Hysteresis loop shift behavior of CoFeSiB amorphous ribbons
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Exchange bias phenomena of amorphous CoFeSiB ribbons have been probed at room temperature. The dramatic loop shift away from zero point occurred when the ribbons were annealed in ambient atmosphere with longitudinal field. The possible crystalline phases grown in our ribbons are discussed based on the grazing incidence diffraction and energy dispersive x-ray spectroscopy. The magnetic domain configuration of ribbon surface was also observed to make clear the dependence of bias behavior on the induced magnetic anisotropy in the ribbon. A simple phenomenological explanation was given to discuss the exchange bias in ribbons. I. INTRODUCTION
Cobalt-based amorphous alloys have gradually become best candidate of magnetic cores used in switched mode power suppliers and many magnetic sensors because of their superior soft magnetic properties compared with those of the traditional ferrites and permalloys.1,2 Usually, the convenient annealing process is an effective avenue to ameliorate their magnetically soft characteristic for special applications.3 However, sometimes the asymmetric hysteresis loops can be brewed up when the amorphous alloys were annealed in constant magnetic field.4,5 This abnormal magnetic property reminds us of the exchange bias (EB) behavior associated with the interface exchange coupling between ferromagnetic (FM) and antiferromagnetic (AFM) films,6,7 which is a really complex interaction in scale with atomic layers. Many scientists have contributed a large number of articles to demonstrate the coupling mechanism of two-dimensional materials. Some potential factors, such as thickness of FM and AFM layers, the roughness at interface, and grains size, have been emphatically probed to study their influence on the exchange coupling. Different from those multilayers, the ribbons spun out by a quenching technique rarely exhibit the distinct interface structures. Until now, the active discussion about the origin of EB in ribbons was so deficient that the detailed study associated with the microstructure characteristics of ribbons is necessary because this EB is still available in some particular applications (for instance: pulse transformer, magnetic amplifier). In this article, the EB behavior of the Co-based amorphous ribbons a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0185 J. Mater. Res., Vol. 24, No. 4, Apr 2009
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was systemically investigated. The microphase development, magnetic domains, and hysteresis loop properties are described to explain the possible source of this EB behavior. II. EXPERIMENTAL
Amorphous Co70Fe5Si15B10 ribbons were manufactured by a melt-quenching technique. The samples with approximately 10 mm wide and 30 mm thick were spun out at a wheel surface velocity of 25 ms1 in ambient atmosphere. These amorphous ribbons were annealed at different temperatures for several hours to ascertain the optimized magnetic properties. The magnetic field was used during annealing operation to p
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