Atomic disorder and canted ferrimagnetism in the TbCr6Ge6 compound. A neutron study

[摘要] A structure determination using high resolution neutron powder data (difference Fourier maps) has shown that the hexagonal compound TbCr6Ge6 (P6/mmm) is a partly disordered derivative of the HfFe6Ge6-type structure where a part of the Tb atoms at 1(a) (0,0,0) and a part of the Ge-2 atoms at 2(e) (0,0,0.347) populate intermediate lattice positions which are shifted by c/2. The observed atomic disorder modifies the R-R interactions as well as the crystal field, leading to an ordered state and easy axis for the Tb moments different from that found for the (fully ordered) isomorphic TbMn6Ge6 compound. As the Cr-Cr interaction is very weak the ordering is dominated by the R-R interaction. TbCr6Ge6 orders below T-c=10.3 K with a canted ferrimagnetic moment arrangement where the moments of the Tb and Cr sublattices have different orientations making an angle of 25(2) deg. and 143(7) deg. with the c-axis respectively. The ordered moment values of the two sublattices at 1.5 K are 8.74(1) mu(B)/Tb and 0.48(10) mu(B)/Cr. The net magnetic moment of the structural model proposed is found to be in satisfactory agreement with results of magnetic measurements reported earlier.

[发布日期] 1997-06-20