Improvement in the voltage-controlled magnetic anisotropy effect by introducing an iridium diffusion-blocking layer

The demonstration of a large voltage-controlled magnetic anisotropy (VCMA) effect in polycrystalline magnetic tunnel junctions (MTJs) is an important technical challenge for realizing low-power spintronic devices, such as voltage-controlled magnetoresistive random access memory. In this study, in order to control the iridium concentration at the ferromagnet/dielectric interface, which is crucial to obtain the large VCMA effect, we have developed a magnetic tunnel junction (MTJ) structure incorporating an ultrathin MgFeO diffusion-blocking layer designed to suppress Ir diffusion. By inserting such an ultrathin MgFeO layer of only 0.15 nm thickness between the voltage-controlled ultrathin CoFeB and Ir doping layer, we observed a clear increase in the VCMA coefficient. We suggest that this acts by suppressing the deep diffusion of Ir atoms into the CoFeB layer during the deposition process. By optimizing the Ir doping concentration and the thickness of the MgFeO blocking layer, we achieved a maximum VCMA coefficient of −167 fJ/Vm in polycrystalline MTJs prepared by sputtering for a mass production process.