Structural and magnetic properties of Nb substituted Zr-Co-Si-B nanocrystalline ribbons

The effect of large atomic radii Nb substitution on the structural and hard magnetic properties of Zr16Co78-xNbxSi3B3 nanocrystalline ribbons has been investigated. Structural and thermo-magnetic studies revealed that the substitution of Nb restrains the formation of both Co and orthorhombic Zr2Co11 phases in Zr-Co-Nb-Si-B which is essential for developing high coercivity. As a result, coercivity increases from 2.9 to 4.8 kOe as the Nb content increase from 0 to 3 at.%, while the magnetization decrease from 61 to 42 emu/g. The rhombohedral Zr2Co11 phase is responsible for the coercivity development in these materials. Substitution of Nb is found to decrease the Curie temperature from 440 to 390 °C as the Nb content increases from x = 0 to 3. Transmission electron microscopy studies demonstrate the grain refinement in the samples with substitution of Nb, where the grain size decreases from 150 to 50 nm as the Nb content increases from x = 0 to 3.