KURNIAWIDI, D.; SAPUTRA, K.; ARDIANTO, T.; INAYAH, R.; AMINY, I. UV-Vis Spectroscopic Analysis for Band Gap Determination of Cobalt-Doped Magnetite (Fe2.5Co0.5O4) Nanoparticles Derived from Natural Iron Sand. KONSTAN - JURNAL FISIKA DAN PENDIDIKAN FISIKA, v. 10, n. 2, p. 115-125, 21 maio 2026.