A.S. Lagutin

Nanostructures, magnetic semiconductors and spintronics

The aim of this paper is to give a brief overview of recent advances in the area of semiconductor nanomaterials, which represent extremely promising applications for materials with the spin-polarized transport of the charge carriers. It is shown on the basis of the last theoretical and experimental achievements that the development of diluted semiconductors with the controlled disorder and the wide energy gaps as well as the study of their molecular structures are very prospective routes for producing of novel magnetic semiconductors.

Investigation of metamagnetic transitions in the itinerant d subsystem of the intermetallics RCo2 in superstrong magnetic fields up to 300 T

The time derivatives of the magnetization of intermetallic compounds RCo2 (R = Y, Tm, Er, Ho, or Dy) with a metamagnetic subsystem of itinerant d electrons have been measured in pulsed magnetic fields up to 300 T generated by an explosive method. Peaks associated with abrupt demagnetization or magnetization of the d subsystem are found in the field dependences of dM/dH. The results obtained are compared with theoretical estimates and the values derived for the critical fields from measurements performed on substituted compounds.

Magnetic properties of GaAs/δ〈Mn〉/GaAs/InxGa1 − xAs/GaAs quantum wells

The field and temperature dependences of the magnetization of GaAs/δ〈Mn〉/GaAs/InxGa1 − xAs/GaAs quantum wells with the δ〈Mn〉 layer separated from the well by a 3-nm GaAs spacer have been studied in the temperature range of 3–300 K in a magnetic field up to 6 T. An external magnetic-field-induced phase transition to a ferromagnetic state with a magnetization hysteresis loop shifted from a zero magnetic field has been found to occur at a temperature below 40 K. A theoretical model is proposed that implies the coexistence of ferromagnetically and antiferromagnetically ordered regions within the GaAs layers.

Faraday effect in an Ising ferrimagnet in megagauss fields

Abstract Faraday rotation measurements were performed on a Ho0.7Y2.3Fe5O12 single crystal at 77K and B□[111] in ultrahigh pulsed magnetic fields (up to 350 T). Several anomalies of the rotation were observed in the 15–50 T region, but only a slight increase of the magnitude of the Faraday effect was found above 150 T. A model is proposed to interpret the results, taking into account both the para- and diamagnetic contributions of rare earth and ferrous subsystems.

Magnetic properties of the HoMn2Ge2 intermetallic compound

The magnetic properties of a tetragonal intermetallic compound, namely, HoMn2Ge2, are investigated experimentally and theoretically. The experimental temperature dependences of the initial magnetic susceptibility and the lattice parameters are obtained in alternating and static magnetic fields. The magnetization curves are measured in strong magnetic fields up to 50 T. The parameters of the crystal field and Ho-Mn and Mn-Mn exchange interactions are determined, and the temperature dependence of the magnetic field of the phase transition from an antiferromagnetic phase to a ferromagnetic phase in a magnetic field aligned along the tetragonal axis is calculated.

A new quasi-Ising magnet

We have performed measurements of the magnetization and differential magnetic susceptibility of Dy0.62Y2.38Fe5O12 single crystals in pulsed magnetic fields up to 45 T at liquid-helium temperature for three orientations of the external field: H‖[100], H‖[110], and H‖[111]. It was found that the magnetization reversal in the rare-earth magnetic subsystem occurs via several phase transitions, whose number depends on the direction of the external field, as is characteristic for Ising magnets. The anomalies in the field dependences of the magnetization are interpreted on the assumption of quasi-Ising ordering of the rare-earth ions.

Microwave spectroscopy of multisublattice magnet in high pulsed magnetic fields

Experimental results of the microwave absorption are presented for the HoxY3−xFe5O12 single crystal (x < 0.5) in pulsed fields up to 30 T and in the frequency range 28–110 GHz and temperature range 4.2–180 K. A large number of resonances were observed close to and far from the magnetic phase transitions. It was shown that high field resonances are caused by the existence of both the static and dynamic magnetic analogs of the Jahn-Teller effect.

Magnetic phase transitions in 3d-4f intermetallic induced by ultra strong magnetic fields

Abstract The time derivatives of magnetisation for intermetallics RCo 2 (R  Y, Lu, Tm, Er, Ho, Dy) with metamagnetic itinerant d-subsystem were measured in pulsed magnetic fields up to 300 T using an explosive-driven generator. Sharp maxima on d M /d t connected with a jump-like magnetisation or demagnetisation of the d-subsystem were observed. The results obtained are compared with estimates made from the measurements on substituted compounds.

Reducing Humidity Response of Gas Sensors for Medical Applications: Use of Spark Discharge Synthesis of Metal Oxide Nanoparticles

The application of gas sensors in breath analysis is an important trend in the early diagnostics of different diseases including lung cancer, ulcers, and enteric infection. However, traditional methods of synthesis of metal oxide gas-sensing materials for semiconductor sensors based on wet sol-gel processes give relatively high sensitivity of the gas sensor to changing humidity. The sol-gel process leading to the formation of superficial hydroxyl groups on oxide particles is responsible for the strong response of the sensing material to this factor. In our work, we investigated the possibility to synthesize metal oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in gas phase by spark discharge, enabling the reduction of the hydroxyl concentration on the surface and allowing the production of tin dioxide powder with specific surface area of about 40 m2/g after annealing at 610 °C. The drop in sensor resistance does not exceed 20% when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is a factor of 8 with very short response time of about 1 s. The sensor response was tested in mixtures of air with hydrogen, which is the marker of enteric infections and the marker of early stage fire, and in a mixture of air with lactate (marker of stomach cancer) and ammonia gas (marker of Helicobacter pylori, responsible for stomach ulcers).

Linear dynamics of a magnetic subsystem in a quasi-Ising magnet

Microwave absorption at frequencies from 37 to 85 GHz was studied for a Dy0.3Y2.7Fe5O12 single crystal in pulsed magnetic fields of up to 30 T at T=4.2 K. The magnetic field was aligned with the [100] direction. For the fields above 4 T, several soft magnetic-resonance modes were observed, most of them being caused by the static phase transitions induced by a strong external magnetic field. The field-independent absorption lines away from the points of phase transition may be due to the dynamic Jahn-Teller magnetic effect.