Structural and magnetic properties of nanocrystalline Zr-Co-Nb-Si-B rare earth free permanent magnets fabricated by spark plasma sintering

•SPS was successfully employed to fabricate Zr16Co78-xNbxSi3B3 bulk magnets.•Phase decomposition was not observed after SPS due to low temperature sintering.•SPS temperature and Nb content are influencing resultant magnetic properties.•Optimum magnetic properties were obtained for x = 1 magnet consolidated at 600 °C. Rare earth free nanocrystalline Zr16Co78-xNbxSi3B3 (x = 0–3) bulk magnets were fabricated from melt spun ribbons with high density by employing spark plasma sintering (SPS) technique. The effect of SPS temperature on structural and magnetic properties was investigated. The hard magnetic Zr2Co11 phase which was present in the as-spun ribbons retained after SPS, indicating no phase decomposition. The magnetic properties were found to depend on consolidation temperature and Nb concentration. Optimum magnetic properties of coercivity of 3.3 kOe with saturation magnetization of 52 emu/g were obtained for x = 1 magnet consolidated at 600 °C. SPS magnets display a moderate magnetic texture and the coercivity mechanism is governed by combination of both domain wall pinning and nucleation of reverse domains.