Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

【摘要】 Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H₂/Ar atmosphere with different H₂/Ar ratios.It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO.Mn ions initially enter into interstitial sites and a Mn³⁺O₆ octahedral coordination is produced in the prepared Mn-doped ZnO sample,in which the nearest neighbor Mn³⁺ and O² ions could form a Mn³⁺-O^2--Mn³⁺ complex.After H₂ annealing,interstitial Mn ions can substitute for Zn to generate the Mn²⁺O₄tetrahedral coordination in the nanocrystals,in which neighboring Mn²⁺ ions and H atoms could form a Mn²⁺-O^2--Mn²⁺complex and Mn-H-Mn bridge structure.The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn³⁺-O^2--Mn³⁺ complex,while the annealed samples exhibit their ferromagnetism,which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn²⁺-O^2--Mn²⁺complex.更多还原

【Abstract】 Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H₂/Ar atmosphere with different H₂/Ar ratios.It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO.Mn ions initially enter into interstitial sites and a Mn³⁺O₆ octahedral coordination is produced in the prepared Mn-doped ZnO sample,in which the nearest neighbor Mn³⁺ and O² ions could form a Mn³⁺-O^2--Mn³⁺ complex.After H₂ annealing,interstitial Mn ions can substitute for Zn to generate the Mn²⁺O₄tetrahedral coordination in the nanocrystals,in which neighboring Mn²⁺ ions and H atoms could form a Mn²⁺-O^2--Mn²⁺complex and Mn-H-Mn bridge structure.The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn³⁺-O^2--Mn³⁺ complex,while the annealed samples exhibit their ferromagnetism,which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn²⁺-O^2--Mn²⁺complex.更多还原