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arXiv 1602.05804cond-mat.mtrl-sci
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在MgO(001)和Nb掺杂的SrTiO $_3$(001)上生长的外延NiO/Fe $_3$ O $_4$(001)异质结构的电子和磁性结构

Electronic and magnetic structure of epitaxial NiO/Fe$_3$O$_4$(001) heterostructures grown on MgO(001) and Nb-doped SrTiO$_3$(001)

K. Kuepper, O. Kuschel, N. Pathé, T. Schemme, J. Schmalhorst, A. Thomas, E. Arenholz M. Gorgoi, R. Ovsyannikov, S. Bartkowski, G. Reiss, J. Wollschläger

摘要:

我们研究了一些磁铁矿基薄膜的基本化学,电子和磁性。主要研究了MgO(001)和Nb-SrTiO $_3$(001)衬底上生长的NiO/Fe $_3$ O $_4$(001)双层薄膜。我们比较的结果与纯Fe $_3$ O $_4$(001)薄膜。结果发现,磁铁矿层被氧化,Fe $^{3+}$占主导地位的表面由于磁赤铁矿($γ$ -Fe $_2$ O $_3$)的形成,这减少了磁铁矿层的厚度。从约20 nm的层厚度上的阳离子分布接近于化学计量的Fe $_3$ O $_4$。在NiO和Fe $_3$ O $_4$之间的界面处,我们发现Ni处于二价态,在Ni 2 p核心水平X射线光电子能谱中具有NiO典型的明确的光谱特征。通过XMCD可以排除明显的NiFe $_2$ O $_4$中间层的形成。磁光克尔效应测量揭示了显着更高的矫顽场相比,MgO(001)和45 $^{\circ}$旋转磁易轴上生长的磁铁矿薄膜。我们讨论了磁性层的自旋磁矩,发现磁矩随薄膜厚度的增加而增加。在较低的厚度下,在Nb-SrTiO $_3$上生长的NiO/Fe $_3$ O $_4$薄膜的自旋磁矩显著降低。20 nm或更高的厚度导致自旋磁矩接近块状磁铁矿的自旋磁矩。

英文摘要:

We study the underlying chemical, electronic and magnetic properties of a number of magnetite based thin films. The main focus is placed onto NiO/Fe$_3$O$_4$(001) bilayers grown on MgO(001) and Nb-SrTiO$_3$(001) substrates. We compare the results with those obtained on pure Fe$_3$O$_4$(001) thin films. It is found that the magnetite layers are oxidized and Fe$^{3+}$ dominates at the surfaces due to maghemite ($γ$-Fe$_2$O$_3$) formation, which decreases with increasing magnetite layer thickness. From a layer thickness of around 20 nm on the cationic distribution is close to that of stoichiometric Fe$_3$O$_4$. At the interface between NiO and Fe$_3$O$_4$ we find the Ni to be in a divalent valence state, with unambiguous spectral features in the Ni 2p core level x-ray photoelectron spectra typical for NiO. The formation of a significant NiFe$_2$O$_4$ interlayer can be excluded by means of XMCD. Magneto optical Kerr effect measurements reveal significant higher coercive fields compared to magnetite thin films grown on MgO(001), and a 45$^{\circ}$ rotated magnetic easy axis. We discuss the spin magnetic moments of the magnetite layers and find that the moment increases with increasing thin film thickness. At low thickness the NiO/Fe$_3$O$_4$ films grown on Nb-SrTiO$_3$ exhibits a significantly decreased spin magnetic moments. A thickness of 20 nm or above leads to spin magnetic moments close to that of bulk magnetite.

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