Thickness effect on the easy axis distribution in exchange biased Co/IrMn bilayers

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Tarazona H.S.
Tafur M.
Quispe-Marcatoma J.
Landauro C.V.
Baggio-Saitovitch E.
Schmool D.S.
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Elsevier B.V.
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It is commonly assumed that in uncompensated FM/AF interfaces, the easy axes of antiferromagnetic grains are aligned toward the magnetic field direction applied during the film growth. However, due to several intrinsic and extrinsic factors, these easy axes can be aligned away from the unidirectional axis. In this context, the aim of this work is to study the relationship between the easy axes distribution (EAD) and thickness of both the ferromagnetic (FM) and antiferromagnetic (AF) layers in Co/IrMn bilayer systems. A phenomenological model for the free energy of the system that takes into account a domain wall formation in the AF layer and a Gaussian-type distribution of their easy axes is used. Thus, we simulate and fit the magnetization curves and get several magnetic parameters like rotatable anisotropy field, exchange bias field, coercivity and magnetic anisotropy. Our results show that when the AF thickness is increased, the width of the easy-axis distribution also increases following a power-law relationship. However, no correlation is observed when the FM thickness is varied. Furthermore, considering an easy-axis distribution we observe a significant reduction in coercivity as well as a slight decrease of the exchange bias field.
This work has been partially supported by the Brazilian agencies CNPq and FAPERJ. H. S. T. thanks to the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand #218-2014-FONDECYT. J. Q-M and C. V. L. are grateful to CIENCIACTIVA (CONCYTEC) for partial financial support through the Excellence Center Programs. J. Q-M is also grateful to the GEMaC Laboratory, for the hospitality during the preparation of this manuscript. In addition, E. B. S. acknowledges support from FAPERJ through several grants including Emeritus Professor fellow and CNPq for BPA and corresponding grants.
Palabras clave
Rotatable anisotropy, Antiferromagnetism, Coercive force, Domain walls, Film growth, Free energy, Frequency modulation, Antiferromagnetic grains, Domain wall formation, Easy axis, Exchange bias, Magnetic field direction, Phenomenological modeling, Power law relationship, Magnetic anisotropy