Evidence of intrinsic magnetism in capped ZnO nanoparticles

Abstract

We present here direct experimental evidence of the magnetic polarization of Zn atoms in ZnO nanoparticles capped with different materials by means of x-ray magnetic circular dichroism ͑XMCD͒. Our results demonstrate that the magnetism in this material is intrinsic and relays in the ZnO conduction band. The analysis of both x-ray absorption spectroscopy and XMCD signals points out the formation of a well-defined interface between ZnO and the capping molecule in which the exotic magnetism arises at the hybridized band formed among Zn and the bonding atom of the molecule. The magnetic properties of these systems should critically depend on the details of this interface which may offer a new insight into the different observations for seemingly identical materials.

Revisiting magnetism of capped Au and ZnO nanoparticles: Surface band structure and atomic orbital with giant magnetic moment

“…Chaboy et al [31] thoroughly studied the XAS and XMCD spectra of ZnO capped by organic molecules through N (amina) atoms. The formation of a well-defined interface between ZnO and the capping molecule was observed.…”

Emergent ferromagnetism in ZnO/Al2O3 core-shell nanowires: Towards oxide spinterfaces

“…[14][15][16][17][18][19][20] In terms of mechanism, alternation of the electronic configuration, which is often a consequence of either intentional or unintentional structural/chemical inhomogeneity introduced in sample synthesis, has been proven as a viable approach to induce ferromagnetism. [21][22][23] In particular, Coey et al proposed that shallow donor electrons can form spin-split impurity bands and bound magnetic polarons. 24 However, the main challenge remains regarding how to harness the oxide nanostructures to produce an enhanced and reliable magnetism in order to become relevant to practical spintronic devices.…”

“…Recently, engineering the ZnO surface has played important roles in modulating the spin polarization and magnetic order in several material systems including ZnO nanostructures with organic molecule-passivation. [21][22][23]25,29 In fact, Zn K-edge X-ray magnetic circular dichroism measurements revealed a ferromagnetic-like contribution from the interface formed between the ZnO nanoparticle core and the organic molecules. 23 Similarly, spontaneous magnetization and hysteresis were observed in ZnO nanowires (NWs) modified with thiol-capped Ag nanoclusters 30 and in ZnO/ZnS core-shell nanoparticles.…”

“…It is in line with the findings by Garcia et al, where capping ZnO nanoparticles with different organic molecules was found to induce room-temperature ferromagnetic-like behaviors. [21][22][23] In general, surfaces naturally break down the periodic boundary conditions which are assumed for ideal solids with infinite dimensions; thus, they are structural imperfection by themselves. Therefore, many structural motifs related to surfaces or grain boundaries can sustain a macroscopic magnetic order, particularly in nanomaterials.…”

Recent Progress of the X-ray Magnetic Circular Dichroism Technique for Element-Specific Magnetic Analysis

“…[94][95][96] Chaboy et al studied ZnO nanoparticles capped with different molecules using XMCD spectroscopy. 95,96) Figure 10 shows the XMCD results at the Zn L 2;3 and Zn K edges. No XMCD signal was observed at the Zn L 2;3 edges (2p !…”