Origin of the ferromagnetism in ZnCoO from chemical reaction of Co3O4

Seunghun Lee,Bum-Su Kim,조용찬,Jong-Moon Shin,Seung-Wan Seo,조채용,Ichiro Takeuchi,정세영 한국물리학회 2013 Current Applied Physics Vol.13 No.9

We investigated conversion of Co3O4 to Co nanoclusters through hydrogen reduction. Quantitativeanalysis is performed on the conversion of Co3O4 to Co metal as a function of hydrogen-injection conditions. Our results reveal that Co3O4 must be completely eliminated to avoid formation of the metalphase in ZnCoO. We also propose a new MeT curve based method for detecting nano-sized Co clusterswhich are below the detection limit of diffraction techniques. It is also found that the Co phase can betransformed back to the Co3O4 phase through oxygen annealing and that, as a result, the ferromagnetismcan be eliminated. These findings are discussed in the context of the origin of ferromagnetism in ZnCoO.

Origin of the ferromagnetism in ZnCoO from chemical reaction of Co₃O₄

Lee, S.,Kim, B.S.,Chan Cho, Y.,Shin, J.M.,Seo, S.W.,Cho, C.R.,Takeuchi, I.,Jeong, S.Y. Elsevier 2013 Current Applied Physics Vol.13 No.9

We investigated conversion of Co<SUB>3</SUB>O<SUB>4</SUB> to Co nanoclusters through hydrogen reduction. Quantitative analysis is performed on the conversion of Co<SUB>3</SUB>O<SUB>4</SUB> to Co metal as a function of hydrogen-injection conditions. Our results reveal that Co<SUB>3</SUB>O<SUB>4</SUB> must be completely eliminated to avoid formation of the metal phase in ZnCoO. We also propose a new M-T curve based method for detecting nano-sized Co clusters which are below the detection limit of diffraction techniques. It is also found that the Co phase can be transformed back to the Co<SUB>3</SUB>O<SUB>4</SUB> phase through oxygen annealing and that, as a result, the ferromagnetism can be eliminated. These findings are discussed in the context of the origin of ferromagnetism in ZnCoO.

Dependence of substrate temperature of Zn0.8Co0.2O films deposited by pulsed DC magnetron sputtering

김기출,Young-Hun Kang,Young-Sung Kim 한국물리학회 2008 Current Applied Physics Vol.8 No.6

We have investigated the microstructure, electrical and magnetic properties of the ZnCoO thin films, which were prepared by the asymmetrical bipolar-pulsed DC magnetron sputtering as a function of substrate temperature. The structural properties of ZnCoO films were characterized with a high resolution XRD. The XRD patterns of the ZnCoO films showed a strong (002) preferential orientation. The average crystallite size was 23–35 nm, which was estimated from full width at half maximum of XRD results. The electrical resistivity of the films were measured by the van der Pauw method through Hall measurement and showed below 10-1 X cm above 300 ˚C. The magnetic properties of the ZnCoO films were analyzed by the alternating gradient magnetometer at room temperature. All of the films were exhibited the ferromagnetic nature. The high conductivity and room temperature ferromagnetism of the ZnCoO films above 300 ˚C suggested that the possibility for the application to diluted magnetic semiconductors. We have investigated the microstructure, electrical and magnetic properties of the ZnCoO thin films, which were prepared by the asymmetrical bipolar-pulsed DC magnetron sputtering as a function of substrate temperature. The structural properties of ZnCoO films were characterized with a high resolution XRD. The XRD patterns of the ZnCoO films showed a strong (002) preferential orientation. The average crystallite size was 23–35 nm, which was estimated from full width at half maximum of XRD results. The electrical resistivity of the films were measured by the van der Pauw method through Hall measurement and showed below 10-1 X cm above 300 ˚C. The magnetic properties of the ZnCoO films were analyzed by the alternating gradient magnetometer at room temperature. All of the films were exhibited the ferromagnetic nature. The high conductivity and room temperature ferromagnetism of the ZnCoO films above 300 ˚C suggested that the possibility for the application to diluted magnetic semiconductors.

Fabrication of ZnCoO nanowires and characterization of their magnetic properties

Kim, Bum-Su,Lee, Seunghun,Kim, Won-Kyung,Park, Ji-Hun,Cho, Yong Chan,Kim, Jungdae,Cho, Chae Ryong,Jeong, Se-Young Springer 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1

<P>Hydrogen-treated ZnCoO shows magnetic behavior, which is related to the formation of Co-H-Co complexes. However, it is not well known how the complexes are connected to each other and with what directional behavior they are ordered. In this point of view, ZnCoO nanowire is an ideal system for the study of the magnetic anisotropy. ZnCoO nanowire was fabricated by trioctylamine solution method under different ambient gases. We found that the oxidation of trioctylamine plays an essential role on the synthesis of high-quality ZnCoO nanowires. The hydrogen injection to ZnCoO nanowires induced ferromagnetism with larger magnetization than ZnCoO powders, while becoming paramagnetic after vacuum heat treatment. Strong ferromagnetism of nanowires can be explained by the percolation of Co-H-Co complexes along the <I>c</I>-axis.</P>

Dependence of substrate temperature of Zn_0.8Co_0.2O films deposited by pulsed DC magnetron sputtering

