Low-energy spin dynamics in the antiferromagnetic phase of CaFe2As2

We present ⁷⁵As nuclear magnetic resonance data in the paramagnetic and magnetic states of single-crystal CaFe₂As₂. The electric field gradient and the internal magnetic field at the As sites change discontinuously below the first-order structural transition at T ₀=169 K. In the magnetic state, we find a single value of the internal hyperfine field consistent with commensurate antiferromagnetic order of Fe moments pointing in the ab plane. The spin lattice relaxation rate shows Korringa behavior for TlsimT ₀/3, reflecting the metallic nature of the ordered state. Surprisingly, T ₁^-1 exhibits a small peak at 10 K, revealing the presence of slow spin fluctuations that may be associated with domain wall motion.