Pressure-Induced Valence Transition in Antiferromagnet EuRh₂Si₂

Abstract

Considering the unique properties of EuRh 2 Si 2 from the viewpoint of the Eu valence, we have examined its physical properties under external pressure. At ambient pressure, EuRh 2 Si 2 is an antiferromagnet with a Néel temperature T N of 25 K, and the Eu ion is in the divalent state. The application of pressure up to 0.84 GPa slightly shifts T N toward higher values. Under pressures higher than 1.00 GPa, an abrupt first-order valence transition emerges simultaneously with the disappearance of antiferromagnetism. For P ¼ 1:17 GPa, the valence change associated with valence transition is roughly estimated to be $0:19 from the thermal expansion anomaly. The valence transition temperature T v increases rapidly with increasing pressure. The temperature-pressure phase diagram of EuRh 2 Si 2 is very similar to those of the other systems showing pressure-induced valence transition.

Unique Fermi Surface and Emergence of Charge Density Wave in EuGa4 and EuAl4

“…Interestingly the valence of some Eu compounds is changed by temperature, magnetic field and pressure. For example, the Eu-divalent electronic state in EuRh 2 Si 2 is changed into a nearly trivalent one under pressure, where a critical pressure is P c 1 GPa [1]. In the case of EuNi 2 P 2 , a nearly Eu-divalent electronic state at room temperature is changed into a heavy fermion state at low temperatures via the Kondo effect, where an electronic specific heat coefficient is γ = 100 mJ/(K 2 ·mol) and the Kondo temperature is T K = 80 K [2].…”

Fermi Surface and Magnetic Properties of Antiferromagnet EuBi3

“…Therefore, valence instability often occurs in Eu compounds, from a divalent electronic state of Eu 2þ (4f 7 : S ¼ 7=2, L ¼ 0, and J ¼ 7=2) at high temperatures to a nearly trivalent electronic state (4f 6 in Eu 3þ : S ¼ L ¼ 3, and J ¼ 0) at low temperatures, depending on the magnetic field and pressure. [4][5][6] Here, S, L, and J are the spin, orbital, and total angular momenta, respectively. EuBi 3 is a divalent compound and orders antiferromagnetically below a Néel temperature T N ' 7:5 K, which was identified by electrical resistivity, magnetic susceptibility, and specific heat experiments.…”

Antiferromagnetic Order of EuGa4Probed by Mössbauer Spectroscopy

“…On the other hand, the trivalent Eu state is non-magnetic (J = 0, S = L = 3). For example, the recent experimental result of EuRh 2 Si 2 with the tetragonal structure is typical [1]. The electronic state of EuRh 2 Si 2 is divalent at ambient pressure, and orders antiferromagnetically below a Néel temperature T N = 23 K. The application of pressure up to 0.84 GPa slightly shifts T N toward higher values.…”