Transport and Magnetic Study of Gd Ions in Pb_1-ySn_yTe

Abstract

Electric conductivity, Hall effect and magnetic susceptibility of Ρb1-x-ySnyGdxTe mixed crystals with 0.13 < y < 0.93 and 0.001 < x < 0.04 were experimentally studied over the temperature range 4K < T < 300 K. The incorporation of Gd ions into the Pb1-ySnyΤe matrix results in semi-metallic n-type conductivity of the crystals with y < 0.6. For crystals with y > 0.6 one observes only semi-metallic p-type conductivity. We present a model explaining these results in terms of the Sn composition dependence of the location of Gd 2 +/3 + level with respect to the band edges of PbSnGdTe. In recent investigations of magnetic and transport properties of Sn 1 -x Gdx Te it was established that in SnTe Gd forms a resonant donor state with Gd 2 +/3+ energy level located about 0.2 eV below the top of the valence band [1]. Depending on the position of the Fermi level (governed by the concentration of two electrically active centers, Sn vacancies and Gd 3 + ions) with respect to the Gd 2 +/3+ energy level, we expect the Gd ions to be present in SnTe matrix both in the usual 3+ charge state (electron configuration 4f7) and in 2+ state (electron configuration 4f75d1 ).In SnTe Gd shows only limited donor action by partially compensating very high hole concentration due to native acceptor defects [1][2][3]. In related Pb 1 -x Gdx Te semiconducting crystals, Gd shows clear donor character generating the electron concentrations above n 10 20 cm-3 . In PbTe the Gd2+/3+ level is expected to be located far above the bottom of the conduction band. The purpose of our work is to examine the mixed Pb 1 -y Snν Τe crystals with Gd. It is expected that with an increasing content of Sn in Pb 1 -x -y Sn2 Gdx Τe, the Gd2+/3+ energy level will shift down from the conduction band to the valence band via the energy gap. It will result in a smooth change from the n-type to the p-type semi-metallic conductivity via a (possible) semi-insulating state. Similar effects were actually observed in PbSnTe with nonmagnetic In resonant donor [4].We studied a set of bulk Pb 1 -x -y Sny Gdx Τe crystals with y = 0.14, 0.30, 0.50, 0.67, 0.73 and 0.93, and with Gd content up to 4 at.%. We measured the Hall effect and the electric conductivity over the temperature range T = 4-300 K (997)

Ground state splitting ofS8rare earth ions in semiconductors

“…That is why the position of 5d level with respect to the Fermi energy decides whether the mechanism is important or not. For example, as it will be discussed in Section III, for Gd in PbTe this energy is small, of the order of 0.5 eV 13 and the resulting b 4 is of the order of the one observed in experiment, while for Eu ǫ 0 is a few times larger and the calculated splitting is much smaller. In the next Section we describe the model and we derive approximate, analytical result for b 4 .…”

IV-VI Semimagnetic Semiconductors: Recent Developments

“…Apart from the Eu-based IV-VI semimagnetic semiconductors the crystals with Gd such as Sn 1 -x Gd x Te [4,12] and Pb1-x -y Sny Gd x Te [13] are also investigated. The research in this field was recently reviewed in Ref.…”

IV-VI Semimagnetic Semiconductors with Rare Earth Ions

“…One observes experimentally only p-type conductivity in Sn1-x Gd x Te and in Pb1-x-ySnyGd Τe with y > 0.6. The doping with Gd leads to n-type conductivity in Ρb1-x GdxΤe and in Pb1-x -y Sny Gdx Te with y < 0.6 where the Ε0 level is expected to be in the conduction band [34].…”