Valence and magnetic instabilities in Sm compounds at high pressures

Abstract

We report on the study of the response to high pressures of the electronic and magneticproperties of several Sm-based compounds, which span at ambient pressure the whole range ofstable charge states between the divalent and the trivalent. Our nuclear forward scatteringof synchrotron radiation and specific heat investigations show that in both golden SmS andSmB6 the pressure induced insulator to metal transitions (at 2 and –7 GPa, respectively) are associated with the onset of long-range magnetic order, stable up toat least 19 and 26 GPa, respectively. This long-range magnetic order, which is characteristic ofSm3+, appears already for a Sm valence near 2.7. In contrast to these compounds, metallic Sm,which is trivalent at ambient pressure, undergoes a series of pressure induced structuralphase transitions which are associated with a progressive decrease of the ordered 4fmoment.