High-pressure study of the phase transition in the itinerant ferromagnetCoS2

Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures

“…5. As seen, the phase line obtained from X-ray diffraction differs significantly from that determined from electrical resistivity, susceptibility and heat capacity data [12]. Obviously, calibrations of the low temperature ruby pressure scale and the scale based on the superconducting transition temperature of lead greatly disagree.…”

“…This situation seems to be not common. For instance, in the case of the helical magnet MnSi a reverse relationship is observed between compressibilities of the coexisting magnetic [12]. Curve 2 was determined by X-ray diffraction and the pressure measured by a ruby sensor.…”

“…Single crystals of CoS 2 were grown by chemical-vapor-transport [12], and some crystals were ground in an agate mortar to prepare a powder sample. X-ray diffraction studies of both crystals and powders of CoS 2 were performed at the HPCAT (16BM-D) beam line of the Advanced Photon Source (APS), Argonne National Laboratory.…”

“…Upon entering the ferromagnetic state CoS 2 becomes a nearly half metal with a significant decrease in the density of states at the Fermi level that is reflected in an increase in the resistivity below T c [7,8]. The temperature-pressure phase diagram of CoS 2 has been studied to high pressures where experiments show that the ferromagnetic transition decreases monotonically and trends to zero at ∼6 GPa [9,10,11,12]. A change from continuous to first-order phase transition with a tricritical point close to ambient pressure was suggested in Refs.…”

“…A change from continuous to first-order phase transition with a tricritical point close to ambient pressure was suggested in Refs. [11,12], which accounts for the absence of a non-Fermi liquid temperature dependence of the resistivity near this critical pressure [12]. The conclusion for a strong first-order quantum-phase transition in CoS 2 was based on indirect arguments [12]; consequently, direct thermodynamic studies are needed to shed light on the evolution and properties of the phase transition in CoS 2 at high pressures.…”