Kim, K.C.,Kang, Y.H.,Kim, Y.S. Elsevier 2008 Current Applied Physics Vol.8 No.6

We have investigated the microstructure, electrical and magnetic properties of the ZnCoO thin films, which were prepared by the asymmetrical bipolar-pulsed DC magnetron sputtering as a function of substrate temperature. The structural properties of ZnCoO films were characterized with a high resolution XRD. The XRD patterns of the ZnCoO films showed a strong (002) preferential orientation. The average crystallite size was 23-35nm, which was estimated from full width at half maximum of XRD results. The electrical resistivity of the films were measured by the van der Pauw method through Hall measurement and showed below 10<SUP>-1</SUP>Ωcm above 300<SUP>o</SUP>C. The magnetic properties of the ZnCoO films were analyzed by the alternating gradient magnetometer at room temperature. All of the films were exhibited the ferromagnetic nature. The high conductivity and room temperature ferromagnetism of the ZnCoO films above 300<SUP>o</SUP>C suggested that the possibility for the application to diluted magnetic semiconductors.

Hydrogen shallow donors in Co-doped ZnO showing room-temperature ferromagnetism

Park, J.K.,Lee, K.W.,Noh, S.J.,Kim, H.S.,Lee, C.E. Elsevier 2014 Current Applied Physics Vol.14 No.2

<P>Room-temperature ferromagnetism has been identified in sol-gel-prepared Co-doped ZnO (ZnCoO), hydrogen being incorporated by a linear polymer polyvinyl pyrrolidone. The magnetic order was investigated by the X-ray photoemission and magnetization measurements in view of the interstitial hydrogen being coupled with Co2+. The electron paramagnetic resonance measurements revealed that hydrogens not contributing to the magnetic order occupy the shallow donor levels in the hydrogenated ZnCoO system. (C) 2013 Elsevier B.V. All rights reserved.</P>

Hydrogen shallow donors in Co-doped ZnO showing room-temperature ferromagnetism

박준규,이규원,노승정,김희수,이철의 한국물리학회 2014 Current Applied Physics Vol.14 No.2

Room-temperature ferromagnetism has been identified in solegel-prepared Co-doped ZnO (ZnCoO), hydrogen being incorporated by a linear polymer polyvinyl pyrrolidone. The magnetic order was investigated by the X-ray photoemission and magnetization measurements in view of the interstitial hydrogen being coupled with Co2þ. The electron paramagnetic resonance measurements revealed that hydrogens not contributing to the magnetic order occupy the shallow donor levels in the hydrogenated ZnCoO system.

증착온도를 달리하여 제조한 Zn_0.8Co_0.2O 박막의 미세조직 및 자기 특성

강영훈,김봉석,태원필,김기출,서수정,박태석,김용성,Kang, Young-Hun,Kim, Bong-Seok,Tai, Weon-Pil,Kim, Ki-Chul,Suh, Su-Jeung,Park, Tae-Seok,Kim, Young-Sung 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.2

We studied the microstructure and magnetic property of the pulsed DC magnetron sputtered $Zn_{\0.8}Co_{0.2}O$ film as a function of substrate temperatures. The X-ray patterns of the $Zn_{\0.8}Co_{0.2}O$ film showed a strong (002) preferential orientation at $500^{\circ}C$. The films with a crystallite size of 23-35 nm were grown in the form of nano-sized structure and this tendency was remarkable with increasing substrate temperature. The UV-visible result showed that the $Zn_{\0.8}Co_{0.2}O$ film prepared above $300^{\circ}C$ has a high optical transmittance of over $80\%$ in the visible region. The absorption bands were observed due to sp-d interchange action by $Co^{2+}$ complex ion and dd transition in the region from 500 to 700nm. The resistivity of the film was below $10^{-1}\;\Omega-cm\;above\;300^{\circ}C$. The AGM analysis results for the all films showed the magnetic hysteresis curves of ferromagnetic nature. The low electrical resistivity and room temperature ferromagnetism of ZnCoO thin films 'deposited above $300^{\circ}C$ suggested the possibility for the application to Diluted Magnetic Semiconductors (DMSs).

Local Structural Properties of Co-ion-implanted ZnO Nanorods

C.-I. Park,Zhenlan Jin,E.-S. Jeong,황인희,S. W. Han 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.11

We examined the local structural properties around Co and Zn ions in Co-ion-implanted ZnOnanorods by using an X-ray absorption fine structure (XAFS) analysis. Vertically-aligned ZnOnanorods were synthesized on Al2O3 substrates by using a catalyst-free metal-organic chemicalvapordeposition. Co ions (Co+ and Co2+) with energies of 50 and 100 keV and fluxes of 1013 and1015 particles/cm2 were implanted in the ZnO nanorods, and the ion-implanted ZnO nanorods wereannealed at 400 - 650C. X-ray absorption near edge structure (XANES) analyses demonstratedthat the chemical valence state of the Co ions were mostly 2+. An extended XAFS (EXAFS)analysis revealed that the Co ions were mostly substituted at the Zn sites of ZnO nanorods at a Coionflux of 1015 particles/cm2. However, at a flux of 1013 particles/cm2, Co ions formed Co-O andCo-Co clusters. These results were in contrast to the Co distribution in Co-added ZnO predictedby using a Monte Carlo method.

Distribution of Co Ions in Ferromagnetic Zn (1-x) Co (x)O Films

박창인,서수영,김정란,한상욱 한국진공학회 2012 한국진공학회 학술발표회초록집 Vol.2012 No.8