Influence of glass insulation on the structure and magnetic properties of Co-Si-B microwires

Abstract

ABSTRACTInvestigations of the effect of glass insulation on the structure of Co67,7Fe4,3Cr3B15Si10 glass-coated microwire are carried out. It is shown that in initial MW the average distance between metal atoms and the average number of Co neighbors are 0.253 nm and 10.2, respectively. Heat treatments influence considerably on the structural parameters of amorphous microwires. In microwires, an increase in the height of the first maximum of the structure factor is observed, but in glass-coating microwires this increasing is more significant. Such structure changes indicate the beginning of crystallization processes. The crystallization of amorphous microwires occurs in two stages. At the first stage of crystallization primary α-Co crystallites are formed in residual amorphous matrix at the temperature 495 – 498°C. At the second stage the residual B and Si enriched amorphous phase transforms into Co2Si phase and the metastable phase Co3B through eutectic crystallization in the temperature range 510–550°C. The mean grain size and crystallized volume fraction of α-Co crystals are 20 nm and 7%, respectively. Additional internal stresses arising from the presence of glass insulation accelerate the crystallization processes (crystallized volume fraction and the mean grain size of Co crystals increases up to 12%, and 30 nm, respectively). The nanocrystalline structure cased a decrease of coercivity from 130 A/m in initial state to 60 A/m at the annealing 495°C.