Laves phase compounds crystal field

Fig. 59. Left Angular dependence of the TF = 0.15T p.SR depolarization rate for a single crystal of CeAlj at temperatures well above 3.5 K). The crystal is rotated around the (110) axis. An angle of 90" corre nds to a field applied along (100). The top part shows the experimental result for two tenqieratures, die bottom part corresponding dipolar sum calculations for three different tetrahedral muon stopping sites. Right Tenqierature dependence of the muon spin depolarization rate in three CIS Laves-phase compounds. The step around 80K signals the onset of muon mobility (see text). From Hartmann et al. (1989, 1990b).

There are several dozen metallic AB2 compounds called Laves phases that are superconducting they have either cubic or hexagonal crystal structures. Some have critical temperatures above 10 K and high upper critical magnetic fields Bc2- For example, Zri/2Hfi/2V2 has rc = 10.1K, B 2 = 24 T, and a compound with a different Zr/Hf ratio has similar and Bc2 values with the critical current density Jc 4 X 10 A/cm. These materials also have the advantage of not being as hard and brittle as some other intermetallics and alloys with comparable transition temperatures. 

RNi2 compounds crystallize in the cubic Laves phase structure. Because of the simplicity of structure and the ease of preparation and characterization these materials have been extensively studied. From magnetic studies of this family of compounds, Skrabek and Wallace (55) established that nickel moment is zero in the ordered state and moreover that the moment of the rare earth atom is considerably reduced in comparison to that expected for a free trivalent rare earth ion. Bleaney (86) and Skrabek and Wallace (55) have interpreted this decrease in the saturation moment as arising from partial crystal field quenching of the orbital contribution to the total moment. In this respect the RNi2 compounds behave like the RA12 compounds described in an earlier section above. 

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