Origin of variation of shift field via annealing at 400°C in a perpendicular-anisotropy magnetic tunnel junction with [Co/Pt]-multilayers based synthetic ferrimagnetic reference layer

We investigated properties of perpendicular-anisotropy magnetic tunnel junctions (p-MTJs) with [Co/Pt]-multilayer based synthetic ferrimagnetic reference (SyF) layer at elevated annealing temperature T a from 350°C to 400°C. Shift field H S defined as center field of minor resistance versus magnetic field curve of the MTJs increased with increase of T a from 350°C to 400°C. The variation of H S is attributed to the variation of saturation magnetic moment in the SyF reference layer. Cross sectional energy dispersive X-ray spectroscopy analysis revealed that Fe element of CoFeB in the reference layer diffuses to Co/Pt multilayers in the SyF reference layer.