Morphology-Dependent Room-Temperature Ferromagnetism in Undoped ZnO Nanostructures

Abstract

Since Dietl et al. predicted that Co-doped ZnO may show room-temperature ferromagnetism (RTFM) in 2000, researchers have focused on the investigation of ferromagnetic ZnO doped with various transition metals. However, after decades of exploration, it has been found that undoped ZnO nanostructures can also show RTFM, which in general is dependent on ZnO morphologies. Here, we will give an overall review on undoped ZnO nanomaterials with RTFM. The advanced strategies to achieve multidimensional (quasi-0D, 1D, 2D, and 3D) ferromagnetic ZnO nanostructures and the mechanisms behind RTFM are systematically presented. We have successfully prepared ferromagnetic nanostructures, including thin films, horizontal arrays and vertical arrays. The existing challenges, including open questions about quantum-bound ZnO nanostructures, are then discussed.

The Progress on Magnetic Material Thin Films Prepared Using Polymer-Assisted Deposition

“…Undoped ZnO nanostructures with RTFM were experimentally obtained through various methods, including sol-gel [ 84 , 85 , 86 ], pulsed laser deposition (PLD) [ 87 , 88 ], ball milling (BM) [ 89 , 90 ], PAD [ 29 , 43 , 44 , 71 ], electrochemical deposition method [ 91 ], chemical vapor deposition (CVD) [ 92 ], and ionic layer epitaxy (ILE) [ 64 ]. In general, the RTFM in ZnO is dependent on its morphology [ 21 , 43 , 44 , 71 ].…”

“…Although 2D zinc oxide [ 21 , 29 , 43 , 44 , 71 , 93 ] was not successfully grown using PAD, through unremitting efforts, Zou et al [ 2 ] obtained wafer-scale two-dimensional NiO TFs with RTFM in 2021. NiO is an intrinsic p-type semiconductor [ 180 , 181 ], and its bulk is an antiferromagnetism (AFM) [ 181 , 182 ] material.…”

“…Since polymer-assisted deposition (PAD) was proposed by Jia et al to prepare metal oxides in 2004 [ 1 ], it has been widely used in the preparation of various materials in many fields, including spintronics [ 2 , 3 , 4 ], energy storage and conversion [ 5 , 6 ], nuclear engineering [ 7 , 8 , 9 ], conformal coating [ 10 , 11 , 12 ], superconductivity [ 13 , 14 , 15 ], and optoelectronics [ 16 , 17 , 18 , 19 ]. PAD is a chemical synthesis method in which metal ions coordinated with polymers are used as the precursor, and then the polymer is removed at a high temperature (approximately 500 °C) [ 1 , 2 , 3 , 4 , 5 , 20 , 21 , 22 , 23 , 24 ]. Owing to the unique properties of its polymer-involved process, PAD has five main advantages: (1) it can realize wafer-scale preparation of materials [ 2 , 3 , 4 , 5 , 19 , 20 , 25 ]; (2) it can accurately adjust the thickness in the range of sub-nanometer thickness to a thickness of hundreds of nanometers [ 2 , 5 , 17 , 26 , 27 , 28 ]; (3) it is easy to produce materials doped with a variety of metal elements [ 29 , 30 , 31 ,…”

Strain-Modulated Magnetism in MoS2

“…Similar to ZnO [ 80 , 137 , 138 ] and graphene [ 4 , 10 ] NRs with zigzag-terminated edges, zigzag MoS 2 NRs also exhibit FM [ 17 , 80 ] independent of NRs width and thickness due to the edge atoms. In contrast, armchair NRs show non-magnetism (NM).…”

Strain Engineering of Intrinsic Ferromagnetism in 2D van der Waals Materials

“…After the discovery of the low-temperature, long-range ferromagnetic order in monolayers Cr 2 Ge 2 Te 6 and CrI 3 [ 7 , 8 ], many efforts have been made to achieve a room temperature (RT) ferromagnet. Indeed, strain engineering [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] is a very important strategy for mediating material properties, including optoelectronic [ 9 , 10 , 13 , 14 , 15 , 21 ], electrocatalytic [ 11 , 16 , 22 , 23 , 24 ], and magnetic properties [ 15 , 19 , 21 , 24 , 25 , 26 , 27 , 28 ]. Since Novoselov et al [ 29 ] obtained a stable monolayer graphene in the laboratory in 2004, further research gradually revealed that 2D materials, such as MoS 2 , could withstand up to 20% strain [ 30 , 31 , 32 , 33 ].…”