P. M. Tarasov

Ferromagnetism in a new dilute magnetic semiconductor Sb2-xCrxTe3

Magnetic and galvanomagnetic properties of single crystals of a new dilute magnetic semiconductor p-Sb2−xCrxTe3 (x = 0, 0.0115, 0.0215) are investigated in a temperature range of 1.7–300 K. A ferromagnetic phase with a Curie temperature of TC ≈ 5.8 (x = 0.0215) and 2.0 K (x = 0.0115) is detected. The easy magnetization axis is parallel to the C3 crystallographic axis. Analysis of the Shubnikov-de Haas effect observed in these crystals in strong magnetic fields leads to the conclusion that the hole concentration decreases as a result of doping with Cr. Negative magnetoresistance and the anomalous Hall effect are observed in Cr-doped samples at liquid helium temperature.

Anomalous increase of the thermopower and thermoelectric figure of merit in Ga-doped p-(Bi0.5Sb0.5)2Te3 single crystals

The effect of Ga doping on the temperature dependences (5 K ≤ T ≤ 300 K) of the Seebeck coefficient α, electrical conductivity σ, thermal conductivity coefficient κ, and thermoelectric figure of merit Z of p-(Bi0.5Sb0.5)2Te3 single crystals has been investigated. It has been shown that, upon Ga doping, the hole concentration decreases, the Seebeck coefficient increases, the electrical conductivity decreases, and the thermoelectric figure of merit increases. The observed variations in the Seebeck coefficient cannot be completely explained by the decrease in the hole concentration and indicate a noticeable variation in the density of states due to the Ga doping.

Transport, magnetotransport, and ferromagnetism in diluted magnetic semiconductors

The magnetic properties, Hall effect, and magnetoresistance are discussed for various diluted magnetic semiconductors: In1−xGaxAs quantum well structures, delta-doped with Mn; layers of InAs quantum dots in GaAs, delta-doped with Mn; GaAs structures ion-implanted with Mn and Mg; the thermoelectrics Bi2Te3⟨Fe⟩ and Sb2−xCrxTe3. We investigate the influence of the ferromagnetism that arises in all of those systems on the transport properties, Hall effect, and low-temperature negative magnetoresistance. In Bi2Te3⟨Fe⟩ and Sb2−xCrxTe3 we investigate the influence of Fe and Cr magnetic impurities on the Seebeck coefficient and thermal conductivity.

Anomalous Hall effect and ferromagnetism in the new diluted magnetic semiconductor Sb2−xCrxTe3

The magnetic and galvanomagnetic properties of single crystals of the new diluted magnetic semiconductor p-Sb2−xCrxTe3 (0 ≤ x ≤ 0.02) have been studied in the temperature range 1.7–300 K. A ferromagnetic phase with the Curie temperature Tc ≈ 5.8 K and the maximum Cr content x = 0.0215 has been revealed. The easy magnetization axis is parallel to the C3 crystallographic axis. In the presence of strong magnetic fields, the Shubnikov-de Haas effect has been observed. Analysis of this effect shows that doping with chrome reduces the concentration of holes. Negative magnetoresistance and the anomalous Hall effect are observed at liquid helium temperature.

Thermoelectric properties and ferromagnetism of diluted magnetic semiconductors Sb2 − x Cr x Te3

Thermoelectric properties of single crystals of a new dilute magnetic semiconductor p-Sb2 − xCrxTe3 are studied in the temperature interval 7–300 K. The temperature dependences of the thermal conductivity are measured. The Seebeck coefficient S is found to increase upon doping with Cr. At low temperatures, a ferromagnetic phase with Curie temperature TC ≈ 5.8 K exists for a Cr concentration x = 0.0215, its easy magnetization axis being parallel to the crystallographic axis C3. At T = 4.2 K, a negative magnetoresistance and anomalous Hall effect are observed; in strong magnetic fields, the Shubnikov-de Haas effect is manifested.

Anomalous enhancement of the thermoelectric power in gallium-doped p-(Bi1 − xSbx)2Te3 single crystals

The effect of gallium on the temperature dependences (5 K ≤ T ≤ 300 K) of Seebeck coefficient α, electrical conductivity σ, thermal conductivity k, and thermoelectric efficiency Z of mixed p-(Bi0.5Sb0.5)2Te3 semiconductor single crystals is studied. The hole concentration decreases upon gallium doping; that is, gallium causes a donor effect. The Seebeck coefficient increases anomalously, i.e., much higher than it should be at the detected decrease in the hole concentration. This leads to an enhancement of the thermoelectric power. The observed changes in the Seebeck coefficient indicate a noticeable gallium-induced change in the density of states in the valence band.

Influence of Magnetic Impurities on Thermoelectric Capabilities of Bi2Te3, Sb2Te3, and Bi2Se3

Temperature dependencies of the Seebeck coefficient, electrical conductivity, heat conductivity and the dimensionless thermoelectric figure of merit ZT of p-Bi2Te3, n-Bi2Se3 and Sb2Te3 doped by Fe or Cr have been investigated in the temperature interval 7 < T < 300 K. At T=4.2 K the Shubnikov-de Haas and Hall effects have been measured. By increasing the Fe content, the hole concentration decreases in p-Bi2-xFexTe3, while the electron concentration increases in n-Bi2-xFexSe3. The hole concentration decreases in Sb2-xCrxTe3 with Cr doping. This demonstrates that Fe or Cr act as donors. The Seebeck coefficient increases in p-Bi2-xFexTe3 and Sb2-xCrxTe3 with increasing Fe or Cr content, while it decreases in n-Bi2-xFexSe3.

Thermoelectric properties of Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} single crystals with magnetic impurities

Temparature dependence of Seebeck coefficients S, electrical conductivity, heat conductivity k and dimensionless thermoelectric figure of merit ZT of p-Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and n-Bi{sub 2}Se{sub 3}-doped by Fe or Cr were carried out in the temperature interval 7150 K. - Graphical abstract: Temparature dependence of Seebeck coefficients S, electrical conductivity {sigma}, heat conductivity k and dimensionless thermoelectric figure of merit ZT of p-Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and n-Bi{sub 2}Se{sub 3} doped by Fe or Cr were measured in the temperature interval 7150 K up to ZT=0.4 as shown in figure. Highlights: Black-Right-Pointing-Pointer Fe and Cr act as donors in Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3.} Black-Right-Pointing-Pointer The Seebeck coefficient increases in p-Bi{sub 2-x}Fe{sub x}Te{sub 3} and Sb{sub 2-x}Cr{sub x}Te{sub 3}. Black-Right-Pointing-Pointer Dimensionless figure of merit ZT increased up to 0.4 in Cr-doped Sb{sub 2}Te{sub 3} at T=300 K.

Thermoelectric Properties of Bi2Te3, Sb2Te3and Bi2Se3Single Crystals with Magnetic Impurities.

The thermoelectric properties of single crystals of Fe- or Cr-doped p-Bi2Te3, Sb2Te3, and n-Bi2Se3 are characterized by Seebeck coefficient, electrical conductivity, and heat conductivity measurements between 7 and 300 K.