Perpendicular exchange coupling effects in ferrimagnetic TbFeCo/GdFeCo hard/soft structures

Highlights: • Ferrimagnetic TbFeCo/GdFeCo hard/soft structures both with PMA are fabricated. • Exchange-spring and sharp switching in a step-by-step fashion are witnessed. • A perpendicular exchange bias field of several hundred Oersteds is observed. • The perpendicular exchange energy is determined to be in the range of 0.18–0.30 erg/cm². • The exchange energy is shown to increase with GdFeCo thickness in the bilayers. Bilayers consisting of magnetically hard TbFeCo and soft GdFeCo alloy were fabricated. Exchange-spring and sharp switching in a step-by-step fashion were observed in the TbFeCo/GdFeCo hard/soft bilayers with increasing GdFeCo thickness. A perpendicular exchange bias field of several hundred Oersteds is observed from the shift of minor loops pinned by TbFeCo layer. The perpendicular exchange energy is derived to be in the range of 0.18–0.30 erg/cm². The exchange energy is shown to increase with the thickness of GdFeCo layer in the bilayers, which can be attributed to the enhanced perpendicular anisotropy of GdFeCo layer in our experimental range.