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

Abstract

Abstract. The volume change and heat capacity at the ferromagnetic phase transition in CoS 2 were measured at high pressures using X-rays generated by the Argonne synchrotron light source and by ac-calorimetry, respectively. The transition entropy, calculated on the basis of these experimental data, drops along the transition line due to quantum degradation, as required by Nernst's law. The volume change increases strongly along the transition line, which is explained by specifics of the compressibility difference of coexisting phases that results from nearly half metallic nature of the ferromagnetic phase of CoS 2 .

Raman studies of nearly half-metallic ferromagnetic CoS2

“…This leads to an enhancement of the direct Coulomb ion-ion repulsive interactions due to the decreased screening ability of the electronic gas and the influences of the stretching modes of the vibrational spectra of CoS 2 . A decrease of the compressibility and electronic heat capacity in the ferromagnetic phase of CoS 2 supports the above conclusion [9]. Note that a decrease of compressibility is also observed in the ferromagnetic halfmetallic phase of CrO 2 [30].…”

“…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]. An influence of half-metallicity on the thermodynamic properties and phase diagram of CoS 2 was reported in [9]. So one might expect that the lattice dynamic of CoS 2 should somehow reveal this effect as well.…”

New developments in micro-X-ray diffraction and X-ray absorption spectroscopy for high-pressure research at 16-BM-D at the Advanced Photon Source

“…The beamline 16-BM-D is one of four beamlines operated by the High Pressure Collaborative Access Team (HPCAT) at the Advanced Photon Source (APS) and is dedicated to highpressure research in physics, chemistry, materials science, and earth and planetary sciences using micro-X-ray diffraction (micro-XRD), X-ray absorption spectroscopy (XAS), and anomalous X-ray scattering/diffraction. 1 The beamline has been optimized mainly for micro-XRD techniques since it became operational in 2006 and has made significant contributions to many areas of science, for example, pressureinduced phase transition, [2][3][4][5][6] structure determination, [7][8][9] structure and property correlation, [10][11][12][13] superconductivity, [14][15][16][17] and amorphous materials. [18][19][20][21] In the course of continuous development, many discoveries have been made, including high-pressure phases, [22][23][24][25][26][27][28] properties, 29,30 and processes.…”

Evidence of kinetic arrest in Se doped CoS2

“…Recent work of Otero−Leal ‡ E-mail : rrawat@csr.res.in et al suggest that it is weakly first order and T C lies close to tricriticality [19]. The transition vanishes around 5-6 GPa [16,15] and under higher pressures the application of magnetic field result in itinerant metamagnetic behaviour [10]. Interestingly the effect of Se substitution for S, which increases the unit cell volume, is nearly same as that of pressure i.e.…”

“…due to reduction in the density of state at Fermi level of minority spin band [13,14]. With the application of pressure, T C is shifted to low temperature and appearance of thermal hysteresis indicates first order nature of the transition [15,16,10,17,18]. The nature of transition in CoS 2 under ambient pressure, itself has been a subject matter of debate [19,14,10,16].…”