Magnetization study on the field-induced quantum critical point in YbRh2Si2

Abstract

We study the field-induced quantum critical point (QCP) in YbRh2Si2 by low-temperature magnetization, M(T), and magnetic Grüneisen ratio, Γmag, measurements and compare the results with previous thermal expansion, β(T), and critical Gr̈neisen ratio, Γcr (T), data on YbRh2(Si0.95Ge0.05)2. In the latter case, a slightly negative chemical pressure has been used to tune the system towards its zero-field QCP. The magnetization derivative –dM/dT is far more singular than thermal expansion, reflecting a strongly temperature dependent pressure derivative of the field at constant entropy, (dH/dP)s = Vmβ/(dM/dT) (Vm: molar volume), which saturates at (0.15±0.04) T/GPa for T → 0. The line T*(H), previously observed in Hall-and thermodynamic measurements, separates regimes in T-H phase space of stronger (ε > 1) and weaker (ε < 1) divergent Γmag(T) ∝ T−ε.