AVS 53rd International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Paper MI-WeA3
All Ferromagnetic Exchange Bias Systems

Wednesday, November 15, 2006, 2:40 pm, Room 2006

Session: Exchange Bias & TMR
Presenter: A. Berger, Hitachi GST
Authors: A. Berger, Hitachi GST
D.T. Margulies, Hitachi GST
E.E. Fullerton, Hitachi GST
S. Polisetty, University of Nebraska
X. He, University of Nebraska
Ch. Binek, University of Nebraska
O. Hovorka, Drexel University
G Friedman, Drexel University
Correspondent: Click to Email
We have recently demonstrated a novel pathway for studying exchange bias and the tuning of hysteresis loop properties by combining two ferromagnetic layers with very different properties.@footnote 1@ Specifically, we use one hard ferromagnetic layer (HL) that serves as the tuning element, hereby replacing the antiferromagnetic layer of conventional exchange biased systems, and one soft ferromagnetic layer (SL) that is the actual tunable magnetic film. This bilayer structure has the advantage that the pre-set tuning field and temperature ranges are more accessible than in the case of traditional exchange bias structures using antiferromagnets. Also, a ferromagnetic HL allows for simple magnetometry monitoring of its magnetic state, which enables further insight into its role as the tuning element. The structures that were successfully utilized in our approach consist of a 15 nm thick hardmagnetic CoPtCrB-film, the tuning layer HL, exchange coupled by means of a 0.6 nm thick Ru-interlayer to a 1-2 nm thick CoCr-film, which is the tunable layer SL. We observe that the SL bias field h@sub bias@ is proportional to the HL magnetization M@sub r@, which suggests that the effective bias field is determined by the volume-averaged magnetization of HL. We also studied the existence of training effects in these all ferromagnetic exchange bias systems and found it to be triggered by the SL magnetization reversal.@footnote 2@ Furthermore, we were able to demonstrate experimentally for the first time that the amount of training in exchange bias systems is correlated with the HL magnetization state, in particular its distance from equilibrium@footnote 2@. @FootnoteText@ @footnote 1@A. Berger et al., Appl. Phys. Lett. 85, 1571 (2004)@footnote 2@Ch. Binek et al., Phys. Rev. Lett. 96, 067201 (2006).