X-ray spectroscopic study ofBaFeO3thin films: AnFe4+ferromagnetic insulator

Abstract

We investigated the electronic and magnetic properties of fully oxidized BaFeO3 thin films, which show ferromagnetic-insulating properties with cubic crystal structure, by hard x-ray photoemission spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). We analyzed the results with configuration-interaction (CI) cluster-model calculations for Fe 4+ , which showed good agreement with the experimental results. We also studied SrFeO3 thin films, which have an Fe 4+ ion helical magnetism in cubic crystal structure, but are metallic at all temperatures. We found that BaFeO3 thin films are insulating with large magnetization (1.7µB /formula unit) under ∼ 1 T, using valence-band HAXPES and Fe 2p XMCD, which is consistent with the previously reported resistivity and magnetization measurements. Although Fe 2p core-level HAXPES and Fe 2p XAS spectra of BaFeO3 and SrFeO3 thin films are quite similar, we compared the insulating BaFeO3 to metallic SrFeO3 thin films with valence-band HAXPES. The CI cluster-model analysis indicates that the ground state of BaFeO3 is dominated by d 5 L (L: ligand hole) configuration due to the negative charge transfer energy, and that the band gap has significant O 2p character. We revealed that the differences of the electronic and magnetic properties between BaFeO3 and SrFeO3 arise from the differences in their lattice constants, through affecting the strength of hybridization and bandwidth.

Itinerancy-dependent noncollinear spin textures in SrFeO3, CaFeO3 , and CaFeO3/SrFeO3Rogge1, Green2, Sutarto3 et al. 2019Phys. Rev. Materials285150View full textAdd to dashboardCite

“…As seen in Fig. 4, off the Bragg condition the measured intensity has features that resemble an x-ray absorption spectrum of these ferrates, as expected, where the strong prepeak feature between 527.0-529.5 eV arises from the oxygen ligand holes due to the negative charge transfer energy [31,40,41]. At the Bragg condition, there is a clear enhancement of the intensity within the prepeak region only.…”

Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic InsulatingBaFeO3Thin Films

“…3, we show the amplitude of the reflectivity change, which is a measure of the spectral weight transfer indicative of the insulator-to-metal transition, as a function of laser fluence. From the clear threshold behavior of this quantity we deduce that a sufficiently high density of excited carriers reduces electron-electron and electron-phonon interactions, which are the origins of the insulating properties in BaFeO 3 thin films [16,17].…”

“…After the deposition, BaFeO 2.5 thin films were annealed at 200 • C under ozone atmosphere to obtain BaFeO 3 thin films [16]. The quality of the thin-film samples were confirmed by xray diffraction, Fe 2p x-ray absorption spectroscopy, and Fe 2p core-level hard x-ray photoemission spectroscopy measurements by comparing cluster-model calculations, which found that the formal valence of Fe was 4+ [16,17]. The experimental geometry is shown schematically in Fig.…”

“…Figure 1 (c) shows the photon-energy dependence of reflectivity and MCDR. Although the photon-energy dependence of MCDR is different from the circular dichroism obtained from x-ray absorption spectra [17], it is a suited measure of the sample magnetization [19]. We fixed the photon energy to be hν = 714 eV, and the time evolution of the intensities of reflectivity as well as XMCD at this photon energy are traced in order to investigate the electronic and magnetic dynamics of BaFeO 3 thin films.…”

“…The large magnetic moment of BaFeO 3 thin films results in quite large peak intensity of Fe 2p x-ray magnetic circular dichroism (XMCD), ∼ 18 % of the x-ray absorption peak * Electronic address: wadati@issp.u-tokyo.ac.jp; URL: http://www.geocities.jp/qxbqd097/index2.htm intensity [17]. Thus, BaFeO 3 thin films are appropriate samples to carry out time-resolved magnetic circular dichroism experiments.…”