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

The orthorhombic compound CeNi2Al5 is magnetically ordered below 2.6 K. Kon dotype interactions together with strong crystal-electric-field (CEF) effec ts give rise to a complex magnetic structure: (i) its propagation vector is three dimensional and incommensurate, Ic = (0.500, 0.405. 0.083); (ii) the Fourier components of the moment associated with this vector are tilted aw ay from the easy-magnetization axis b. Furthermore, the magnetic structure is double Ic, as the propagation vectors k = (k(x), k(y), k(z)) and k' = (- k(x), k(y), k(z)) associated with different magnetic domains are not indepe ndent. New experiments have been undertaken to achieve a more precise determinatio n of the magnetic structure. Magnetic peak intensity measurements with high er resolution and polarization analysis have both led to the conclusion tha t the Fourier component of the magnetic moment deviates slightly from the b -direction. Considering the coupling of the two propagation vectors, the re sulting moment describes very Bat ellipses with most of the moments very cl ose to b. Neutron diffraction experiments down to 0.4 K have also been perf ormed to investigate the evolution of the magnetic structure at low tempera tures.