Strong ferromagnetism in Pt-coated ZnCoO: The role of interstitial hydrogen

Abstract

We observed strong ferromagnetism in ZnCoO as a result of high concentration hydrogen absorption. Coating ZnCoO with Pt layer, and ensuing hydrogen treatment with a high isostatic pressure resulted in a highly increased carrier concentration of 1021/cm3. This hydrogen treatment induced a strong ferromagnetism at low temperature that turned to superparamagnetism at about 140 K. We performed density functional method computations and found that the interstitial H dopants promote the ferromagnetic ordering between scattered Co dopants. On the other hand, interstitial hydrogen can decrease the magnetic exchange energy of Co-H-Co complexes, leading to a reduction in the blocking temperature.

Fabrication of ZnCoO nanowires and characterization of their magnetic properties

“…Unwanted hydrogen contamination during fabrication, in particular, is known to create defects that degrade the physical properties of ZnO-based materials. However, many experimental results have consistently supported the model of magnetic semiconductors in which Co-H-Co complexes are created by hydrogen doping of ZnCoO [5,13,16-21]. …”

Hydrogen lithography for nanomagnetic domain on Co-doped ZnO using an anodic aluminum oxide template

“…19,20 The reversible ferromagnetic-to-paramagnetic switching, as well as its higher T C value (which exceeds room temperature), suggested its potential for use in spin devices. [21][22][23][24][25][26][27] We speculated that the design of the ferromagnetic semiconducting pattern embedded in the ZnCoO semiconductor could be used as an integrated opto-spintronic device, thereby serving not only its main purpose as a magnetic semiconductor but also providing the means for rewritable information and display device operation manipulated by hydrogen. [28][29][30] In this study, we confirmed highly stable and reversible ferromagnetism controlled by hydrogen content and introduced a technique for designing localized ferromagnetic ordering in a paramagnetic ZnCoO semiconductor using hydrogen exposure of selected areas.…”

p-type conductivity generated by ferromagnetic ordering via percolative anionic H chain formation in ZnCoO

“…The ZnO based DMS has been theoretically predicted to be a room-temperature ferromagnet [2]. Following the first observation by Ueda et al [3], room-temperature ferromagnetism (FM) in Co-doped ZnO (ZnCoO) has been widely reported [4][5][6][7]. As distinct from predictions of hole-mediated FM in p-type material [2], FM is observed in n-type ZnCoO.…”

“…Zn 0.9 Co 0.1 O thin-films of 200 nm thickness were grown at 350 °C on Al 2 O 3 (0 0 0 1) and n-type Si(1 0 0) substrates via rf-magnetron sputtering. Pt films with thicknesses of 5-10 nm were deposited on the Zn 0.9 Co 0.1 O thin-films using a dc sputtering system in order to improve the hydrogen carrier density in the films via the spillover effect [7]. Hydrogen injection into the Pt-coated ZnCoO films was performed for 10 h at 300 °C under a pressure of 500 bar in a gas mixture of Ar:H 2 (ratio of 9 : 1 wt.%) using hot isostatic pressing (HIP).…”

“…Hydrogen injection into the Pt-coated ZnCoO films was performed for 10 h at 300 °C under a pressure of 500 bar in a gas mixture of Ar:H 2 (ratio of 9 : 1 wt.%) using hot isostatic pressing (HIP). The HIP process causes the hydrogen accumulated near the Pt layer to be dispersed into the thin-film sample [7,19] and the conditions of high temperature and high pressure aid the films to achieve a homogeneous and large carrier density. Further, these conditions also play a decisive role in the formation of stable injected-hydrogen sites in ZnCoO.…”