Configuration of Sm in SmB6

Abstract

SmB6 has been found to show no magnetic ordering down to a temperature of 0.35°K, in spite of the fact that the other rare earth hexaborides showed ordering in the neighborhood of 10–20°K.1,2 We interpret this to mean that the Sm ion is in its nonmagnetic divalent configuration at low temperatures. Direct evidence for the changing electronic configuration of Sm from trivalent to divalent with decreasing temperature has now been found by the observation that the size of the unit cell goes through a minimum near 150°K. The magnetic susceptibility, which has been measured between 1° and 800°K shows evidence for the presence of primarily Sm+3 above 300°K and Sm+2 below 100°K. Below 40°K the resistivity of SmB6 increases as T decreases with an activation energy of about 0.002 eV. Such semiconducting behavior is to be expected from divalent Sm in the hexaboride lattice.

X-ray atomic orbital analysis of 4f and 5d electron configuration of SmB6 at 100, 165, 230 and 298 K

“…(iii) Elongation of lattice parameters below 150 K in SmB 6 , as reported earlier by Menth, Buehler, Levinstein & Geballe (1969), may be explained by the occupied 5d 5/2 À 8 orbitals at 100 K, although the accuracy of our measurement indicates that the elongation is stopped on lowering the temperature to 165 K.…”

“…The temperature factors of Sm and B were also reduced four or five times more than their errors with temperature. The lattice parameter of SmB 6 was reported to be minimum near 150 K by Menth, Buehler, Levinstein & Geballe (1969) and Mercurio et al (1976). It was attributed to the change in ratio of Sm 3+ and Sm 2+ (Tarascon et al, 1980).…”

Temperature dependence of the samarium oxidation state in SmB6 and Sm1-xLaxB6

“…Furthermore previous Môssbauer resonance and X-ray absorption experiments performed respectively down to l.l K and 150 K had not indicated significant variations of the SM2, : Sm 3 + ratio [3,4,5]. On the other hand, the lattice-parameter measurements carried out previously by us between 300 K and 4.2 K suggested a samarium valence change in SmB6 [5,11].…”

“…Samarium hexaboride 5mB6 has attracted much experimental and theoretical attention in the last few years. SmB6 is a homogeneous mixed valent compound in which the Sm2+ : Sm3+ ratio at room temperature has been estimated to be about 4 : 6 from magnetic susceptibility, Môssbauer resonance measurements, LIII X-ray absorption, and X-ray photoelectron spectroscopy (XPS) [1][2][3][4][5][6][7][8][9][10].…”

Buffer-layer-enhanced growth of a single-domain LaB6 (1 0 0) epitaxial thin film on a MgO (1 0 0) substrate via pulsed laser deposition

“…Hexaborides possess a wide range of interesting electronic and magnetic properties, including mixed valence [1], heavy fermion [2], metallic [3][4][5][6][7], superconducting [8], and semiconducting [9] behaviors. Previously, considerable experimental and theoretical works have been performed to understand the electrical behavior, especially for bulk samples of LaB 6 .…”