Nuclear magnetic resonance investigation of the heavy fermion system Ce2CoAl7Ge4

We present nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements performed on single crystalline Ce2CoAl7Ge4, a member of a recently discovered family of heavy fermion materials Ce2MAl7Ge4 (M=Co, Ir, Ni, or Pd). Previous measurements indicated a strong Kondo interaction as well as magnetic order below TM=1.8K. Our NMR spectral measurements show that the Knight shift K is proportional to the bulk magnetic susceptibility χ at high temperatures. A clear Knight shift anomaly (K¬ χ) is observed at coherence temperatures T∗∼17.5K for H0ĉ and 10 K for H0â at the Co59 site, and T∗∼12.5K at the Al27(3) site for H0â characteristic of the heavy fermion nature of this compound. At high temperatures, the Co59 NMR spin-lattice relaxation rate T1-1 is dominated by spin fluctuations of the 4f local moments with a weak metallic background. The spin fluctuations probed by Co59 NMR are anisotropic and larger in the basal plane than in the c direction. Furthermore, we find (T1TK)-1 T-1/2 at the Co59 site as expected for a Kondo system for T>T∗ and T>TK. Co59 NQR T1-1 measurements at low temperatures indicate slowing down of spin fluctuations above the magnetic ordering temperature TM∼1.8K. A weak ferromagnetic character of fluctuations around q=0 is evidenced by an increase of χT versus T above the magnetic ordering temperature. We also find good agreement between the observed and calculated electric field gradients at all observed sites.