X-ray $2p$ photoelectron and $L_{\alpha }$ resonant x-ray emission spectra of the $3d$ metals in ${\mathrm{Ni}}_2\mathrm{Mn}Z$ $(Z=\mathrm{In},\mathrm{Sn},\mathrm{Sb})$ Heusler alloys

Magnetic and chemical bonding effects in Heusler alloys ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{In}$, ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Sn}$, and ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Sb}$ were studied by soft x-ray spectroscopy. Exchange splitting detected in Mn $2p$ core-level x-ray photoelectron spectra and an increase of the Mn $L_{\beta }∕L_{\alpha }$ intensity ratio in nonresonant x-ray emission spectra show that atomic magnetic moment at Mn is higher than that of pure metal. Spin polarized density of states calculations and comparative analysis of Mn and Ni $L_{\alpha }$ resonant x-ray emission spectra (RXES) demonstrate that the spin splitting in Mn $3d$ shell is larger than in Ni $3d$ shell. The $d\text{−}d$ transitions observed in $L_{\alpha }$ RXES of Mn and Ni are suggested to be more intensive for Mn than for Ni valence electrons when initiated by off-resonant excitations. Experimental findings are supported by photoelectron spectra calculations and developed two-step model of resonant x-ray emission. The interplay between Mn $L_{\alpha }$ RXES and calculated magnetic moments of Mn atoms in alloys as a function of the type of $Z$ element is discussed.

Figure 1

Mn $3d$, Ni $3d$, and $Zp$ spin-resolved partial densities of states in ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{In}$, ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Sn}$, and ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Sb}$ as calculated by WIEN2K (Ref. 27).

Figure 2

Total density of states calculated using WIEN2K (Ref. 27).

Figure 3

Measured valence band photoelectron spectra of ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Z}$ alloys.

Figure 4

Mn $2p$ X-ray photoelectron spectra of Heusler alloys. The spectrum of pure manganese is given for reference. The $2p_{3∕2}$ core level binding energy of Mn in alloys is defined from the position of peak maxima which is labelled by a vertical dashed line.

Figure 5

Ni $2p$ XPS of Heusler alloys. The $2p_{3∕2}$ core level binding energy of Ni (dashed line) is the same as in metal. The example of the spectrum of metallic Nickel is available in Ref. 54.

Figure 6

Mn $L_{\alpha ,\beta }$ NXES. The vertical dotted line corresponds to the Mn $2p_{3∕2}$ core level binding energy taken from Fig. 4.

Figure 7

Ni $L_{\alpha ,\beta }$ NXES. The vertical dotted line corresponds to the Ni $2p_{3∕2}$ core level binding energy taken from Fig. 5.

Figure 8

Calculated Mn $2p$ x-ray photoelectron spectra of Heusler alloys.

Figure 9

Mn $L_{2,3}$ XAS (top frame) and $L_{\alpha }$ RXES of Heusler alloys and of elemental Mn (bottom frame) are shown at the left graph. The positions of the two excitation energies, one corresponding to the $L_3$ resonance (a) and off-$L_3$ resonance (b), are labeled by arrows in the corresponding XAS. The Mn $L_{\alpha }$ resonant x-ray emission spectra of alloys and elemental metal excited at the energies (a) and (b) are shown in the two separate panels labeled (a) and (b). The Mn $2p_{3∕2}$ core level binding energy taken from Fig. 4 is indicated by a vertical line. Each of Mn $L_{\alpha }$ RXES is assumed to consist from two peaks $A_R$ and $B_R$. Positions of these peaks in the photon energy scale are defined by the primary maxima in spectra. They are marked by dotted lines.

Figure 10

Ni $L_{2,3}$ XAS (top frame) and $L_{\alpha }$ RXES of Heusler alloys and of elemental Ni (bottom frame) are shown at the left graph. All designations are the same as in Fig. 9.

Figure 11

Mn $L_{\alpha ,\beta }$ Top frame: X-ray emission in the energy loss scale. Bottom frame: The Mn $3d$ DOS and its convolution with Gaussians to fit experimental resolution.

Figure 12

The experimental valence band spectrum Mn $L_{\alpha }$ and Ni $L_{\alpha }$ RXES and spin-polarized total DOS calculations in the binding energy scale. The Mn $L_{\alpha }$ and Ni $L_{\alpha }$ RXES were taken for the case of the off-$L_3$ resonant excitation (b) from Figs. 9, 10, respectively. The position of the Fermi energy at the ground state is defined by the $2p_{3∕2}$ binding energies taken from Figs. 4, 5. The spin-polarized total DOS is calculated by WIEN2K (Ref. 27).

Figure 13

Off-resonant x-ray emission spectra calculated for Mn $2p_{3∕2}$ core-level excitation from three different Heusler alloys. The excitation energy ${\omega }_0^{NR}$ corresponds to label (b) in Fig. 9.

Figure 14

Resonant x-ray emission spectra calculated for Mn $2p_{3∕2}$ core-level excitation from three different Heusler alloys. The excitation energy ${\omega }_0^R$ corresponds to label (a) in Fig. 9.