2017/04/06 by Yuki K. Wakabayashi, Yosuke Nonaka, Yukiharu Takeda +13 · 47 citations
Chemistry · Materials Science · Physics and Astronomy · #Absorption spectroscopy #Chemistry #Cluster (spacecraft) #Computer science #Condensed matter physics #Crystallography #Ferrimagnetism #Ferromagnetism #Magnetic Properties and Synthesis of Ferrites #Magnetic circular dichroism #Magnetic field #Magnetic properties of thin films #Magnetization #Materials science #Optics #Physics #Spectral line #Superexchange #X-ray absorption spectroscopy #ZnO doping and properties #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.96.104410
published in Physical review. B./Physical review. B 96(10) (American Physical Society)
arxiv created 2017/04/06 · openalex created_date 2017/04/28 · openalex publication_date 2017/09/11 · arxiv updated 2017/09/20 · openalex updated_date 2026/08/05
Epitaxial CoFe2O4/Al2O3 bilayers are expected to be highly efficient spin injectors into Si owing to the spin filter effect of CoFe2O4. To exploit the full potential of this system, understanding the microscopic origin of magnetically dead layers at the CoFe2O4/Al2O3 interface is necessary. In this paper, we study the cation distribution, electronic structures, and the magnetic properties of CoFe2O4(111) layers with various thicknesses (thickness d=1.4, 2.3, 4, and 11 nm) in the epitaxial CoFe2O4(111)/Al2O3(111)/Si(111) structures using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) combined with cluster-model calculation. The magnetization of CoFe2O4 measured by XMCD gradually decreases with decreasing thickness d, and finally, a magnetically dead layer is clearly detected at d=1.4\phantom\rule0.16em0exnm. The magnetically dead layer has frustration of magnetic interactions, which is revealed from comparison between the magnetizations at 300 and 6 K. From analysis using configuration-interaction cluster-model calculation, the decrease of d leads to a decrease in the inverse-to-normal spinel structure ratio and also a decrease in the average valence of Fe at the octahedral sites. These results strongly indicate that the magnetically dead layer at the CoFe2O4/Al2O3 interface originates from various complex networks of superexchange interactions through the change in the cation distribution and electronic structure. Furthermore, from comparison of the magnetic properties between d=1.4 and 2.3 nm, it is found that the ferrimagnetic order of the magnetically dead layer at the CoFe2O4/Al2O3 interface is partially restored by increasing the thickness from d=1.4 to 2.3 nm.