Anomalous change of the magnetic moment direction by hole doping in CeRu2 Al10

We present a detailed investigation of the hole (3% Re) doping effect on the polycrystalline CeRu2Al10 sample by magnetization, heat capacity, resistivity, muon spin relaxation (μSR), and neutron scattering (both elastic and inelastic) measurements. CeRu2Al10 is an exceptional cerium compound with an unusually high Néel temperature of 27 K. Here we study the stability of the unusual magnetic order by means of controlled doping, and we uncover further surprising attributes of this phase transition. The heat capacity, resistivity, and μSR measurements reveal an onset of magnetic ordering below 23 K, while a broad peak at 31 K (i.e., above TN) has been observed in the temperature dependent susceptibility, indicating an opening of a spin gap above TN. Our important finding, from the neutron diffraction, is that the compound orders antiferromagnetically with a propagation vector k=(1,0,0) and the ordered state moment is 0.20(1) μB along the b axis. This is in sharp contrast to the undoped compound, which shows AFM ordering at 27 K with the ordered moment of 0.34-0.42 μB along the c axis. Similar to CeRu2Al10 our inelastic neutron scattering study on the Re-doped compound shows a sharp spin gap-type excitation near 8 meV at 5 K, but with slightly reduced intensity compared to the undoped compound. Further the excitation broadens and shifts to lower energy (≤4 meV) near 35 K. These results suggest that the low temperature magnetic properties of the hole-doped sample are governed by the competition between the anisotropic hybridization effect and the crystal field anisotropy as observed in hole-doped CeOs2Al10.