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Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Correlated Electrons: Quantum-Critical Phenomena 2

TT 22.7: Talk

Wednesday, March 25, 2009, 11:30–11:45, HSZ 03

Low-temperature magnetic phase diagram of the heavy-fermion compound YbCo2Si2 — •Luis Pedrero, Christoph Klingner, Manuel Brando, Christoph Geibel, and Frank Steglich — Max-Planck-Institut für Chemische Physik fester Stoffe Nöthnitzer Str. 40, 01187 Dresden, Germany

We report on the first high-resolution DC magnetization M(H,T) measurements on a single crystal of YbCo2Si2. M was measured down to 50 mK and fields up to 12 T with the field Hc axis. The magnetic phase diagram of YbCo2Si2 was deduced from the isothermal curves along with susceptibility and heat-capacity measurements.
Two antiferromagnetic phase transitions have been detected at TN=1.65 K and TL=0.9 K. The signatures at TN suggest that the phase transition is 2nd order and it is suppressed by a field µ0HN=1.9 T. At TL latent heat has been observed in the heat capacity in zero field and hysteresis effects in the M vsH confirm the 1st order nature of the transition. The entropy below both transitions and the M value at HN point to a local character of the Yb 4f quasi-hole, resulting in a very small Kondo temperature compared to the one in YbRh2Si2 [1]. However, the data at 50 mK reveals the presence of a kink in M vsH at µ0HN=10.6 T, very similar to the one observed YbRh2Si2 at µ0HN=9.9 T, where a suppression of the Kondo fluctuations or a Lifshitz transition have been proposed [1,2]. The TH phase diagram as well as the nature of the high-field transition will be discussed.

[1] Y. Tokiwa et al. Phys. Rev. Lett. 94, 226402 (2005).

[2] P. M. C. Rourke et al., submitted (2008).

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