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Exploration of magnetic nanoparticle labels for giant magnetoresistance (GMR) biosensing technology is crucial because their characteristics determine GMR-based sensor performance, related to their stray field and compatibility to biomolecule. We investigated the potency of the green-synthesized magnetite (Fe₃O₄) nanoparticle as a green-magnetic label on a spin-valve (SV) GMR sensor based on a [Ta (2 nm)/Ir₂₀Mn₈₀ (10 nm)/Co₉₀Fe₁₀ (3 nm)/Cu (2.2 nm)/(Co₈₄Fe₁₀B₄ (10 nm)/Ta (5 nm)] structure that generated a 7.3 Oe exchange-bias field and 5.73% magnetoresistance. Fe₃O₄ nanoparticles were synthesized by a chemical coprecipitation method utilizing Moringa oleifera (MO) leaf extract as a natural reducing agent. The green-synthesized Fe₃O₄ nanoparticles exhibited a cubic inverse spinel structure as a pristine Fe₃O₄ characteristic. The crystallite size of green-synthesized Fe₃O₄ was larger than that …