Induced moment due to perpendicular field cycling in trained exchange bias system
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c Indian Academy of Sciences
— journal of physics
Vol. 80, No. 4 April 2013 pp. 701–711
Induced moment due to perpendicular field cycling in trained exchange bias system AMITESH PAUL1,∗ and S MATTAUCH2 1 Technische
Universität München, Physik Department E21, James-Franck-Strasse 1, D-85748 Garching b. München, Germany 2 Jülich Centre for Neutrom Science Forschungszentrum Jülich GmbH, Außenstelle am FRM-II c/o TU München, Lichtenbergstraße 1, D-85747 Garching b. München, Germany ∗ Corresponding author. E-mail: [email protected] MS received 7 May 2012; revised 25 September 2012; accepted 8 October 2012 Abstract. Depth-sensitive polarized neutron scattering in specular and off-specular mode has recently revealed that perpendicular field cycling brings about a modification in the interfacial magnetization of a trained exchange coupled interface. We show here by various model fits to our neutron reflectivity data that a restoration of the untrained state is not possible in the case of our polycrystalline multilayer specimen. This is due to the magnetic moment at the interface induced only after perpendicular field cycling, changing the initial field-cooled state. Keywords. Neutron reflectometry; magnetic properties of interfaces. PACS Nos 61.05.fj; 75.70.Cn
Interfacial exchange coupling between a ferromagnet (FM) and an antiferromagnet (AF) can ‘lock’ the magnetization into the FM in a well-defined direction. This effect, which in a phenomenological picture takes the form of a unidirectional magnetic anisotropy, is known as exchange bias [1]. A cooling field HFC (cooling below the ordering temperature of AF) essentially determines the state of the FM which in turn determines the strength of the bias field HEB [2–4]. This exchange biasing demands a complete understanding [5] of various other related phenomena, such as coercivity enhancement [6,7], asymmetric hysteresis loops [2] and last but not the least, the training effect [8]. Difference between subsequent (partial) magnetization reversal loops is called the ‘training effect’. Even though the microscopic origin of the training effect is still under debate, it is generally agreed to be due to the rearrangement of interfacial AF spin structure, which can be considered as rotatable hysteretic grains (rotatable anisotropy) particularly in polycrystalline specimens [9,10]. Generally, a relatively large training is seen between the first and second hysteresis loops (and a comparatively small effect for the subsequent higher number of loops). The DOI: 10.1007/s12043-013-0508-5; ePublication: 15 March 2013
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Amitesh Paul and S Mattauch strong training behaviour between the first and second hysteresis loops is usually attributed to some initial non-equilibrium arrangement or metastable state of the AF spins. The exact mechanism for the initial AF spin arrangement is under debate. Brems et al [10] attempted to restore the untrained state. In their case the initial cooling field was applied sufficiently higher than the saturation field which in such circumsta
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