Electronic structures of ${\mathrm{Fe}}_{3-x}{M}_x{\mathrm{O}}_4$ $(M=\mathrm{Mn},\mathrm{Zn})$ spinel oxide thin films investigated by x-ray photoemission spectroscopy and x-ray magnetic circular dichroism

We fabricated ${\mathrm{Fe}}_{3-x}{M}_x{\mathrm{O}}_4$ $(M=\mathrm{Mn},\mathrm{Zn})$ thin film by pulsed laser deposition technique and investigated their electronic structure by hard x-ray photoemission spectroscopy (HX-PES) and x-ray magnetic circular dichroism (XMCD). HX-PES and XMCD revealed that the solid solution system of ${\mathrm{Fe}}_{3-x}{M}_x{\mathrm{O}}_4$ $(M=\mathrm{Mn},\mathrm{Zn})$ is the best candidate for tunable ferromagnetic oxide semiconductor judging from systematic change of Fe, Mn core-level spectra, and valence band spectra by substitution. We present a model to explain modulation of electric and magnetic properties and electronic structure evolution caused by strongly correlated electron.

Figure 1

(Color online) (a) Carrier concentration and carrier mobility of ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x{\mathrm{O}}_4$ thin films ($x=0$, 0.1, 0.5, and 0.8) and ${\mathrm{Fe}}_{3-x}{\mathrm{Zn}}_x{\mathrm{O}}_4$ thin films ($x=0$ and 0.5) with a substitution ratio estimated from an ordinary Hall resistance term $(d{R}_{\text{Hall}}∕dH$ at high magnetic field) (Refs. 10, 11). (b) Schematic illustration of the carrier control mechanism in ${\mathrm{Fe}}_{3-x}{M}_x{\mathrm{O}}_4$ $(M=\mathrm{Mn},\mathrm{Zn})$.

Figure 2

(Color online) (a) $\mathrm{Mn}2p$ core-level HX-PES spectra of ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x{\mathrm{O}}_4$ thin films (0.1 and 0.5) taken at $h\nu =7.94\mathrm{keV}$. (b) $\mathrm{Mn}2p$ core absorption spectrum of ${\mathrm{Fe}}_{2.5}{\mathrm{Mn}}_{0.5}{\mathrm{O}}_4$ thin film under a magnetic field of $3\mathrm{T}$ at $150\mathrm{K}$. (c) $\mathrm{Fe}2p$ core-level HX-PES spectra of ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x{\mathrm{O}}_4$ thin films (0, 0.1, and 0.5).

Figure 3

(Color online) (a) Mn substitution ratio $\left(x\right)$ dependence of x-ray magnetic circular dichroism (XMCD) spectra for $\left({\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x\right){\mathrm{O}}_4$ thin films ($x=0$, 0.1, and 0.5) obtained from the intensity difference between core absorption spectra taken at opposite helicity. (b) The magnified figure in dashed area. The peak energy position for each Fe ion was obtained from Ref. 20 (c) Mn substitution ratio $\left(x\right)$ dependence of XMCD spectra for ${\left({\mathrm{Fe}}^{2+}\right)}_{\mathrm{B}}$, ${\left({\mathrm{Fe}}^{3+}\right)}_{\mathrm{B}}$, and ${\left({\mathrm{Fe}}^{2+}\right)}_{\mathrm{A}}$ normalized by that for $x=0$ component.

Figure 4

(Color online) $\mathrm{Fe}2p$ core-level HX-PES spectra of ${\mathrm{Fe}}_{3-x}{\mathrm{Zn}}_x{\mathrm{O}}_4$ thin films (0, 0.5, and 0.9) taken at $h\nu =7.94\mathrm{keV}$.

Figure 5

(Color online) Valence band HX-PES spectra of ${\mathrm{Fe}}_{2.5}{\mathrm{Mn}}_{0.5}{\mathrm{O}}_4$ thin film, ${\mathrm{Fe}}_{3-x}{\mathrm{Zn}}_x{\mathrm{O}}_4$ thin films (0, 0.5, and 0.9), and bulk $\mathrm{Zn}{\mathrm{Fe}}_2{\mathrm{O}}_4$ taken at $h\nu =7.94\mathrm{keV}$.

Figure 6

(Color online) Schematic illustration of electronic structure evolution by $M^{2+}$ substitution. (a) Rigid band model. (b) Mott-Hubbard model. Only $\mathrm{O}2p$ and $\mathrm{Fe}3d$ at the B site are shown for simplicity. DOS of Fe and ${\mathrm{M}}^{2+}$ ions at the A site were omitted. (c) Dependence of $0.5\mathrm{eV}$ peak position on Mn and Zn substitutions for ${\mathrm{Fe}}_{3-x}{\mathrm{Mn}}_x{\mathrm{O}}_4$ thin films ($x=0$ and 0.5) and ${\mathrm{Fe}}_{3-x}{\mathrm{Zn}}_x{\mathrm{O}}_4$ thin films ($x=0$, 0.5, and 0.9).