Spin Reversal Mechanism of a Perpendicular Exchange Bias System with an Antiferromagnet Incorporating a Parasitic Ferromagnetism

Aluminum doping produced the parasitic magnetization (M_para) with high coercivity in 20 nm thin antiferromagnetic Cr₂O₃ films. By using the large coercive force of M_para, whose direction is the same as the antiferromagnetic Cr₂O₃ surface spin, antiferromagnetic spin reversal can be detected through the vertical shift of the hysteresis loop of an antiferromagnetic-Cr₂O₃/ferromagnet perpendicular exchange bias (PEB) coupling system. By analyzing both antiferromagnetic and ferromagnetic spin reversals in response to external magnetic field and temperature, each spin reversal mechanism in a PEB system is clarified. It is found that the competition among Zeeman energy due to M_para, exchange coupling energy, and antiferromagnetic anisotropy energy decides the antiferromagnetic spin direction and, accordingly, PEB sign under different cooling fields, different temperatures, and different swept magnetic fields for PEB systems. This work might contribute to a deep understanding of spin reversal mechanism in a perpendicular exchange bias system.