Abstract
We have investigated the role of $\mathrm{M}{\mathrm{n}}^{3+}$ Jahn-Teller distortion in driving ferromagnetism in the $\mathrm{LaM}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{S}{\mathrm{c}}_{x}{\mathrm{O}}_{3}$ series. The replacement of Mn by Sc in $\mathrm{LaMn}{\mathrm{O}}_{3}$ decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the $\mathrm{LaSc}{\mathrm{O}}_{3}$ sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in $\mathrm{LaMn}{\mathrm{O}}_{3}$ into a nearly regular one in $\mathrm{LaSc}{\mathrm{O}}_{3}$. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc $K$ edges reveal the stability of both Jahn-Teller distorted $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedron and nearly regular $\mathrm{Sc}{\mathrm{O}}_{6}$ octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra spatially ordered as in $\mathrm{LaMn}{\mathrm{O}}_{3}$ and nearly regular $\mathrm{Sc}{\mathrm{O}}_{6}$ octahedra. This result contrasts with the pseudocubic phase and the appearance of regular $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra in $\mathrm{LaM}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{G}{\mathrm{a}}_{x}{\mathrm{O}}_{3}$ for $xg0.5$. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the $\mathrm{M}{\mathrm{n}}^{3+}$ atom is allocated. Besides, a ferromagnetic ground state is observed for $xg0.5$ in both series independently of the presence (or not) of Jahn-Teller distortions around $\mathrm{M}{\mathrm{n}}^{3+}$, which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in $\mathrm{LaM}{\mathrm{n}}_{1\text{\ensuremath{-}}x}{B}_{x}{\mathrm{O}}_{3}$ $(B=\text{Sc or Ga})$.
Highlights
The exotic properties of RMnO3 (R = rare earth) perovskites are being extensively exploited for the manufacturing of thin films or artificial heterostructures for technological applications [1]
In order to clarify the role of the JT distortion in the emergence of ferromagnetism in isovalent Mn-site substituted LaMnO3, we have studied the crystallographic structure by x-ray powder diffraction (XRD) and the local structure at the Mn and Sc sites by x-ray absorption spectroscopy (XAS) of LaMn1-xScxO3 compounds
The lattice parameters refined for the LaMnO3 sample are in agreement with the results obtained in Ref. [20], confirming the right oxygen stoichiometry
Summary
Scandium transforms from the (3x2 − r2)/(3y2 − r2) states into the 3z2 − r2 state (spin-flipping model) Both models assume that the change from A-type AFM to FM ordering is originated by the orbital direction adopted by the Mn3+ ion and it is similar for Ga and Sc nonmagnetic substitutions, so the atomic eg orbital would be perturbed in the same way for the two series. This explanation contrasts with the experimental determination of the local geometrical structure of the Mn atom by x-ray absorption spectroscopy (XAS) for LaMn1-xGaxO3. This study reveals the similarities and differences with the Ga-substituted series and allows us to determine the role of the Mn-sublattice dilution over the local structural distortions in driving ferromagnetism after Ga/Sc substitution
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