Role of Mg substitution in modulating defect-mediated magnetism and mechanical strength of Zn0.95Co0.05O systems

This study investigates the structural, magnetic, and mechanical modifications induced by partial Mg/Zn substitution in Zn_0.95Co_0.05O diluted magnetic semiconductor (DMS) systems prepared by the sol-gel method. A combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and Vickers microhardness (H_v) testing is employed to assess the impact of Mg incorporation. Experimental and computational results confirm the successful substitution of Mg²⁺ ions into the ZnCoO lattice without forming secondary phases. XRD analyses reveal a slight reduction in crystallite size, varying from 37.62 nm to 36.48 nm, attributable to the differences in ionic radius and electronegativity between Mg²⁺ and Zn²⁺ ions. Mg addition enhances crystallinity, interface state formation, and atomic-scale interactions, while promoting quantum confinement effects. SEM observations indicate that Mg/Zn substitution significantly influences particle size, surface morphology, and oxide layer thickness. Increasing Mg content improves grain coupling and surface uniformity through strengthened interfacial interactions. Microhardness results show that Mg incorporation improves mechanical stability by limiting crack propagation, enhancing grain boundary couplings, and minimizing stored internal strain energy. Magnetic measurements indicate that all samples exhibit predominantly paramagnetic behavior with weak ferromagnetic features emerging at low temperatures. Low-temperature magnetization is attributed to defect-mediated ferromagnetic coupling, whereas high-temperature behavior follows Curie–Weiss paramagnetism. The Mg/Zn substitution alters electronic structure and oxygen vacancy distribution, modulating exchange interactions. Small coercivity values (230 Oe in ZFC and 570 Oe in FC) and vertical M–H loop shifts at 5 K suggest diluted antiferromagnetism rather than conventional exchange bias effects. Additionally, creep analysis from loading–unloading curves confirms that increasing Mg content lowers the creep rate, with the ZnO: Mg (5%) sample exhibiting the best mechanical resilience. In conclusion, Mg substitution significantly enhances the structural, magnetic, and mechanical performance of ZnCoO matrices, making them more favorable for controlled paramagnetic applications than room-temperature spintronic technologies.

Graphical Abstract

Fundamental Structural Properties of Zn_0.95-xMg_xCo_0.05O DMS structure.