Regensburg 2010 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 16: CE: Quantum-Critical Phenomena 1
TT 16.2: Talk
Tuesday, March 23, 2010, 14:15–14:30, H19
Magnetocaloric effect in Yb(Rh0.93Co0.07)2Si2 — •Alexander Steppke, Niels Oeschler, Cornelius Krellner, Manuel Brando, Christoph Geibel, and Frank Steglich — Max-Planck-Institut für Chemische Physik fester Stoffe Nöthnitzer Str. 40, 01187 Dresden, Germany
The magnetic Grüneisen ratio is defined as ΓH = −(dM/dT)H/CH=1/T(dT/dH)S. Investigation of the magnetocaloric effect (MCE) therefore provides a direct measure of ΓH. At a field-induced quantum critical point (QCP) the critical part of ΓH, ΓHcr, is expected to diverge and to change its sign across the QCP, indicating the accumulation of entropy [1]. The heavy-fermion compound Yb(Rh0.93Co0.07)2Si2 is a prototype system which allows us to study a field-induced QCP [2]. In zero field this compound exhibits two antiferromagnetic transitions at TN=0.4 K and TL=0.07 K, which can be continuously suppressed by small magnetic fields µ0 HN=0.24 T and µ0 HL=0.05 T, respectively. At these fields a maximum in S(H), i.e. a minimum in dT/dH(H), is anticipated. We measured the MCE and the specific heat of Yb(Rh0.93Co0.07)2Si2 down to 0.025 K. Across both TN and TL, ΓHcr changes sign, since dT/dH shows a kink or a minimum. The kink at TN follows the phase boundary TN(H) and disappears for T → 0. However, the minimum at TL is more pronounced in dT/dH, indicating a significant change in entropy. This change in entropy seems to be located near to but not at the phase boundary TL(H).
[1] L. Zhu et al., PRL 91 (2003) 066404; M. Garst and A. Rosch, PRB 72 (2005) 205129
[2] S. Friedemann et al., Nat. Phys. 5 (2009) 465.