Mn掺杂ZnO薄膜的软X射线发射光谱研究

Soft X-ray Emission Spectra of Mn-doped ZnO Thin Films

利用先进光源(ALS)8.0.1光束线的软X射线荧光谱仪,对采用分子束外延(MBE)设备在200℃下生长的Zn0.97Mn0.03O和Zn0.67Mn0.33O薄膜样品进行了电子结构的研究.根据共振和非共振Mn L2,3边的X射线发射光谱,计算出Mn L2与Mn L3发射峰相对积分强度的比值(I(L2)/I(L3)),可知样品的铁磁性与自由d载流子的数目有关.在Zn0.97Mn0.03O中,Mn主要处于替代位置,并表现出较强的Coster-Kronig(C-K)跃迁效应,这说明样品中存在大量的自由d载流子.这些非局域的d载流子的行为类似于巡游电子,与Ruderman-Kittel-Kasuya-Yosid(RKKY)模型下计算得出的间隙Mn提供的4s电子,都可成为铁磁交换作用的媒介.在Zn0.67Mn0.33O中,自由d载流子的数目较少以及MnO团簇的存在是导致铁磁性向反铁磁性转变的主要原因.

The local electronic structures of Zn0.97Mn0.03O和Zn0.67Mn0.33O thin films prepared by a molecular beam epitaxy（MBE） at 200 ℃ were investigated by soft X-ray fluorescence spectrometer of beamline 8.0.1 of the Advanced Light Source（ALS）.The special interest can be given to find the relationship between the electronic structure of Mn and magnetic properties of our samples.Analysis of the integral intensity ratio of Mn L2 to L3 emission lines（I（L2）/I（L3）） from resonant and nonresonant Mn L2,3 X-ray emission spectra（XES） indicates that ferromagnetism（FM） is related to the free d charge carriers in the film.For ferromagnetic Zn0.97Mn0.03O sample,the majority of Mn atoms are incorporated at Zn substitutional sites and the film shows strong Coster-Kronig（C-K） transitions due to a large amount of free charge carriers available around Mn atoms.Both non-localized d charge carriers as itinerant electrons and 4s electrons from interstitial Mn obtained by Ruderman-Kittel-Kasuya-Yosid（RKKY） calculations can induce the ferromagnetic exchange interaction.However,the disappearance of FM in Zn0.67Mn0.33O sample can be explained in terms of the existence of MnO clusters leading to a reduction in the number of free charge carriers.