Antisite disorder in the battery material <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">LiFePO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:math>
J. Werner, Christoph Neef, Changhyun Koo, S. A. Zvyagin, Alexey Ponomaryov, R. Klingeler
Abstract
We report detailed magnetometry and high-frequency electron spin resonance (HF-ESR) measurements which allow detailed investigation on Li-Fe antisite disorder in single-crystalline $\mathrm{Li}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$, i.e., exchange of ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Li}}^{+}$ ions. The data imply that magnetic moments of ${\mathrm{Fe}}^{2+}$ ions at Li positions do not participate in long-range antiferromagnetic order in $\mathrm{Li}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$ but form quasifree moments. Anisotropy axes of the magnetic moments at antisite defects are attached to the main crystallographic directions. The local character of these moments is confirmed by associated linear resonance branches detected by HF-ESR studies. Magnetic anisotropy shows up in significant zero-field splittings of $\mathrm{\ensuremath{\Delta}}=220(3)$ GHz, ${\mathrm{\ensuremath{\Delta}}}^{\ensuremath{'}}\ensuremath{\sim}50$ GHz, and a highly anisotropic $g$ factor, i.e., ${g}_{a}=1.4, {g}_{b}=2.0$, and ${g}_{c}=6.3$. We demonstrate a general method to precisely determine Fe-antisite disorder in $\mathrm{Li}\mathrm{Fe}\mathrm{P}{\mathrm{O}}_{4}$ from magnetic studies which implies a density of paramagnetic ${\mathrm{Fe}}^{2+}$ ions at Li positions of 0.53%.