Bias voltage dependence of magnetic tunnel junctions comprising amorphous ferromagnetic CoFeSiB layer with double barriers

Doublebarrier magnetic tunnel junctions DMTJs with and without an amorphous ferromagnetic material such as CoFeSiB 10, CoFe 5CoFeSiB 5, and CoFe 10 nm were prepared and compared to investigate the bias voltage dependence of the tunneling magnetoresistance TMR ratio. Typical DMTJ structures were Ta 45Ru 9.5IrMn 10CoFe 7AlOxfree layer 10AlOxCoFe 7IrMn 10Ru 60 in nanometers. The interlayer coupling field and the normalized TMR ratios at the applied voltages of 0.4 and –0.4 V of the amorphous CoFeSiB freelayer DMTJ offer lower and higher values than that of the polycrystalline CoFe freelayer DMTJ, respectively. An amorphous ferromagnetic CoFeSiB layer improves the interface roughness of the free layertunnel barrier and, as a result, the interlayer coupling field and bias voltage dependence of the TMR ratio are suppressed at a given voltage. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim