* Corresponding author. Fax: #091-657-270527. E-mail address: amitra@csnml.ren.nic.in (A. Mitra). Journal of Magnetism and Magnetic Materials 222 (2000) 263}270 Structural and soft magnetic properties of Fe  Nb  M  Si  B  (M"Cu, Mn, Pt) A.K. Panda, I. Chattoraj, A. Mitra* National Metallurgical Laboratory, Jamshedpur, India Received 28 March 2000; received in revised form 22 August 2000 Abstract The magnetic and the structural properties have been investigated for Fe  Nb  M  Si  B  (M"Cu, Mn, Pt) alloys in their as-received and heat-treated state. Di!erential scanning calorimeter and scanning electrical resistivity were used to study crystallization behaviour and to examine the in#uence of the nucleation elements Cu, Mn and Pt on the structural and magnetic properties of Fe-based nanocrystalline materials. The temperature coe$cient of resistivity above Curie temperature was found to be very low (0.210 K) in the Cu containing alloy as compared to the alloys which contained Mn or Pt. A broad exothermic DSC peak for the formation of Fe  Si nanoparticles was absent when Cu was replaced by Mn or Pt. Instead, a sharp exothermic peak for the formation of Fe  (SiB) phase was observed with an onset at 875 K. The magnetic properties of the three alloys measured after stress relaxed annealing were similar. However, after "rst-stage crystallization, the soft magnetic properties were further enhanced only in Cu containing alloys due to the formation of Fe  Si nanoparticles. Such nanoparticles together with di!erent intermetallic phases like FeMn  or FePt  were formed in Mn or Pt containing alloys. Moreover, the NbFeSi phase was also formed in the latter alloys after higher temperature annealing which reduced not only the amount of the Fe  Si phase but also the grain re"ning e!ect due to the lesser amount of Nb available at the grain boundary. When Cu was replaced by Mn or Pt, the formation of di!erent intermetallics reduced the volume fraction of Fe  Si nanoparticles and the lesser amount of grain re"ning Nb made the materials magnetically inferior after annealing above 775 K.  2000 Elsevier Science B.V. All rights reserved. Keywords: Nanocrystalline; Magnetic properties; Resistivity; Crystallization; Intermetallics 1. Introduction An important breakthrough was achieved by Yoshizawa et al. [1] with the introduction of Fe- based nanocrystalline alloys. This new generation of soft magnetic alloys are an extension of the Fe}Si}B glassy system with Cu and Nb as extra alloying elements. Annealing rapidly solidi"ed amorphous ribbons of these materials leads to the formation of nanosized Fe  Si grains embedded in an amorphous matrix [2,3]. The nanocrystalline formation is primarily attributed to the low solubil- ity of Cu ((0.2%) and Nb ((0.1%) in -Fe where Cu enhances nucleation of Fe  Si grains while Nb impedes grain coarsening. Hence, in the Fe}Nb}Cu}Si}B system, Cu and Nb play vital roles in producing the excellent soft magnetic prop- erties. In the quest to achieve properties superior to those of the well-known Fe}Nb}Cu}Si}B system, the element Nb had been substituted by Group 0304-8853/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 5 5 2 - 7