Anomalous Behavior of Itinerant Weak Ferromagnet LaFe4As12in NMR/NQR Studies

We report the results of As-nuclear quadrupole resonance (NQR) in LaFe 4 As 12 which shows itinerant ferromagnetic order at 5.2 K. We used high quality sample grown by high pressure synthesis. Appreciably broadened 75 As-NQR spectrum over the frequency range from 53.5 to 57.5 MHz observed below T C is the first microscopic evidence for a ferromagnetic order in LaFe 4 As 12 . In the paramagnetic state, Nowak et al. [Phys. Rev. B 79 (2009) 214411] reported that the nature of the low-energy spin excitations is explained by the SCR (self consistent renormalization) theory for weakly itinerant ferromagnetic metals from the results of NQR and NMR (nuclear magnetic resonance) measurements in the temperature range of 20–300 K. However, in the present As-NQR study, nuclear spin lattice relexation rate 1/ T 1 is anomalously enhanced below 100 K, suggesting the extra low-energy spin excitations other than the conventional SCR mechanism.