Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 27: Spinabh
ängiger Transport II

MA 27.7: Talk

Thursday, March 11, 2004, 16:45–17:00, H22

Magnetic tunnel junctions with CoFeB electrodes — •Theodoros Dimopoulos, Günter Gieres, and Joachim Wecker — Siemens AG, Corporate Technology, Erlangen

Amorphous ferromagnets are well known for their soft magnetic properties and they are used as cast ribbons e.g. in transformer cores for more than 20 years. Previous results have shown that indeed in magnetic tunnel junctions (MTJs) amorphous CoFeNiSiB detection layers show a low coercivity of about 2 Oe with a tunnel magnetoresistance (TMR) of about 22 % [1]. Here, we study the influence of amorphous CoFeB soft electrodes on the TMR and the tunneling characteristics (i.e. I(V) curves). Combined with crystalline CoFe as the hard electrode we find TMR signals as high as 51%. In contrast to MTJs with only crystalline electrodes we see a different dependence of the barrier parameters (height and thickness as extracted from fitting I(V) data with the Simmons model) on temperature. Using CoFeB also as the hard electrode (in this case pinned to IrMn) one can tailor the interfaces to get pure symmetric I(V) curves.

[1] A.Käufler et al., J.Appl.Phys. 91, 1701 (2002)