P. V. Gurin

Anomalous hall effect in Mn δ-doped GaAs/In0.17Ga0.83As/GaAs quantum wells with high hole mobility

Magnetic and magnetotransport properties of GaAs(δ〈Mn〉)/In0.17Ga0.83As/GaAs quantum wells with different Mn concentrations are studied. The delta-doped manganese layer has been separated from the GaAs quantum well with a spacer with an optimal thickness (3 nm), which has provided a sufficiently high hole mobility (≥103 cm2V−1 s−1) in the quantum wells and their effective exchange with Mn atoms. It is found that the anomalous Hall effect (AHE) is exhibited only in a restricted temperature range above and below the Curie temperature, while the AHE is not observed in quantum wells with quasi-metallic conductivity. Thus, it is shown that the use of the AHE is inefficient in studying magnetic ordering in semiconductor systems with high-mobility carriers. The features observed in the behavior of the resistance, magnetoresistance, and Hall effect are discussed in terms of the interaction of holes with magnetic Mn ions with regard to fluctuations of their potential, hole transport on the percolation level, and hopping conduction.

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.

Ferromagnetism and anomalous transport in GaAs doped by implantation of Mn and Mg ions

GaAs layers doped by implantation of Mn and Mg ions to increase the hole concentration were synthesized and studied. Measurements using a SQUID magnetometer showed that there is ferromagnetism at temperatures as high as 400 K, which is related to the formation of the MnAs and MnyGa1 − y clusters as a result of high-temperature annealing, in addition to the formation of the Ga1 − xMnxAs alloy. The anomalous Hall effect was observed at temperatures in the range from 4.2 to 200 K. As temperature was increased starting with 4.2 K, the negative magnetoresistance with extremely large magnitude transformed into a giant positive magnetoresistance at T ≈ 35 K.

Ferromagnetism and transport in Mn and Mg co-implanted GaAs

We investigated the influence of Mn and Mg co-implantation accompanied by rapid thermal annealing on magnetic and galvanomagnetic properties of p-GaAs. We characterized the samples with SQUID magnetometry and magnetotransport measurements in the temperature interval 4.2 K<T<400 K. Magnetization measurements reveal ferromagnetism up to 400 K (limited by the experimental setup) in all implanted samples. Temperature dependences of resistance, magnetoresistance and Hall effect have been measured in the temperature range 4.2≤T≤300 K. The anomalous Hall effect is visible up to 195 K and shows influence of ferromagnetism of Ga1-xMnxAs solid solution on galvanomagnetic properties of holes. Above this temperature, ferromagnetism survives due to the MnAs and Ga1-xMnx clusters. The magnetoresistance changes from colossal negative to enhanced positive with increasing temperature near T = 35 K.

Transport and ferromagnetism in InGaAs quantum well structures delta-doped with Mn

Samples containing InGaAs quantum wells with p-type conductivity delta-doped by Mn were synthesized and studied. Magnetic moment measurements on a SQUID magnetometer revealed the presence of ferromagnetism at temperatures T from 4.2 to 400 K. Anomalous Hall effect caused by additional sample magnetization was observed at temperatures of from about 30 to 80 K. The Shubnikov-de Haas effect was recorded at 4.2 K. Negative magnetoresistance changed sign for positive at T ≈ 30 K as the temperature increased.

Low-temperature transport and ferromagnetism in GaAs-based structures with Mn

GaAs structures with implanted Mn and, additionally, with Mg for increasing the hole concentration in the implanted Mn layer are synthesized and investigated. SQUID magnetometer measurements revealed the existence of ferromagnetism in the temperature range 4.2 K ≤ T < 400 K, which is associated with the formation of the Ga1−xMnxAs solid solution and MnAs and Ga1−yMny clusters in the sample as a result of rapid high-temperature annealing. At temperatures from 4.2 to approximately 200 K, the anomalous Hall effect associated with additional magnetization of the sample is observed. As the temperature increases from 4.2 K, the colossal negative magnetoresistance is transformed into a positive magnetoresistance at T ≈ 35 K.