A complex modulated magnetic structure in CeNi2Al5 persisting at very low temperatures

The orthorhombic compound CeNi2Al5 is magnetically ordered below 2.6 K. Kondo-type interactions together with strong crystal-electric-field (CEF) effects give rise to a complex magnetic structure: (i) its propagation vector is three dimensional and incommensurate, k = (0.500,0.405,0.083); (ii) the Fourier components of the moment associated with this vector are tilted away from the easy-magnetization axis b. Furthermore, the magnetic structure is double k, as the propagation vectors k = (kx, ky, kz) and k' = (-kx, ky, kz) associated with different magnetic domains are not independent. New experiments have been undertaken to achieve a more precise determination of the magnetic structure. Magnetic peak intensity measurements with higher resolution and polarization analysis have both led to the conclusion that the Fourier component of the magnetic moment deviates slightly from the b-direction. Considering the coupling of the two propagation vectors, the resulting moment describes very flat ellipses with most of the moments very close to b. Neutron diffraction experiments down to 0.4 K have also been performed to investigate the evolution of the magnetic structure at low temperatures. (author)