Photoemission and x-ray absorption studies of the isostructural to Fe-based superconductors diluted magnetic semiconductor ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\left({\mathrm{Zn}}_{1-y}{\mathrm{Mn}}_y\right){}_2{\mathrm{As}}_2$

The electronic and magnetic properties of a new diluted magnetic semiconductor (DMS) ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\left({\mathrm{Zn}}_{1-y}{\mathrm{Mn}}_y\right){}_2{\mathrm{As}}_2$, which is isostructural to so-called 122-type Fe-based superconductors, are investigated by x-ray absorption spectroscopy (XAS) and resonance photoemission spectroscopy (RPES). Mn $L_{2,3}$-edge XAS indicates that the doped Mn atoms have a valence 2+ and strongly hybridize with the $4p$ orbitals of the tetrahedrally coordinating As ligands. The Mn $3d$ partial density of states obtained by RPES shows a peak around 4 eV and is relatively high between 0 and 2 eV below the Fermi level ($E_F$) with little contribution at $E_F$, similar to that of the archetypal DMS ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$. This energy level creates a $d^5$ electron configuration with $S=5/2$ local magnetic moments at the Mn atoms. Hole carriers induced by K substitution for Ba atoms go into the top of the As $4p$ valence band and are weakly bound to the Mn local spins. The ferromagnetic correlation between the local spins mediated by the hole carriers induces ferromagnetism in ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x\left({\mathrm{Zn}}_{1-y}{\mathrm{Mn}}_y\right){}_2{\mathrm{As}}_2$.

Figure 1

Band structures and the density of states for ${\mathrm{BaZn}}_2{\mathrm{As}}_2$ calculated using the modified Becke-Johnson exchange potential. The lattice parameters $a=4.120$ Å, $c=13.578$ Å [7], and $h_{\text{As}}=1.541$ Å [15] are used in the calculation.

Figure 2

Mn $L_{2,3}$-edge XAS spectra of ${\mathrm{Ba}}_{0.7}{\mathrm{K}}_{0.3}\left({\mathrm{Zn}}_{0.85}{\mathrm{Mn}}_{0.15}\right){}_2{\mathrm{As}}_2$ (Mn-${\mathrm{BaZn}}_2{\mathrm{As}}_2$). The spectrum is compared with those of ${\mathrm{Ga}}_{0.922}{\mathrm{Mn}}_{0.078}\mathrm{As}$ [22], ${\mathrm{Ga}}_{0.958}{\mathrm{Mn}}_{0.042}\mathrm{N}$ [23], Mn metal [24], $\mathrm{Ba}({\mathrm{Fe}}_{0.92}{\mathrm{Mn}}_{0.08}){}_2{\mathrm{As}}_2$ [25], ${\mathrm{LaMnO}}_3$, and MnO [26]. The valence and the local symmetry of the Mn atom are indicated for each compound.

Figure 3

(a) Evolution of the valence-band photoemission spectra of Mn-${\mathrm{BaZn}}_2{\mathrm{As}}_2$ with photon energies $h\nu =635$–643 eV. Excitation photon energies are shown by the arrows on the XAS spectrum in (b).

Figure 4

(a) Evolution of the valence-band photoemission difference spectra of Mn-${\mathrm{BaZn}}_2{\mathrm{As}}_2$ for photon energies $h\nu =635$–643 eV. The off-resonance photoemission spectrum at the bottom of the panel ($h\nu =635$ eV) has been subtracted from the original spectra in order to highlight the resonant enhancement of the spectral weight. On-resonance spectrum is shown by a black curve. Vertical bars indicate a constant kinetic energy characteristic of Auger-electron emission if it existed. The absence of clear Auger peaks reflects the localized nature of the Mn $3d$ electrons. (b) Mn $3d$ partial density of states deduced by subtracting the off-resonance spectrum ($h\nu =635$ eV) from the on-resonance spectra ($h\nu =638.5$ eV). (f) Mn $3d$ PDOS of ${\mathrm{Ga}}_{0.957}{\mathrm{Mn}}_{0.043}\mathrm{As}$ [31] compared with that of Mn-${\mathrm{BaZn}}_2{\mathrm{As}}_2$.