Magnetization study on the field-induced quantum critical point in YbRh_2Si_2

TL;DR

This study investigates the quantum critical point in YbRh₂Si₂ using magnetization and Grüneisen ratio measurements, revealing a highly singular behavior of magnetization derivative and phase space regimes of divergent magnetic Grüneisen ratios.

Contribution

It provides detailed experimental insights into the field-induced quantum criticality in YbRh₂Si₂, especially comparing magnetization and thermal expansion data near the QCP.

Findings

Magnetization derivative is more singular than thermal expansion.

Pressure derivative of the field saturates at 0.15 T/GPa as T approaches zero.

The phase space line T* (H) separates regimes with different divergence strengths of Γ_mag.

Abstract

We study the field-induced quantum critical point (QCP) in YbRh$_2$Si$_2$ by low-temperature magnetization, $M(T)$, and magnetic Gr\"uneisen ratio, $\Gamma_{\rm mag}$, measurements and compare the results with previous thermal expansion, $\beta(T)$, and critical Gr\"uneisen ratio, $\Gamma^{cr}(T)$, data on YbRh$_2$(Si$_{0.95}$Ge$_{0.05}$)$_2$. 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, $(dH/dP)_S=V_m\beta/(dM/dT)$ ($V_m$: molar volume), which saturates at $(0.15\pm 0.04)$ T/GPa for $T\to 0$. The line $T^\star(H)$, previously observed in Hall- and thermodynamic measurements, separates regimes in $T$-$H$ phase space of stronger $(\epsilon>1$) and weaker $(\epsilon<1$) divergent $\Gamma_{\rm mag}(T)\propto T^{-\epsilon}$.