ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
Depending on the H concentration at the octahedral (O) sites, x(O), various tetragonal phases, due to H ordering, are observed in the Ce hydride at low temperatures. While our single crystal work showed that the tetragonal phase for H/Ce≈2.7, corresponding to x(O)≈3/4, is only stable in a region of x(O)=±0.05, the other one was believed to be caused by a single H ordering process for 0.15≤x(O)≤0.5 up to now. However, strong discrepancies in the structure were reported from different neutron diffraction studies. We have studied both the structural H ordering and the magnetic ordering by neutron diffraction work for 0.2≤x(O)≤0.5. It will be shown that the H ordering for x(O)=1/4 and 1/2 are completely different (Space groups: I4/mmm and I41/amd, respectively). Accordingly, for x(O)=1/2 the Ce atoms are crystallographically identical, while for x(O)=1/4 two different Ce atoms are present in the lattice. Also the magnetic order is completely different for the two phases. For x(O)=0.5, a commensurate magnetic phase appears below TN≈3.5 K. The structure is described by a canted ferromagnet with μF=1.3 μB/Ce atom along the c axis and μAF=1.1 μB/Ce atom within the plane normal to c. On the other hand, for 0.2≤x(O)≤0.25, an incommensurate AF phase with a long period, described by the wave vector τ=(0.12, 0.12, 0), is obtained at 1.4 K. Above 2.6 K, this phase is progressively replaced by the commensurate lines discussed before. For x(O)=0.265, the two phases coexist at 1.4 K, while for x(O)=0.28 only the commensurate phase is retained. Apparently, the long period phase is characteristic of the ideal H ordering around x(O)=1/4, whereas it is strongly affected by the H occupation of the new positions for higher concentrations.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.356721
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