Bias voltage dependence of magnetic tunnel junctions comprising double barriers and CoFe/NiFeSiB/CoFe free layer

다국어 초록 (Multilingual Abstract)

The typical double-barrier magnetic tunnel junction (DMTJ) structure examined in this paper consists of a Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO<SUB>x</SUB>/free layer/AlO<SUB>x</SUB>/CoFe 7/IrMn 10/Ru 60 (nm). The free layer consists of an Ni<SUB>16</SUB>Fe<SUB>62</SUB>Si<SUB>8</SUB>B<SUB>14</SUB> 7 nm, Co<SUB>90</SUB>Fe<SUB>10</SUB> (fcc) 7 nm, or CoFe t<SUB>1</SUB>/NiFeSiB t<SUB>2</SUB>/CoFe t<SUB>1</SUB> layer in which the thicknesses t<SUB>1</SUB> and t<SUB>2</SUB> are varied. The DMTJ with an NiFeSiB-free layer had a tunneling magnetoresistance (TMR) of 28%, an area-resistance product (RA) of 86 k Ω μm<SUP>2</SUP>, a coercivity (H<SUB>c</SUB>) of 11 Oe, and an interlayer coupling field (H<SUB>i</SUB>) of 20 Oe. To improve the TMR ratio and RA, a DMTJ comprising an amorphous NiFeSiB layer that could partially substitute for the CoFe free layer was investigated. This hybrid DMTJ had a TMR of 30%, an RA of 68 k Ωμ m<SUP>2</SUP>, and a H<SUB>c</SUB> of 11 Oe, but an increased H<SUB>i</SUB> of 37 Oe. We confirmed by atomic force microscopy and transmission electron microscopy that H<SUB>i</SUB> increased as the thickness of NiFeSiB decreased. When the amorphous NiFeSiB layer was thick, it was effective in retarding the columnar growth which usually induces a wavy interface. However, if the NiFeSiB layer was thin, the roughness was increased and H<SUB>i</SUB> became large because of the magnetostatic Ne´el coupling.