釤鍶錳氧薄膜之電子結構以及X光吸收能譜學研究

Abstract

釤鍶錳氧(Sm1-xSrxMnO3)是一種鈣鈦礦結構的化合物，而特別的是Sm1-xSrxMnO3會隨著不同的摻雜比例而呈現出不同的磁性相變以及有序排列。 過渡金屬氧化物在現代磊晶技術的進步之下，我們可以透過成長不同薄膜厚度的樣品以及運用基板應力去影響錳的3d電子軌域排列。因此我們運用X光繞射技術去量測薄膜的晶體結構以及透過X光線性二向性吸收能譜探究樣品的電子結構以及軌域對稱性。我們的結果顯示，40nm與10nm的Sm0.67Sr0.33MnO3薄膜在z軸的方向上是受到壓縮的應力。我們更可以參照X光吸收能譜以及理論計算，發現當薄膜厚度越薄的樣品，Mn3+的貢獻是越多的，我們預測這是來自於基板與薄膜介面的介面層。另外，Sm0.67Sr0.33MnO3在低於磁性相變溫度下是具有鐵磁性金屬的性質。在本論文中，我們也運用磁圓偏振二向性吸收能譜去量測塊材與薄膜樣品的磁性，進而找出薄膜厚度與磁性的關係。

Sm1-xSrxMnO3 is a transition compound with a perovskite-type crystal structure. With different doping concentrations, Sm1-xSrxMnO3 exhibits various magnetic phase transitions and structural arrangement. Based on advanced epitaxial techniques, one can tailor the electronic structure of Sm0.67Sr0.33MnO3 which are epitaxially grown on a SrTiO3 (STO) substrate with different thickness. In this case, the strain from the substrates will influence the samples and distort the 3d orbital symmetry of manganese. Therefore, we not only conducted X-ray diffraction (XRD) experiment to confirm the crystal structure, but also the linear dichroism (LD) in soft X-ray absorption to investigate the electronic structure and orbital symmetry of the samples. Our results show that the z direction of 40-nm and 10-nm thin films are compressed. Furthermore, through X-ray absorption spectra and calculations, Mn3+ exists at the interface between substrates and thin films. The thinner the sample, the more Mn3+ contributes. In addition, Sm0.67Sr0.33MnO3 is ferromagnetic when the temperature is lower than the magnetic phase transition temperature. In this thesis, we used soft X-ray magnetic circular dichroism (XMCD) technique to compare difference between the bulk and the thin film samples and consequently found that the contribution of magnetism is thickness dependent.