First Principles Based Design and Experimental Evidence for a ZnO-Based Ferromagnet at Room Temperature

Abstract

The introduction of ferromagnetic order in ZnO results in a transparent piezoelectric ferromagnet and further expands its already wide range of applications into the emerging field of spintronics. Through an analysis of density functional calculations we determine the nature of magnetic interactions for transition metals doped ZnO and develop a physical picture based on hybridization, superexchange, and double exchange that captures chemical trends. We identify a crucial role of defects in the observed weak and preparation sensitive ferromagnetism in ZnO:Mn and ZnO:Co. We predict and explain co-doping of Li and Zn interstitials to both yield ferromagnetism in ZnO:Co, in contrast with earlier insights, and verify it experimentally.

Room-temperature ferromagnetism in Li-dopedp-type luminescent ZnO nanorods

“…Hole dopant Li Zn introduced at low synthesis temperature has been shown to promote long-range ferromagnetic coupling in ZnO:TM. 10 In the present case, dopant Li Zn is able to create ferromagnetic ordering in ZnO even in the absence of any 3d transition metal doping. DMS has been mostly observed in thin films.…”

“…This has the potential to harness magnetically controlled semiconducting light emitters. In a quest to find ferromagnetism in p-type ZnO without transition metal, as is preferable for spintronic applications, 10 doping of monovalent alkali atom Li with single unpaired spin in ZnO was undertaken. A combined study of electrical, magnetic, as well as structural and photoluminescence ͑PL͒ properties of Li-doped ZnO was carried out to explore ferromagnetism and to understand the physics.…”

Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

“…4 Here we report results of all-electron B3LYP ͑Refs. [15][16][17][18][19] and two of these 16,18 have considered the role of defects in promoting ferromagnetism. One of the difficulties in using DFT to study defects in an insulating material with defect-induced electronic states in midgap is severe underestimation of the band gap and overestimation of exchange coupling constants.…”

Carrier-mediated nonlocal ferromagnetic coupling between local magnetic polarons in Fe-doped In2O3and Co-doped ZnO

“…In contrast, the CTF model predicts that the moments are entirely localized on itinerant carriers confined to small regions possibly grain boundaries. 16 Although each model has its merits in certain aspects, [17][18][19][20][21][22][23][24][25][26] a complete understanding of the ferromagnetic behavior in oxide DMSs still calls for more microscopic insights into the defect structure, transport property, and moment distribution in these systems.…”