The influence of the magnetic history on the loop shift behavior of Fe-based amorphous ribbons
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X. Li School for Materials Science & Engineering, Beijing Institute of Technology, Beijing 100081, People’s Republic of China
B. Li and D.L. Zhao Division of Functional Material Research, Central Iron & Steel Research Institute, Beijing 100081, People’s Republic of China (Received 6 January 2010; accepted 5 May 2010)
The asymmetrical hysteresis loops were observed for the annealed Fe65Co15Si5B15 amorphous ribbons. The curves, which shift from the zero point of H axis with a unilateral step magnetization, exhibit the special magnetic features of the ribbons. A few magnetic crystalline phases were identified in the amorphous matrix of annealed ribbons by microstructure measurement. It was also found that the Z-oriented local magnetic domains emerge in the surface of ribbons with the loops shift behavior. Subsequent magnetic torque measurement indicated that the unidirectional magnetic anisotropy was induced in the amorphous ribbons with proper thermomagnetic annealing. These obtained evidences support our understanding that the magnetic history caused by thermomagnetic treatment plays a main role in promoting the formation of the asymmetrical loops.
I. INTRODUCTION
The hysteresis loops that shifted away from zero point was first discovered in oxide-coated Co particles by Meiklejohn and Bean in 1956.1 On the basis of the subsequent investigation in ferromagnetic and antiferromagnetic (FM/AFM) systems, a common explanation combined with the interfacial exchange interaction between the FM and AFM layer has been given to discuss their origin. Many factors, such as roughness, interface structure, and thickness, were thought to influence this shift in the multilayer film systems.2–4 The related theory and model about the aforementioned systems have been generally developed. Nearly three decades ago, few scientists ever mentioned that the Co-based amorphous ribbons can exhibit the displaced hysteresis curves along the positive or negative field direction.5,6 However, the characteristics of the shifted loops in the bulk ribbons are different from those in FM/AFM thin film systems. The shift field is only about 100 A/m for amorphous ribbons, dramatically lower than the scale of 105 A/m for an FMAFM system. On the other hand, the loop shift behavior in ribbons can easily occur at room temperature,5,7,8 but the behavior in FM/AFM systems has to be induced by a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0222
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 9, Sep 2010 Downloaded: 16 Mar 2015
cooling the sample below the Ne´el point of AFM materials in the magnetic field. Additionally, the atomic scale interface structure between FM and AFM layers is very important for FM/AFM systems to form the exchange bias phenomena. However, there are none of this kind of delicate interface features in the ribbons. Therefore, many groups have spent much effort to probe the mechanism of loop shift in ribbons.9–12 Different rough discussions were given to explain the as
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