The effects of magnetoelastically induced perpendicular anisotropy, K FM,me , on the perpendicular exchange bias ͑PEB͒ characteristics in ͓Pd/ Co͔ 5 / Fe 50 Mn 50 thin films have been explored by inserting ultrathin CoFe magnetic layers with different thicknesses, compositions, and Ar sputtering gas pressures ͑P Ar,CoFe ͒ at the interface between ͓Pd/ Co͔ 5 and FeMn. It was clearly found that the ͓Pd/ Co͔ 5 / CoFe/ FeMn with CoFe sputtered at a low P Ar,CoFe showed great enhancement in PEB due to the development of intrinsic compressive stress in the CoFe resulting in improving K FM,me and interfacial exchange coupling. Additionally, this effect was more significant for Co 80 Fe 20 insertion than Co 90 Fe 10 due to its larger magnetostriction.

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A physical model of perpendicular exchange bias (PEB) has been established based on the total energy equation per unit area of an exchange bias system by assuming coherent rotation of the magnetization. The anisotropy energy of antiferromagnetic (AFM) layer, KAFM×tAFM, as well as ferromagnetic (FM) multilayers, KFM,eff×tFM, and the interfacial exchange coupling energy, Jex were considered as primary physical parameters in building up the physical model of PEB phenomenon. It was proposed that the PEB is a result of the energy competition between KAFM×tAFM, KFM,eff×tFM, and Jex; where KAFM×tAFM≥Jex, is a critical condition to observe exchange bias in the system. In particular, it was revealed that Jex is directly relevant to the net magnetization of FM and AFM spin structure, Jex∝cos αAFM×cos βFM, in the perpendicular direction rather than the magnetization angle difference observed in an in-plane system. The physical role of perpendicular anisotropy energy, KFM,eff×tFM was also found to be significant to enhance the PEB. These physical characteristics are completely different from those are observed from an exchange bias system with in-plane anisotropy. The physical validity of the proposed PEB model was confirmed using different structures of exchange biased [Pd/Co]5/FeMn thin films with perpendicular anisotropy. The experimentally analyzed results demonstrated that the physical model of PEB proposed in this work is agreed well with the experimentally observed PEB phenomenon. Furthermore, the proposed model was found to be effective to design and to predict a new PEB system for the advanced spintronics applications.

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Exchange bias characteristics of [Pd/Co]5/FeMn thin films with perpendicular anisotropy have been explored by externally applying a mechanical stress for a magnetic pressure sensor application. It was found that the physical behavior of exchange bias field and coercivity of the [Pd/Co]5/FeMn thin films are closely relevant to the strength of applied stress and its direction. Magnetoelastic energy calculation and the physical analysis demonstrated that the stress-induced “Villari reversal” of the Co magnetizations directly resulted in changing the perpendicular anisotropy of the [Co/Pd] multilayers is primarily responsible for the variation in exchange bias coupling occurred at the [Co/Pd] and FeMn interface.