Reproducible manipulation of spin ordering in ZnCoO nanocrystals by hydrogen mediation

ZnO-based nanostructures for diluted magnetic semiconductor

“…Codoping of TM elements with excess hydrogen prepared through sol-gel has been used to investigate hydrogen-mediated ferromagnetism [43,64]. Electron paramagnetic resonance (EPR) studies on undoped and ZnO:(H,Mn) powder samples indicated the coupling of the shallow donors to the Mn ions, forming Mn-H AB -Mn complexes as a result, where H AB means stable hydrogen at an antibonding position.…”

The origin of ferromagnetism in Co-doped ZnO single crystalline films upon reducing annealings

“…However, ZnO is intrinsically n-type conducting and the p-type ZnO is difficult to realize experimentally [5]. In contrast to Mn-doped ZnO, Co-doped ZnO (ZnCoO) was theoretically predicated to become ferromagnetic with n-type doping [6] and a flood of experimental studies of this subject have been reported upon [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Despite RT ferromagnetism has been observed in Co-doped ZnO thin films and nanoparticles by many groups, there are still many controversies remaining on the physical origin and/or mechanism of the observed ferromagnetism.…”

“…Usually, the defects in ZnCoO, including Zn interstitials, O vacancies and H contamination, are easily generated or increased by annealing treatment in reducing atmosphere [21]. Recently, it has been reported that hydrogen treatment is the key factor to activate or enhance the high-temperature ferromagnetism in ZnCoO due to the enhancement of ferromagnetic spin-spin interactions by H mediation [13][14][15]. However, considering the fact that metallic Co may be easily reduced with hydrogen treatment, the possibility of a trace of Co segregations cannot be excluded in this system.…”

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

“…previous experimental studies using XRD, synchrotronscattering, neutron-scattering, and maximum entropy method (MEM) that the changes in the lattice constant by hydrogen injection were very small (strain: 0.02% (a-axis), 0.03% (c-axis)). 10,12 Although this small change in the lattice constant might contribute to a local lattice distortion in ZnCoO:H, it is unlikely that it could induce a large change in the carrier concentration.…”

“…[4][5][6][7][8] We and others proposed and demonstrated experimentally that ferromagnetism in ZCO is closely related to the hydrogen concentration. [9][10][11][12] Hydrogen dopants preferentially sit on the bond centers between Zn and O and Co and O, and act as shallow donors, generating electron carriers without affecting the spin ordering. When Co atoms are doped at high concentrations (>7%), a significant amount forms dimer structures.…”