Regensburg 2000 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 7: Postersitzung I: Amorphe- und Tunnelsysteme (1-8), Mesoskopische Systeme (9-21), Schwere Fermionen (22-32), Kernmagnetismus (33-34), Josephson-Kontakte und SQUIDs (35-45), TT-Detektoren und Kryotechnik (46-49)

TT 7.30: Poster

Montag, 27. März 2000, 14:30–18:00, A

Magnetic Behaviour of the New Kondo Lattice Systems Ce₂M₃Ge₅ (M = Rh, Ir, Ni) — •Z. Hossain¹, S. Hamashima², K. Umeo², and T. Takabatake² — ¹Max-Planck-Institut für Chemische Physik fester Stoffe, Bayreuther Str. 40, 01187 Dresden — ²Department of Quantum Matter, ADSM, Hiroshima University, 739 8526 Japan

We report physical properties of Ce₂M₃Ge₅ (M = Rh, Ir, Ni). Occurrence of peaks in the susceptibility and heat capacity suggests Ce₂M₃Ge₅ (Rh, Ir) undergo antiferromagnetic ordering below T_N 5.5 K and 9.5 K, respectively. Ce₂Ni₃Ge₅ shows two magnetic transitions at 4.5 K and 5.1 K. The magnetic contribution to the resistivity varies as -lnT in two distinct temperature regions. This type of behavior is suggestive of Kondo effect in presence of crystal field effect. A very large drop in resistivity below T_N in Ce₂Rh₃Ge₅ and Ce₂Ir₃Ge₅ is attributed to the combined effect of the decrease in the spin disorder scattering and development of coherence in the Kondo Lattice. The temperature dependence of resistivity and specific heat below 4 K reveal the appearance of spin wave-gap in Ce₂Ni₃Ge₅. The magnetic entropy at T_N reaches 0.5Rln2, 0.65Rln2 and 0.65Rln2 for Rh, Ir and Ni compounds respectively, which suggest that the ground state is a doublet and there is a considerable reduction of the magnetic moments due to presence of Kondo effect. The large value of linear coefficient of the heat capacity ( 150 mJ/mol Ce K²) for Ce₂M₃Ge₅ ( M = Rh, Ir) suggests that they are moderate heavy fermion compounds. The Kondo temperatures are in the range 5-10 K. The magnetoresistance in the paramagnetic region is negative which is characteristic of the Kondo effect.