Low energy spin dynamics in the antiferromagnetic phase of CaFe2As2

TL;DR

This study uses 75As NMR to investigate the low energy spin dynamics in CaFe2As2, revealing a first-order structural transition, commensurate antiferromagnetic order, metallic behavior, and slow spin fluctuations at low temperature.

Contribution

First detailed NMR analysis of spin dynamics in CaFe2As2 across the magnetic transition, highlighting slow spin fluctuations and their possible link to domain wall motion.

Findings

Discontinuous change in electric field gradient and internal magnetic field at T0=169 K.

Evidence of commensurate antiferromagnetic order with Fe moments in the ab plane.

Presence of slow spin fluctuations at low temperature, indicated by a peak in 1/T1.

Abstract

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 T0 = 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 T<T0/3, reflecting the metallic nature of the ordered state. Surprisingly, 1/T1 exhibits a small peak at 10 K, revealing the presence of slow spin fluctuations that may be associated with domain wall motion.