Combining geometrical frustration and one-dimensional magnetism boosts quantum fluctuations and leads to unusual states of quantum matter. We report the magnetic behavior of a well-separated $S=\frac{5}{2}$ sawtooth spin chain compound ${\mathrm{CaFe}}_2\mathrm{O}{\left({\mathrm{PO}}_4\right)}_2$ (CFPO). Magnetic susceptibility, heat capacity, and ${}^{31}\mathrm{P}$ nuclear magnetic resonance measurements show evidence of strong magnetic frustration in the compound. Despite a relatively large antiferromagnetic Curie-Weiss temperature of about $-1073\mathrm{K}$, the compound exhibits multiple magnetic transitions at low temperatures at 15.5, 10.4, and 7.8 K, respectively, with a frustration parameter $\left(\mathit{f}\approx |{\theta }_{\text{CW}}|/T_{\text{N}}\right)$ about 70. The Knight shift shows a broad maximum around 70 K for P1 and P2 sites. The spin-lattice relaxation rate $1/T_1$ follows temperature-independent behavior well above the long-range order (LRO). First-principles calculations capture the strong antiferromagnetic interactions in this quasi-one-dimensional sawtooth lattice, providing a microscopic explanation for the experimentally observed frustration, low dimensionality, and the onset of LRO at low temperatures. Our results indicate that CFPO exhibits the presence of short-range correlations and persistent spin dynamics characteristics above the LRO, which probably stem from the $S=\frac{5}{2}$ sawtooth spin chain model.

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• Magnetic susceptibility
• 1-dimensional spin chains
• Antiferromagnets
• Density functional calculations
• Nuclear magnetic resonance