Abstract
Spinel-type CoFe2O4 is a ferrimagnetic insulator with the Néel temperature exceeding 790 K, and it shows strong cubic magnetocrystalline anisotropy (MCA) in bulk materials. However, when a CoFe2O4 film is grown on other materials, its magnetic properties are degraded so that so-called magnetically dead layers are expected to be formed in the interfacial region. We investigate how the magnetic anisotropy of CoFe2O4 is modified at the interface of CoFe2O4/Al2O3 bilayers grown on Si(111) using x-ray magnetic circular dichroism. We find that the thinner CoFe2O4 films have significantly smaller MCA values than bulk materials. The reduction in MCA is explained by the reduced number of Co2+ ions at the Oh site, as reported by a previous study [Wakabayashi et al., Phys. Rev. B 96, 104410 (2017)].
Highlights
Spinel-type cobalt ferrite (CoFe2O4) is a classical ferrimagnetic insulator with the Néel temperature exceeding 790 K and exhibits strong cubic magnetocrystalline anisotropy (MCA)
Magnetic field-angle-dependent x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements were performed at room temperature using a superconducting vector-magnet XMCD apparatus16 installed at the undulator beamline BL-16A of the Photon Factory, High Energy Accelerator Research Organization (KEK-PF)
Since the XMCD intensity is proportional to the magnetic moment projected onto the x-ray incident direction [Mproj = M cos(θM − 45○)], its dependence reflects the change in the magnetization direction θM under varying
Summary
Spinel-type cobalt ferrite (CoFe2O4) is a classical ferrimagnetic insulator with the Néel temperature exceeding 790 K and exhibits strong cubic magnetocrystalline anisotropy (MCA). Heterostructures incorporating thin (CoFe2O4) layers have attracted much attention as spintronics devices because of the spin-dependent bandgap and high Néel temperature of (CoFe2O4).. A (CoFe2O4)based tunnel barrier acts as a spin filter because electrons have spin-dependent tunneling probabilities.. The experimentally obtained spin-filtering efficiency of (CoFe2O4)-based tunnel barriers still remains lower than theoretical values of 100%.2,6,7. As a possible cause of the low spin-filtering efficiency, it has been proposed that structural and/or chemical disorder leads to the scitation.org/journal/adv formation of impurity states in the spin-dependent gap.. In order to improve the spin filtering efficiency, it is essential to understand the electronic and magnetic phenomena at the interfaces Cubic MCA has been successfully explained by the single-ion anisotropy of Co2+ ions at inequivalent Oh sites. Recently, heterostructures incorporating thin (CoFe2O4) layers have attracted much attention as spintronics devices because of the spin-dependent bandgap and high Néel temperature of (CoFe2O4). For example, a (CoFe2O4)based tunnel barrier acts as a spin filter because electrons have spin-dependent tunneling probabilities. the experimentally obtained spin-filtering efficiency of (CoFe2O4)-based tunnel barriers still remains lower than theoretical values of 100%.2,6,7 As a possible cause of the low spin-filtering efficiency, it has been proposed that structural and/or chemical disorder leads to the scitation.org/journal/adv formation of impurity states in the spin-dependent gap. In order to improve the spin filtering efficiency, it is essential to understand the electronic and magnetic phenomena at the interfaces
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