d 轨道介导的束缚磁极化子在铁磁 Ce 掺杂 BaTiO3 纳米颗粒中的存在及其丰富的双光子吸收截面。

d orbital-mediated bound magnetic polarons in ferromagnetic Ce-doped BaTiO nanoparticles and their enriched two-photon absorption cross-section.

机构信息

Nonlinear Optical Materials Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu, India.

出版信息

Phys Chem Chem Phys. 2019 Feb 13;21(7):4032-4045. doi: 10.1039/c8cp06055j.

DOI:10.1039/c8cp06055j

PMID:30720029

Abstract

The enriched ferromagnetism and two-photon absorption (TPA) cross-section of perovskite BaTiO3 nanoparticles are indispensable for magnetic and optical data storage applications. In this work, hydrothermally synthesized Ce-doped BaTiO3 nanoparticles exhibited the maximum room temperature ferromagnetism (4.26 × 10-3 emu g-1) at 4 mol% due to the increase in oxygen vacancies, as evidenced by X-ray photoelectron and electron spin resonance spectroscopy and density functional theory (DFT) calculations. Hence, the oxygen vacancy-constituted bound magnetic polaron (BMP) model was invoked to explain the enhancement in ferromagnetism. The BMP theoretical model indicated an increase in BMP magnetization (M0, 3.0 to 4.8 × 10-3 emu g-1) and true spontaneous moment per BMP (meff, 4 to 9.88 × 10-4 emu) upon Ce doping. DFT calculations showed that BMPs mediate via the Ti dz2 orbitals, leading to ferromagnetism. Besides, it is known that the magnetic moment induced by Ce at the Ba site is higher than Ce at the Ti site in the presence of oxygen vacancies. The open aperture Z-scan technique displayed the highest TPA coefficient, β (7.08 × 10-10 m W-1), and TPA cross-section, σTPA (455 × 104 GM), at 4 mol% of Ce as a result of the robust TPA-induced excited state absorption. The large σTPA is attributed to the longer excited state lifetime, τ (7.63 ns), of the charge carriers created by oxygen vacancies and Ce ions, which encounter several electronic transitions in the excited sub-states.

摘要

钙钛矿 BaTiO3 纳米粒子的丰富铁磁性和双光子吸收（TPA）截面对于磁光数据存储应用是不可或缺的。在这项工作中，水热合成的 Ce 掺杂 BaTiO3 纳米粒子在 4 mol%时表现出最大的室温铁磁性（4.26×10-3 emu g-1），这是由于氧空位的增加，这一点可以通过 X 射线光电子能谱和电子自旋共振谱以及密度泛函理论（DFT）计算得到证实。因此，引入了氧空位构成的束缚磁极化子（BMP）模型来解释铁磁性的增强。BMP 理论模型表明，Ce 掺杂后 BMP 磁化强度（M0，从 3.0 增加到 4.8×10-3 emu g-1）和每个 BMP 的真实自发矩（meff，从 4 增加到 9.88×10-4 emu）都有所增加。DFT 计算表明，BMP 通过 Ti dz2 轨道介导，导致铁磁性。此外，在存在氧空位的情况下，Ce 在 Ba 位诱导的磁矩高于 Ce 在 Ti 位的磁矩。开孔径 Z 扫描技术显示，在 4 mol% Ce 掺杂时，TPA 系数β（7.08×10-10 m W-1）和 TPA 截面σTPA（455×104 GM）最高，这是由于强 TPA 诱导的激发态吸收。大的 σTPA 归因于氧空位和 Ce 离子产生的载流子的更长激发态寿命 τ（7.63 ns），它们在激发亚态中经历了几次电子跃迁。