Ferrimagnetism in EuFe4As12 revealed by Eu153 NMR and

Abstract

Filled skutterudite compound EuFe4As12 shows the highest magnetic ordering temperature of TC = 154 K among Eu-based skutterudite compounds, but its magnetic ground state has not been determined yet. Here, we performed 153 Eu nuclear magnetic resonance (NMR) and 75 As nuclear quadrupole resonance (NQR) measurements on EuFe4As12 to reveal its magnetic ground state as well as the physical properties from a microscopic point of view. From the temperature and magnetic field dependence of 153 Eu NMR spectrum in the magnetically ordered state, we found that the Eu ions are in Eu 2+ state with a nearly 7 µB corresponding to S = 7/2 spins. Combined with the magnetization measurements which show the reduced saturation moments of 4.5 µB/f.u., we determined the ground magnetic structure in EuFe4As12 to be ferrimagnetic where the Eu 2+ 4f and the Fe 3d ordered moments are ferromagnetically aligned in each sublattice but the moments between the sublattices are antiferromagnetically aligned. We also found the local distortion at the Eu site from the cubic symmetry in the magnetically ordered state. The relationship between the rattling motion of Eu atoms and the local symmetry of the Eu ions is discussed. From the 75 As NQR nuclear spin-lattice relaxation time measurements as well as 153 Eu NMR measurements, we found that the 4f electrons of the Eu ions are well described by the local moment picture in both the magnetic and paramagnetic metallic states.