Room-Temperature Ferromagnetism Induced by High-Pressure Hydrogenation of ZnO

Abstract

In this work, we report direct evidence of ferromagnetism in hydrogenated ZnO sub-micrometric powders. Hydrogen (H2) was incorporated under a high-pressure heat treatment in a sealed reactor. Ferromagnetism at room temperature can be activated and deactivated by annealing in H2 and air atmospheres, respectively. Hydrogen incorporation in ZnO structure was observed from X-ray absorption near-edge structure spectra where hydrogen acts as a shallow donor transferring electrons to the conduction band (Zn 4s). The Raman measurements evidence clear distortions in chemical environments of Zn atoms associated with defect formation. Our results suggest that magnetism is a superficial phenomenon probably related to the surface bonding of hydrogen to Zn (or O) on polar ZnO surfaces.

On the Origin of d0 Magnetism in Transparent Metal Oxide Nanocrystals

“…33,57−59 Compared to colloidal NCs studied in this work, ZnO hydrogenation has been performed at much higher temperatures and/or under high hydrogen pressure. 59 More importantly, while the role of hydrogen in the ferromagnetism of ZnO has not yet been fully understood, lattice-incorporated hydrogen does not polarize either zinc or oxygen (conduction or valence band, respectively). 59 Furthermore, H has been found to produce a triplet state (S = 1) by coupling to the Zn vacancy, 60 which is also inconsistent with the magnetic field dependence of the excitonic MCD signal (vide infra).…”

“…59 More importantly, while the role of hydrogen in the ferromagnetism of ZnO has not yet been fully understood, lattice-incorporated hydrogen does not polarize either zinc or oxygen (conduction or valence band, respectively). 59 Furthermore, H has been found to produce a triplet state (S = 1) by coupling to the Zn vacancy, 60 which is also inconsistent with the magnetic field dependence of the excitonic MCD signal (vide infra). Nevertheless, we observed the presence of higher spin states (S > 1/2) in ZnO NCs synthesized in both reducing and oxidizing environments using magnetic susceptibility measurements (Figure S5).…”

“…High-Curie temperature ferromagnetism measured for Zn-rich ZnO films has, therefore, been ascribed to the Stoner model of ferromagnetism based on the charge-transfer processes . Electrical and magnetic properties of ZnO have also been discussed in the context of hydrogen incorporation. ,− Compared to colloidal NCs studied in this work, ZnO hydrogenation has been performed at much higher temperatures and/or under high hydrogen pressure . More importantly, while the role of hydrogen in the ferromagnetism of ZnO has not yet been fully understood, lattice-incorporated hydrogen does not polarize either zinc or oxygen (conduction or valence band, respectively) .…”

Morphology-Dependent Room-Temperature Ferromagnetism in Undoped ZnO Nanostructures

“…This promoted search for DMS based on alternative dopants. Manifestation of RTFM has also been undertaken by doping with non-magnetic dopants such as H [26,[98][99][100][101][102][103][104][105][106][107][108][109][110]124,125], N [126,127], C [128][129][130][131], and S [47,78]. Interestingly, the observation of RTFM strongly suggests the presence of a spin-split band with a non-zero spin-orbit coupling in H-ZnO single crystals [100].…”

Hypothesis on the Influence of the Magnetic Behaviour of Hydrogen Doped Zinc Oxide during Its Plasma Sputtering Process

“…Hydrogenated ZnO nanoparticles are reported to demonstrate ferromagnetism because due to low formation energies, the formation of Zn vacancies and OH bonding by hydrogen is favoured in the hydrogenation process, leading to a magnetic moment of ~0.57 μB (Bohr magneton), and the origin of ferromagnetism is explained through the hydrogenation of the ZnO polar surface [27,28].…”