Si_(0.5)/Al oxide/ Co_(75)Fe_(25)/IrMn/Ta. The TMR ratio is larger than that of magnetic tunnel junction with an L2_1-type electrode, which may be due to the smoother surface of the B2 structure and disordered L2_1 structure due to the Cr atom interdiffusion.