Hyperfine Interactions 27 (1986) 309-312 309 MAGNETIC PROPERTIES AND CRYSTALLISATION OF AMORPHOUS Fe 4ColoB16 ALLOY ANIL K. BHATNAGAR, B. BHANU PRASAD and R. JAGANNATHAN. University of Hyderabad, Hyderabad 500134, India. Magnetic properties and crystallization of amorphous Fe74Co10B16 have been investigated by MBssbauer and DSC measurements. Probabi- lity distribution of hyperfine field P(H) shows a single peak which shifts to lower fields with increase in temperature. Crystallization has been found to give rise to a-(Fe-Co), Fe2B and (Fe-Co)2B phases. 1. INTRODUCTION Random distribution of atoms in metallic glasses lead to a distribution in the exchange interactions, hyperfine fields, electric field gradients etc., and the resulting experimental observations are not well understood. On crystallization these glasses give rise to changes in their physical properties and so a temperature dependent study can reveal details of crystallization processes. Amorphous Fe74Co10BI6 is a high induc- tion magnetic material with potential for a wide variety of transformer and inductor core applications. We report here M~ssbauer and DSC studies of this material. A prelimi- nary MBssbauer study on this system has been reported earlier /1/. 2. EXPERIMENTAL Details of M}~ssbauer measurements and methods of analysis are described elsewhere /1]. Differential scanning Calorimetric (DSC) measurements were performed using a Perkin Elmer DSC-4 unit. X-ray measurements were taken on a Philips recording diffractometer. 3. RESULTS AND DISCUSSION M~Sssbauer spectra of "as received" Fe74Co10B16 were recorded between 80-670 K. The spectra showed characteristics typical of amorphous alloys as shown in Fig.1. One of the features in these spectra is the non-observance of amplitude or area asymmetries observed for many other metallic glasses /2/. This indicates that the effect of correlation between isomer shift and quadrupole splitting with hyperfine field and their consequent distribution in this alloy is less pronounced than in systems where such asymmetry has been reported /3[. M~Sssbauer spectrum at 665 K shown in Fig.l(D) gives a complex spectrum indicating that the crystallization temperature, Tx of the sample lies below its Curie temperature, Tc. An estimate of Tc by the extrapolation method described earlier /1/ gave a value of 760 K. The reduced hyperfine field, Heff(T)/Heff(O)~ vs reduced temperature, T/T c plot also showed deviations from the Brillouin curve typical of metallic glasses and attempts have been made to account for it by several workers /1,4,5/. Recently, Kane- yoshi and Tamura /5/ have suggested a modified form of Handrich model /1/ based on the distribution of magnetic moments and its temperature dependence to account for the observed deviations. However, it is found that our own empirical expression of the form d = ~o(l-t2) with t = T/T c /1/ fits the data closer particularly in the region 0.3 < TIT < 0.7. One possible reason for this can be the deviation of the suggested gaussian 9 9 . C distribution for the probability distribution function /1,5/ from the actual situation. 9 J.C. Baltzer A.G., Scientific Publishing Company