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

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 Neel temperature T-N (approximate to 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 approximate to 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

Exploring high temperature magnetic order in CeTi1-xScxGe

“…Beyond a critical point, the formation of a quasiquartet enhances the exchange interaction between Ce-planes with the consequent growth of the ordering temperature. Similar behavior was recently observed in CeCoSi under pressure showing a high temperature magnetic order also attributed to a quasiquartet level formation [19]. This facts are ascribed into a scenario of a change in the magnetic dimensionality from 2D type to 3D and the appearance of spin density waves with incommensurate wave vector.…”

Odd-Parity Multipoles by Staggered Magnetic Dipole and Electric Quadrupole Orderings in CeCoSi

“…While changing temperature and pressure, CeCoSi undergoes two phase transitions: the antiferromagnetic (AFM) order at T N = 8.8 K at ambient pressure 24,25) and the hidden order, the latter of which dominantly appears under pressure. [26][27][28] Recently, the experiment implies that the hidden order under pressure corresponds to the antiferroquadrupole (AFQ) order, 27, 28) since it shows similar behavior to the AFQ phase observed in CeB 6 and CeTe. [29][30][31][32][33][34][35] Interestingly, the unit of the staggered AFM and AFQ orders in CeCoSi accompanies the cluster-type odd-parity multipoles, as the staggered alignment of the even-parity multipoles at two Ce sites breaks the global inversion symmetry.…”

Magnetic Properties in Tetragonal Antiferromagnet CeCoSi

“…2(b), where data are partly cited in refs. [9] and [10]. In CeCoSi, there are two phase transitions at zero magnetic field: T 0 ∼ 12 K from the paramagnetic state (phase I) to the possible multipole ordered state (phase II), and T N = 9.4 K for the AFM ordered state (phase III).…”

“…CeCoSi and related materials have been studied for hydrogen storage property [7], and a catalyst for ammonia synthesis [8]. At low temperatures, an antiferromagnetic (AFM) ordering of Ce-4 f electrons takes place at T N ∼ 9.5 K [9]. Lengyel et al examined pressure effects on CeCoSi, and reported a unique pressure−temperature (P − T ) phase diagram.…”

“…From the characteristics of the magnetization and the P − T phase diagram, we concluded that the intermediate phase for T N < T < T 0 is a part of the pressure induced ordered phase. A possibility of an antiferroquadrupolar (AFQ) ordering due to Ce-4 f electrons has been discussed for the origin of the intermediate phase [9][10][11]. Since there is no space-inversion symmetry on the Ce site, odd-parity multipoles could also contribute to form the phase transition at T 0 in addition to even-parity ones [10,11].…”