Tuning ferromagnetism in zinc oxide nanoparticles by replacing Zn2+ ions with Cr3+ ions D. Guruvammal, S. Selvaraj and S. Meenakshi Sundar Eur. Phys. J. Plus, 133 9 (2018) 347 Published online: 03 September 2018 DOI: 10.1140/epjp/i2018-12156-1