IEEE TRANSACTIONS zyxwvutsrqponmlk ON MAGNETICS, VOL. 33, NO 5, SEPTEMBER 1997 3781 Structural and Magnetic Analysis of Amorphous Fe6,Co,,B1, Ribbons E.Ferrara, A.Infortuna, A.Magni and M.Pasquale IEN Galileo Ferraris, INFM zyxwvut and GNSM, zyxwvu C.so MdAzeglio 42, 10125 Torino, Italy zyxw Abstract - It is shown that the structural homogeneity and magnetic properties of Fe based amorphous alloys, quenched in different atmospheres, can be properly analyzed using the statistical theory of losses. A homogeneous microstructure can be obtained after etching and annealing treatments and then, according to the statistical theory of losses, only one microstructural parameter Vo is needed to describe the excess loss behavior of each sample. The dependence of this parameter Vo on atmosphere and treatment is discussed in terms of the quenched-in stress distribution. The analysis based on magnetic data is shown to be consistent with other structural informations obtained by DSC calorimetry and surface micrography. I. INTRODUCTION The connection between the magnetic characteristics of magnetostrictive amorphous alloys, surface irregularities and structural stress has been widely studied in the last twenty years. Detailed analysis of the effect of surface conditions and internal stress, induced by the rapid quenching, on the coercive field H, can be found in the literature [ 1-31. These studies can be connected to the analysis of dynamic losses since, in the case of thin (1 0-40 pm) soft materials excited at frequenciesfbetween 100 Hz and 100 kHz, the loss behavior can be greatly influenced by the excess loss component, connected to the interaction between domain walls, microstructure and surface conditions. The analysis and prediction of excess loss components can be performed using a statistical theory zyxwvutsr [4], using parameters which can be directly connected to the microstructural features. In this paper we show that, using the parameter zyxwvutsr Vo defined in the statistical theory of losses [4,5], a complete microstructural definition of amorphous Fe64C021B15 ribbons can be obtained. To this end three series of samples were melt spun in vacuum, Air and He atmosphere. Different structural conditions were obtained in connection with the different quenching rates and with the characteristics of the Fe,Co,,B,, alloy, which has a positive magnetostriction and is very sensitive to induced anisotropy [6]. Among the results we show that: a) the progressive stress relieving of the material, by etching or annealing treatments, can be analyzed using the parameter Vo. In particular, in the case of field annealed samples, only one constant value of Vo is sufficient to describe the loss behavior versus peak induction and frequency; b) in the vacuum-cast samples, appreciable stress relief can be obtained by etching. This shows that a small volume fraction near the wheel surface (-5%) contains most of the quenched in stresses [6]; c) Excess loss values described by Vo can be analyzed in terms of correlation lengths h = zyxwv d( Vo S) (5’ total sample cross section), obtaining h values which can be directly compared with those obtained in previous papers [5,8] on Fe and CO based amorphous alloys. This comparison indicates that high anisotropy values (greater than 1 kJ/m3) have been induced in the field annealed samples, a picture which is confirmed by the high frequency loss behavior and the observation of domain topologies with rigid, well separated, longitudinal walls. 11. EXPERIMENTAL 1) Sample Preparation: Amorphous Fe64Co,lB,5 alloy ribbons (-20 pm x 5 mm x 100 m) were produced with a planar flow casting apparatus in vacuum (-10 Pa), He (-lo5 Pa) and air, with a Cu(Zr) wheel rotating at a peripheral velocity of 30 m/s. Ribbons were cut in 300 mm sections for magnetic measurements and treatments. 2) Magnetic Characterization: To study the properties of the ribbons produced in different quenching environments, an extensive magnetic analysis was performed in the as quenched state, after annealing and after chemical etching. Hysteresis loop measurements for loss separation were Manuscript received January 31, 1997. M. Pasquale, +39-11-391-9751, fax +39-11-650-7611, pasquale@ien.it, http,//www.ien. it/ This work was supported in part by NATO under project HT-Linkage Grant no. 931575 Fig. 1. Total loss per cycle Plf on the field-annealed vacuum-cast sample, points measurements, lines prediction of the statistical theory of losses, parameters at all inductions rto=I, Vo= zyxw 9.I7. Inset measurements (points) of vacuum-cast as-cast sample, theory (lines) parameters at 1 T: no=I, Yo= 0.25.The zyxwvu 5 kHz measurements shows a strong deviation from fit (see text). 0018-9464/97$10.00 @ 1997 IEEE Authorized licensed use limited to: Istituto Nazionale di Ricerca Metrologica - INRIM. Downloaded on February 8, 2010 at 08:54 from IEEE Xplore. Restrictions apply.