Manikandan Dhamodaran, Boukhvalov D W, Amirthapandian S, Zhidkov I S, Kukharenko A I, Cholakh S O, Kurmaev E Z, Murugan Ramaswamy
Department of Physics, Pondicherry University, Puducherry 605 014, India.
Phys Chem Chem Phys. 2018 Feb 28;20(9):6500-6514. doi: 10.1039/c7cp07182e.
SnO and Mn-doped SnO single-phase tetragonal crystal structure quantum dots (QDs) of uniform size with control over dopant composition and microstructure were synthesized using the high pressure microwave synthesis technique. On a broader vision, we systematically investigated the influence of dilute Mn ions in SnO under the strong quantum confinement regime through various experimental techniques and density functional theoretical (DFT) calculations to disclose the physical mechanism governing the observed ferromagnetism. DFT calculations revealed that the formation of the stable (001) surface was much more energetically favorable than that of the (100) surface, and the formation energy of the oxygen vacancies in the stable (001) surface was comparatively higher in the undoped SnO QDs. X-ray photoelectron spectroscopy (XPS) and first-principles modeling of doped QDs revealed that the lower doping concentration of Mn favored the formation of MnO-like (Mn) structures in defect-rich areas and the higher doping concentration of Mn led to the formation of multiple configurations of Mn (Mn and Mn) in the stable surfaces of SnO QDs. Electronic absorption spectra indicated the characteristic spin allowed ligand field transitions of Mn and Mn and the red shift in the band gap. DFT calculations clearly indicated that only the substitutional dopant antiferromagnetic configurations were more energetically favorable. The gradual increase of magnetization at a low level of Mn-doping could be explained by the prevalence of antiferromagnetic manganese-vacancy pairs. Higher concentrations of Mn led to the appearance of ferromagnetic interactions between manganese and oxygen vacancies. The increase in the concentration of metallic dopants caused not just an increase in the total magnetic moment of the system but also changed the magnetic interactions between the magnetic moments on the metal ions and oxygen. The present study provides new insight into the fundamental understanding of the origin of ferromagnetism in transition metal-doped QDs.
采用高压微波合成技术合成了具有均匀尺寸、可控制掺杂成分和微观结构的SnO及Mn掺杂的SnO单相四方晶体结构量子点（QDs）。从更广泛的角度来看，我们通过各种实验技术和密度泛函理论（DFT）计算，系统地研究了在强量子限制 regime 下稀Mn离子在SnO中的影响，以揭示控制所观察到的铁磁性的物理机制。DFT计算表明，稳定（001）表面的形成在能量上比（100）表面更有利，并且在未掺杂的SnO量子点中，稳定（001）表面上氧空位的形成能相对较高。X射线光电子能谱（XPS）和掺杂量子点的第一性原理建模表明，较低的Mn掺杂浓度有利于在缺陷丰富区域形成MnO类（Mn）结构，而较高的Mn掺杂浓度导致在SnO量子点的稳定表面形成多种Mn构型（Mn和Mn）。电子吸收光谱表明了Mn和Mn的特征自旋允许配体场跃迁以及带隙中的红移。DFT计算清楚地表明，只有替代掺杂剂反铁磁构型在能量上更有利。在低水平Mn掺杂下磁化强度的逐渐增加可以用反铁磁锰 - 空位对的普遍存在来解释。较高浓度的Mn导致锰与氧空位之间出现铁磁相互作用。金属掺杂剂浓度的增加不仅导致系统总磁矩的增加，还改变了金属离子和氧上磁矩之间的磁相互作用。本研究为深入理解过渡金属掺杂量子点中铁磁性的起源提供了新的见解。
