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

Abstract

In this article we review the exotic magnetism of nanoparticles (NPs) formed by substances that are not magnetic in bulk as described with generality in Section 1. In particular, the intrinsic character of the magnetism observed on capped Au and ZnO NPs is analysed. X‐ray magnetic circular dichroism (XMCD) analysis has shown that the magnetic moments are intrinsic and lie in the Au and Zn atoms, respectively, as analysed in Section 2, where the general theoretical ideas are also revisited. Since impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states, the anomalous magnetic response is analysed in terms of the surface band in Section 3. Finally, Section 4 summarizes our last theoretical proposal.

Strong Paramagnetism of Gold Nanoparticles Deposited on aSulfolobus acidocaldariusSLayer

“…Therefore, recent models proposed to explain the magnetism in Au as from orbital origin, that consider quasifree electrons or holes [25,26] from the 6sp conduction band, or unpairing of quantumconfined conduction electrons excited thermally [27], cannot explain our experimental results.…”

Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

“…Both Zn and O vacancies have been suggested to be responsible for the induced magnetism [18,[60][61][62]. On the other hand, oxygen atoms on the polar ZnO surface can be spin polarized and undergo a long-range magnetic interaction [63][64][65]. in Fig.…”

Fluctuant magnetism in metal oxide nanocrystals capped with surfactants

“…Like in the case of ZnO NCs, the undoped and uncapped SnO 2 , TiO 2 , and CeO 2 NCs also show very weak FM after subtracting the diamagnetic background, which might arise from intrinsic defects such as oxygen vacancies. The above magnetism fluctuation with SC can be ascribed to an alteration of electronic configuration 10,13,14 induced by the electron transfer between NCs and surfactants, [18][19][20] which is revealed by the XPS spectra. The typical XPS spectra of ZnO and CeO 2 NCs before and after post-treating with TOPO, PVP, and PAA are shown in Fig.…”

“…4-5, compared with the functional O atoms of PAA, the functional P or N atoms of TOPO or PVP have relatively lower electronegativity and donate electrons to NCs more easily, thus leading to a larger Zn 2p 3/2 XPS peak shift towards low binding energies. The different NC-surfactant interactions should affect the kinetic energy as well as the interaction or coupling among the extra surface electrons donated by the capping surfactants, 18,19 thus lead to the different fluctuation rates of the NC magnetism with SC.…”

“…18,19 The above magnetism fluctuation of NCs with SC may arise from the variations of the number of electrons transferred to NCs from the capping surfactants. To confirm this, we performed the first-principle calculations of the spins in NCs with different numbers of extra electrons.…”