Optical and magneto-optical study of nickel and cobalt ferrite epitaxial thin films and submicron structures
Optical and magneto-optical study of nickel and cobalt ferrite epitaxial thin films and submicron structures
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DOI：
10.1063/1.4792749
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发表时间：
2013-02-28
影响因子：
3.2
通讯作者：
Kortus, Jens
中科院分区：
文献类型：
--
作者：
Himcinschi, Cameliu;Vrejoiu, Ionela;Kortus, Jens
采用脉冲激光沉积技术在掺Nb的钛酸锶衬底上制备了镍、钴铁氧体的外延薄膜和有序亚微米结构阵列。X射线衍射和原子力显微镜分析表明，所制备的薄膜结晶质量好，表面光滑。在铁氧体薄膜的偏振相关拉曼光谱中观察到了比立方尖晶石结构更多的声子带。这是由于八面体位置上Ni2+(或Co2+)和Fe3+离子的短程有序化导致对称性降低。在亚微米结构的拉曼光谱中也观察到了相同的行为，表明阳离子的分布与薄膜中的相同。在0.73-5 eV的光子能量范围内，用椭偏法测定了镍和钴铁氧体的介电函数的对角分量。用带隙模型分析了吸收边，计算了间接和直接光学跃迁的能量。结果表明，镍和钴铁氧体均为间接带隙材料，禁带宽度分别为1.65 eV和1.42 eV，而第一直接跃迁分别为2.69 eV和1.95 eV。磁光克尔效应光谱与椭圆偏振光谱相结合，可以在1.7 eV到5 eV的能量范围内测定介电张量的非对角元。(C)2013年美国物理研究所。[http://dx.doi.org/10.1063/1.4792749]
Epitaxial films and ordered arrays of submicron structures of nickel and cobalt ferrites were deposited on Nb doped SrTiO3 by pulsed laser deposition. X-Ray diffraction and atomic force microscopy showed that the films have a good crystalline quality and smooth surfaces. A larger number of phonon bands was observed in the polarization dependent Raman spectra of the ferrite films than expected for the cubic spinel structures. This is explained by short range ordering of the Ni2+ (or Co2+) and Fe3+ cations at the octahedral sites inducing a lowering of the symmetry. The same behavior was also observed in the Raman spectra measured for the submicron structures, suggesting the same cation distribution as in the films. The diagonal components of the dielectric function for nickel and cobalt ferrites are determined from ellipsometry in the 0.73-5 eV photon energy range. The absorption edge was analyzed using a bandgap model and the energies for the indirect and direct optical transitions were calculated. It was found that both nickel and cobalt ferrites are indirect bandgap materials with bandgaps of 1.65 eV and 1.42 eV, respectively, while the first direct transitions lie at 2.69 eV and 1.95 eV, respectively. Magneto-optical Kerr effect spectroscopy in combination with spectroscopic ellipsometry allowed the off-diagonal elements of the dielectric tensor to be determined in the energy range from 1.7 eV to 5 eV. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792749]