2362 IEEE TRANSACTIONS ON MAGNETICS, VOL. 33, NO. 3, MAY 1997 Magnetoelastic Behavior of Glass-Covered Amorphous Ferromagnetic Microwire J. Gonz´ alez, N. Murillo, V. Larin, J. M. Barandiar´ an, M. V´ azquez, and A. Hernando Abstract— Particular aspects concerning the magnetoelastic behavior of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 m) are reported about its as- prepared state as well as after various heating treatments. The main feature of such behavior is that related with the bistable behavior exhibited by this microwire. Magnetization process takes place by a single and large Barkhausen jump at a given applied field. For the as-prepared material, the value of this switching field 112 Am is about one order of magnitude larger than that reported for Fe-rich amorphous wires with diameter of about 125 m 8 Am . The effect of the thermal treatment as well as the stress dependence of for as- obtained and treated microwire are also reported and discussed in terms of the stress distribution within the microwire. Index Terms—Amorphous ferramagnetic microwire, magnetic bistability, magnetization process. I. INTRODUCTION I N RECENT years a good deal of interest has been devoted to the investigations of amorphous alloy wires with diam- eter typically of the order of 0.1 mm. Particularly interesting for technological applications is the low-field bistable behavior shown by iron-based amorphous wires associated with a “switching field” which makes them suitable for particular sensors [1]. The magnetization reversal process has been reviewed [2]. Along with these, the applied tensile stress dependence of magnetic parameters of the hysteresis loop, such as the switching field, , and reduced remanence for a highly magnetostrictive amorphous wire of diameter around 125 m, has been explained considering the stress distribution inside the wire which is connected to the different regions that were proposed for these amorphous wires. The effect of different agents (thermal treatments, external tensile stresses, length of the sample) on the bistable behavior of Fe Si B amorphous wire with a diameter of 125 m were reported in [3] and [4]. It was concluded that the experimental data on followed a law ( : applied tensile stress) for applied stresses larger than the internal Manuscript received September 10, 1994; revised January 10, 1996. This work was supported in part by the Spanish CICYT under Project MAT95/0273, MAT93/0437, and MAT93/0691 and by Excma Diputaci´ on Foral de Guip´ uzcoa. J. Gonz´ alez and N. Murillo are with the Departamento de F´ ısica de Materiales, Facultad de Qu´ ımica, Universidad del Pais Vasco, 20080 San Sebasti´ an, Spain. V. Larin is with “Amotec” S.R.L., Kishinev, 277038, Rep. Moldova. J. M. Barandiar´ an is with the Departamento de Electricidad y Electr´ onica, Universidad del Pais Vasco, 48080 Bilbao, Spain. M. V´ azquez and A. Hernando are with the Instituto de Magnetismo Aplicado RENFE-UCM, 28230 Las Rozas, Madrid, Spain. Publisher Item Identifier S 0018-9464(97)00672-9. ones. Consequently a nucleation mechanism was invoked for explaining such bistability in that wire. Glass-covered amorphous microwires are obtained by Tay- lor’s technique [4], [5]. General behavior concerning mechan- ical and magnetic properties was reported some time ago [8]–[10]. More recently some papers have been reported on their outstanding magnetic behavior [11]–[13]. The aim of the present paper has been the study of different aspects of the magnetization process of an Fe-rich amorphous wire of about 20 m in diameter covered by insulating glass having a diameter of about 2 m. The results will be compared with those obtained on an amorphous wire of nominal composition Fe Si B with 125 m diameter and without glass cover. Special attention will be paid to the switching process and to the effect of the thermal treatments and applied mechanical stresses. II. EXPERIMENTAL PROCEDURE (Fe Co ) Si B glass-covered amorphous wire was obtained by Taylor’s technique [5]–[7]. This method consists of drawing a glass pyrex-like tube containing the molten metal to a wire. Through this method, tiny wires can be obtained having a metallic nucleus covered by insulating pyrex-like coating. The diameter of metallic nucleus and the thickness of the coating are typically of a few microns. In the present work, experimental results are performed on wires having an amorphous FeCoSiB core of 20 m in diameter and an insulating coating of 2- m thick. The length of wire for measurements was 12 cm. These pieces were annealed at different temperatures ranging from 573 to 748 K for 1 h. Measurements of saturation magnetization and Curie tem- perature were performed in a Faraday magnetometer from room temperature up to 900 K in the high-field range (up to 1200 KAm ). DSC measurements (10 K/min) show two peaks of crystallization at about 833 and 883 K, respectively. The axial - hysteresis loop of the samples was obtained at room temperature by means of a conventional induction method at 50 Hz. It allows the determination of the switching field and the ratio remanence to saturation magnetization when magnetic bistability takes place. The magnetic field was applied by a Helmholtz-coil system producing a maximum field of 5 KAm . The data of and represent the average value of five measurements with a maximum deviation lower than 3% in all samples. The experimental set- up allowed us also to apply tensile and torsional strain on the samples. More details on this experimental set-up can be found in [4]. 0018–9464/97$10.00  1997 IEEE