Temperature-pressure phase diagram of CeCoSi: Pressure-induced high-temperature phase

E. Lengyel, M. Nicklas, N. Caroca-Canales, and C. Geibel

Phys. Rev. B 88, 155137 – Published 30 October 2013

Abstract

We have studied the temperature-pressure phase diagram of CeCoSi by electrical-resistivity experiments under pressure. Our measurements revealed a very unusual phase diagram. While at low pressures no dramatic changes and only a slight shift of the Neél temperature $T_{N}$ ( $\approx$ 10 K) are observed, at about 1.45 GPa a sharp and large anomaly, indicative of the opening of a spin-density wave gap, appears at a comparatively high temperature $T_{S} \approx 38$ K. With further increasing pressure, $T_{S}$ shifts rapidly to low temperatures and disappears at about 2.15 GPa, likely continuously in a quantum critical point, but without evidence for superconductivity. Even more surprisingly, we observed a clear shift of $T_{S}$ to higher temperatures upon applying a magnetic field. We discuss two possible origins for $T_{S}$ : magnetic ordering of Co and a metaorbital type of transition of Ce.