Induced noncollinear magnetic order of ${\mathrm{Nd}}^{3+}$ in $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_3$ observed by resonant soft x-ray diffraction

Soft x-ray resonant magnetic diffraction at the Nd $M$ edges was performed on a $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_3$ epitaxial film to investigate the magnetic ordering of the Nd ions below the metal-insulator transition. A noncollinear magnetic structure induced by the Ni magnetic moments best describes the azimuthal angle dependency of the $(1∕2,0,1\mathrm{∕}2)$ reflection. This confirms the Ni spin structure observed with soft x-ray diffraction experiments performed at the Ni $L$ edge, providing further evidence of charge disproportionation without orbital order below the metal-insulator transition in $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_3$.

Figure 1

(Color online) Resonant soft x-ray diffraction geometry at the RESOXS end station. The polarization of the incident x rays is either $\sigma$ or $\pi$. $\widehat{u}$ indicates the experimental coordinate system and $\psi$ the azimuthal angle. $\mathbf{k}$ and ${\mathbf{k}}^{\prime }$ are the wave vectors of the incident and diffracted x rays respectively, and $\tau$ is the scattering vector.

Figure 2

(a) Fluorescence at the Nd $M$ edges, recorded with the CCD camera. (b) Intensity of the $(1∕2,0,1∕2)$ reflection recorded with the CCD camera, at the Nd $M$ edges at $T=40\mathrm{K}$ and $\psi =0°$ for $\pi$ (filled circles) and $\sigma$ (open circles) incident radiation. A spectrum recorded at $250\mathrm{K}$ with $\sigma$ incident radiation (continuous line) is also shown.

Figure 3

Temperature dependence of the $(1∕2,0,1∕2)$ diffracted intensity at the Nd $M_4$ edge (filled circles) compared to that recorded at Ni $L_3$ edge (open circles) (Ref. 11). The dotted line corresponds to the calculated intensity originating from the Nd magnetic moments that are induced by the Ni magnetic order, as explained in the text.

Figure 4

Azimuthal angle dependence of the $(1∕2,0,1∕2)$ reflection at the Nd $M_4$ edge recorded at $T=35\mathrm{K}$ compared to the azimuthal angle dependence recorded at the Ni $L$ edge. The solid and dotted lines correspond to the noncollinear and up-up-down-down magnetic structures, respectively.

Figure 5

(Color online) Two magnetic structures that have been proposed for $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_3$: (a) The noncollinear magnetic structure (Ref. 11); (b) the up-up-down-down magnetic structure (Ref. 2). Nd and Ni ions are indicated by large (black) and small (red or blue) spheres, respectively. Magnetic moment directions are indicated with arrows.