Valence and magnetic instabilities in Sm compounds at high pressures

TL;DR

This study investigates how high pressure affects the electronic and magnetic properties of Sm compounds, revealing pressure-induced insulator-metal transitions and magnetic ordering linked to valence changes.

Contribution

It provides new insights into the pressure-driven electronic and magnetic phase transitions in Sm compounds, highlighting the relationship between valence state and magnetic order.

Findings

Pressure induces insulator-metal transitions in SmS and SmB6.

Magnetic order appears at high pressure near a valence of 2.7.

Metallic Sm shows structural transitions with decreasing magnetic moments.

Abstract

We report on the study of the response to high pressures of the electronic and magnetic properties of several Sm-based compounds, which span at ambient pressure the whole range of stable charge states between the divalent and the trivalent. Our nuclear forward scattering of synchrotron radiation and specific heat investigations show that in both golden SmS and SmB6 the pressure-induced insulator to metal transitions (at 2 and about 4-7 GPa, respectively) are associated with the onset of long-range magnetic order, stable up to at least 19 and 26 GPa, respectively. This long-range magnetic order, which is characteristic of Sm(3+), appears already for a Sm valence near 2.7. Contrary to these compounds, metallic Sm, which is trivalent at ambient pressure, undergoes a series of pressure-induced structural phase transitions which are associated with a progressive decrease of the ordered 4f moment.