Magnetoelastic anisotropy distribution in glass-coated microwires
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Magnetoelastic anisotropy distribution in glass-coated microwires J. Vel´azquez, M. V´azquez, and A. P. Zhukova) Instituto de Magnetismo Aplicado, RENFE-UCM, and Instituto de Ciencia de Materiales, CSIC, P.O. Box 155, 28230 Las Rozas, Madrid, Spain (Received 8 September 1995; accepted 10 May 1996)
Amorphous microwires, obtained by the glass-coated melt-spinning method having diameters in the range of micrometers, can exhibit perfectly square (single and large Barkhausen jump) or quasi-anhysteretic hysteresis loops, depending on the easy magnetization direction determined by the intrinsic magnetoelastic anisotropy. The thermoelastic internal stressed frozen-in during the fabrication that model the domain structure are here calculated by considering the classical theory of elasticity. A complex stress distribution is obtained having magnitude of 103 MPa. Circular stresses turn out to be predominant, which arises from the composite nature of the microwire (metallic nucleus and insulating glass coating having different mechanical and thermal properties).
I. INTRODUCTION
Amorphous wires are most commonly prepared by the in-rotating-water quenching technique.1–3 This procedure implies a very high cooling rate from the molten alloy and gives rise to local magnetoelastic anisotropies arising from the coupling between internal stresses and magnetostriction. These anisotropies determine the domain structure and the hysteresis loop of the wire.4 The internal stresses are originated by the thermal gradient during quenching.5 The order of magnitude of these stresses is 102 MPa and is determined by Young’s modulus, Poisson’s coefficient, and by the average temperature during the fabrication.6 The technique of fabrication determines the diameter of the as-cast wires, which ranges between 70 and 160 mm when the amorphous structure is obtained. In contrast, glass-coated microwires are obtained by an extraction melt-spinning technique, based on Taylor’s classical method.7 The tiny dimensions and the outstanding magnetic behavior of these microwires make them very useful for practical purposes. The diameter of microwires is in the range of micrometers or tens of micrometers, and they consist of an amorphous metallic core covered by an insulating glass sheath. The coating process is developed during the fabrication process itself. A schematic view of the fabrication procedure is shown in Fig. 1. The metallic pellet that will constitute the metallic amorphous core of the microwire is placed inside a “pyrex”-like glass tube. A high frequency induction-coil furnace melts almost simultaneously both the metallic pellet and the glass tube. By a mechanical
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On leave from Institute of Solid State Physics of the Russian Academy of Sciences, 142432 Chernogolovka, Moscow, Russia. J. Mater. Res., Vol. 11, No. 10, Oct 1996
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rolling system, the wire is extracted, and a water jet cools the molten material. In this way, a very thin composite fi
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