Anisotropy of Spin Fluctuations in a Tetragonal Heavy Fermion Antiferromagnet CeRhAl4Si2

An antiferromagnetic (AFM) Kondo lattice compound CeRhAl4Si2, which exhibits successive AFM transitions at TN1=14 K and TN2=9 K in zero external field, has been microscopically investigated by means of 27Al nuclear magnetic resonance (NMR) technique. In the high temperature range, magnetic excitations of 4f electrons can be well explained by isotropic localized spin fluctuations. Below ∼50 K, it begins to show a characteristic anisotropy of spin fluctuations, which suggests a competition between spin fluctuations and nesting instability in this system.