Classification of materials with divergent magnetic Grüneisen parameter

Abstract

At any quantum critical point (QCP) with a critical magnetic field Hc, the magnetic Grüneisen parameter ΓH, which equals the adiabatic magnetocaloric effect, is predicted to show characteristic signatures such as a divergence, sign change and T /(H − Hc) scaling. We categorize thirteen materials, ranging from heavy fermion metals to frustrated magnets, where such experimental signatures have been found. Remarkably, seven stoichiometric materials at ambient pressure show Hc = 0. However, additional thermodynamic and magnetic experiments suggest that most of them do not show a zero-field QCP. While the existence of a pressure insensitive "strange metal" state is one possibility, for some of the materials ΓH seems influenced by impurities or a fraction of moments which are not participating in a frozen state. To unambiguously prove zero-field and pressure sensitive quantum criticality, a ΓH divergence is insufficient and also the Grüneisen ratio of thermal expansion to specific heat must diverge. arXiv:1609.02013v1 [cond-mat.str-el]

Frustration and quantum criticality

“…In the following we list a few relevant materials and then speculate about possible reasons for this unusual thermodynamic singularity; a detailed exposition of experimental data can be found in Refs. [147,210].…”

Signature of partially frustrated moments and a new magnetic phase in CeNiGe 2

“…Further to substantiate the claim about the role magnetic frustration in this compound, we have calculated the magnetic Gruneisen parameter (Г mag ). In these types of compounds, Г mag is an excellent tool to indentify the supposed magnetic frustration [16]. Generally, Г mag displays a sign change in the frustration regime, signaling entropy accumulate at this regime [17].…”

Unveiling the Physics of the Mutual Interactions in Paramagnets

“…Nowadays, exotic manifestations of matter, like non-Fermi-liquid behavior and unconventional superconductivity [18][19][20][21] , emerging in the immediate vicinity of a quantum critical point (QCP), have been attracting high interest of the community. It is well-established that for a pressure-induced QCP 22,23 , as well as for a finite temperature (T) pressure-induced critical point [24][25][26] , the Grüneisen ratio, i.e., the ratio between thermal expansivity and specific heat at constant pressure, is enhanced upon approaching the critical values of the tuning parameter and it diverges right at the critical point. For a magnetic field-induced QCP 27 the analogous physical quantity to the Grüneisen ratio is the so-called magnetic Grüneisen parameter, hereafter Γ mag 22,28,29 .…”

“…For a magnetic field-induced QCP 27 the analogous physical quantity to the Grüneisen ratio is the so-called magnetic Grüneisen parameter, hereafter Γ mag 22,28,29 . The enhancement of both the Grüneisen ratio and Γ mag in the immediate vicinity of a magnetic field-induced QCP is merely a direct consequence of the high entropy accumulation in that region 22,23 , which in turn is related to the fluctuations of the order parameter. Also, it is well-known that Γ mag quantifies the magneto-caloric effect 30,31 , which in turn enables to change the temperature of a system upon varying adiabatically the external applied magnetic field 22,28,29 .…”