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

Original · EN

We study the field-induced quantum critical point (QCP) in YbRh₂Si₂ by low-temperature magnetization, M(T), and magnetic Grüneisen ratio, Γ mag, measurements and compare the results with previous thermal expansion, β(T), and critical Grüneisen 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 Γ mag(T)∝ T⁻ε.