Effects of heat treatment on nanocrystalline formations in Fe<inf>40</inf>Ni<inf>40</inf>(Si + B)<inf>19</inf>Mo<inf>1-2</inf>amorphous ribbon

Abstract

Effects of heat treatment on Fe40Ni40(Si + B)19Mo1-2were monitored by Mössbauer spectroscopy (MR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Mössbauer spectra were fitted by using the PC-MOS II program to obtain such parameters as hyperfine field, isomer shift and quadrupole splitting of samples annealed for two hours in argon at different temperatures. The change in direction of local magnetization and the transformation of amorphous to crystalline phase were observed. Heat treatments near the crystallization temperature between 450-500°C resulted in nanograins of α-Fe, α-Fe(Si) and t-Fe2B embedded in the remaining uncrystallized amorphous matrix. DSC data showed that the ribbon exhibited two-step crystallizations at 454°C and 525°C, respectively. The first crystallization corresponded mainly to soft ferromagnetic α-Fe, α-Fe(Si) and some minor t-Fe2B phase formations, while the second, corresponded to t-Fe3B phase. Further heat treatment at 600°C led to complete crystallizations at which the ferromagnetic phases α-Fe and α-Fe(Si) transformed to a paramagnetic phase fcc-FeNi, and ferromagnetic phases of c-FeNi3, t-Fe2B, t-Fe3B, and Ni2Si, respectively. Due to the high mag-netic anisotropy of t-Fe2B and other phases as well as to keep the crystallites in the nano region, the Fe40Ni40(Si-B)19Mo1-2ribbon should not be heated above 500°C for the superior magnetic properties. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.