Insights into <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>ε</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mi>Fe</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:math> interactions via Cr doping

Innovative materials, particularly multiferroics, have the potential to transform technology. Full optimization of their usage will require an in-depth understanding of the underlying electronic and magnetic interactions. One such material is $\ensuremath{\epsilon}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$. However, because this hard ferrimagnet with strong magnetoelectric coupling is composed of only ${\mathrm{Fe}}^{3+}$, distinguishing the role of the various sites is incredibly challenging. To overcome this challenge, ${\mathrm{Cr}}^{3+}$ ions were doped into the ${\mathrm{DO}}_{h1}$ sites of $\ensuremath{\epsilon}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ nanoparticles, effectively creating electron deficient defects. The $\ensuremath{\epsilon}$-(${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{)}_{2}{\mathrm{O}}_{3}$ ($x=0.01$ to 0.12) nanoparticles have reduced ${\ensuremath{\mu}}_{0}{H}_{C}(T)$ and ${M}_{S}(T)$ as the Cr concentration increases. The impact of Cr doping on the local electronic and magnetic structure is characterized. At 10 K, subtle changes are measured, with the ${\mathrm{T}}_{d}$ site electrons becoming increasingly localized as the concentration of electron-deficient ${\mathrm{DO}}_{h1}$ sites increases. Far more dramatic changes occur at 300 K, when the ${\mathrm{T}}_{d}$ site of the $\ensuremath{\epsilon}$-(${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{)}_{2}{\mathrm{O}}_{3}$ splits into two distinct local environments with ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{4+}$ character. The nature of this splitting suggests that dynamic electron interactions play a significant role in $\ensuremath{\epsilon}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$'s magnetic anisotropy and magnetoelectric properties.

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