Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce(n)Rhln(3n+2) (n=1 or 2) - art. no. 144411

We have measured the field-dependent heat capacity in the tetragonal anti f erromagnets CeRhIn5 and Ce2RhIn8, both of which have an enhanced value of t he electronic specific heat coefficient gamma similar to 400 mJ/mol Ce K-2 above T-N. For T<T-N, the specific heat data at zero applied magnetic field are consistent with the existence of an anisotropic spin-density wave open ing a gap in the Fermi surface for CeRhIn5, while Ce2RhIn8 shows behavior c onsistent with a simple antiferromagnetic magnon. From these results, the m agnetic structure, in a manner similar to the crystal structure, appears mo re two dimensional in CeRhIn5 than in Ce2RhIn8 where only about 12% of the Fermi surface remains ungapped relative to 92% for Ce2RhIn8. When B<paralle l>c, both compounds behave in a manner expected for heavy-fermion systems a s both T-N and the electronic heat capacity decrease as field is applied. W hen the field is applied in the tetragonal basal plane (B parallel toa), Ce RhIn5 and Ce2RhIn8 have very similar phase diagrams which contain both firs t- and second-order field-induced magnetic transitions.