Electric-Field Control of the Orbital Occupancy and Magnetic Moment of a Transition-Metal Oxide

By using soft-x-ray linear and magnetic dichroism on ${\mathrm{La}}_{0.825}{\mathrm{Sr}}_{0.175}{\mathrm{MnO}}_3/{\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ ferromagnetic-ferroelectric heterostructures we demonstrate a nonvolatile modulation of the Mn $3d$ orbital anisotropy and magnetic moment. X-ray absorption spectroscopy at the Mn $L_{2,3}$ edges shows that the ferroelectric polarization direction modifies the carrier density, the spin moment, and the orbital splitting of $t_{2g}$ and $e_g$ Mn $3d$ states. These results are consistent with polar distortions of the oxygen octahedra surrounding the Mn ions induced by the switching of the ferroelectric polarization.

Figure 1

(a) (Left side) Top-view optical image of the FEFED clearly indicating the channel and Pad area of the Hall bar geometry. (Right side) Schematic view of the XAS experiment on the LSMO/PZT/LSMO FEFED. The photon linear polarizations can be set parallel ($p_{ab}$) or almost perpendicular to the $ab$ plane ($p_c$) and, the intensity of the related XAS spectra are labeled as $I_{ab}$ and $I_c$, respectively. CR and CL indicate photons circularly right and left polarized, respectively. (b) Ferroelectric switching of the PZT layer with positive voltage pulses $P$ and $U$, corresponding to the $\text{Pol}\uparrow$ state ($P$ pointing toward the top LSMO layer, see inset).

Figure 2

Mn $L_3$-edge isoXAS spectra measured at room temperature for both $\text{Pol}\downarrow$ (red line) and $\text{Pol}\uparrow$ (black line) states. The inset shows the complete energy dependence of the isoXAS spectra.

Figure 3

Comparison between the atomic multiplet calculations (solid blue lines) and the experimental XLD spectra described in the text for the $\text{Pol}\downarrow$ state. The dotted lines represent the integration curves calculated from the XLD spectrum and the related simulation. The inset in the upper panel sketches ${\pi }_{\text{orb}}$ as a function of the $P$ direction. In the lower panel the energy diagram is related to the ${\mathrm{XLD}}^{-}$ fitting parameters. The schematic ionic model, used to justify the modulation of the orbital occupancy has been re-adapted from Ref. [13]. XAS spectra were measured at 300 K in order to exclude any possible magnetic contribution.

Figure 4

Same as in Fig. 3 but related to the $\text{Pol}\uparrow$ state.