Kh. T. Igamberdiev

Critical behavior of Zn1−xMnxO doped by nitrogen

The thermal diffusivity measurements have been used to study the magnetic phase transition in Zn0.95Mn0.05O doped by nitrogen. The critical parameters of the ferromagnetic-paramagnetic transition have been obtained through the analysis of the inverse of the thermal diffusivity near the Curie temperature. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat, the critical exponent α has been determined. The results are consistent with the three-dimensional Heisenberg model for the magnetic phase transition.

Magnetic phase transition in Zn1−xMnxO doped by nitrogen

The specific heat measurement was used to study the magnetic phase transition in Zn0.95Mn0.05O. The magnetization dependencies on the magnetic field, M(H) curve, and on the temperature, M(T) curve measured by superconducting quantum interference device, indicate the ferromagnetic-paramagnetic phase transition in Zn0.95Mn0.05O doped by nitrogen has a Curie temperature of about 80 K. The temperature dependence of the specific heat reveals a pronounced λ shaped peak at 75 K for the nitrogen-doped sample. Such dependencies indicate a well defined second-order phase transition in this sample.

Crossover critical behavior of Ga 1-xMn xAs

The critical behavior of Ga1-xMnxAs in a close vicinity of the Curie temperature was experimentally studied by using the thermal diffusivity measurements. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat, the critical exponent {\alpha} for the samples investigated has been determined. With approaching close to the critical temperature, the crossover from the mean-field-like to the Ising-like critical behavior has been observed. From the crossover behavior the values of the Ginzburg number and the exchange interaction length in Ga1-xMnxAs with different concentrations of Mn were determined.

INFLUENCE OF STRUCTURAL DEFECTS ON THE THERMOPHYSICAL AND MAGNETIC PROPERTIES OF POLYANILINE

The temperature dependences of the thermophysical and paramagnetic properties of polyaniline that contains variously structured impurity centers have been investigated. The results obtained have been explained on the basis of the theory of phase transitions of second order.

Heat transport in ZnO/PMMA nanocomposites

The thermal conductivity of zinc oxide-polymethyl methacrylate (PMMA) composites has been measured. Using theoretical models, the thermal resistance of ZnO-NW/PMMA interfaces (NW is the nanowire) and the critical particle radius above which the composite thermal conductivity can be increased have been estimated. Based on these measurements, the dependence of the thermal conductivity of zinc oxide nanowires on their diameter has been determined.

Study of Weak Ferromagnetism in Zn1‐xCoxO

The temperature dependencies of the magnetization and the thermal diffusivity of Zn1‐xCoxO have been conducted. Zn1‐xCoxO (x = 0.03) thin films were deposited on Si (100) substrates by using ultrasonic spray pyrolysis. Magnetization M(H) measurements show a hysteresis loop which indicates an existence of ferromagnetism in Zn0.97Co0.03O. However, the magnetic moment per Co ion is much lower than expected. A comparison of M(T) measured at zero‐field‐cooled (ZFC) and field‐cooled (FC) conditions shows a superparamagnetic like behavior and the blocking temperature is about 130K. Temperature dependence of the thermal diffusivity of Zn0.97Co0.03O shows a pronounced λ shaped minimum at 130K, which indicates an existence of a second‐order phase transition at this temperature. The low value of the phase transition entropy shows that only a small part of Co ions is involved in ferromagnetic ordering.

Thermal properties of manganese-doped ZnO polycrystalline films

The thermal conductivity and heat capacity of manganese-doped zinc oxide polycrystals have been studied in the temperature range 30–300 K. A substantial influence of the secondary phase or MnO clusters formed as a result of doping on the temperature dependences of thermophysical properties of polycrystalline zinc oxide films has been shown.

Critical behavior of Ga1‐xMnxAs

The temperature dependencies of the resistivity, the magnetization, the specific heat and the thermal diffusivity have been conducted in the close vicinity of magnetic phase transition in Ga1‐xMnxAs. Two different types of Ga1‐xMnxAs samples have been investigated. The sample with a Mn concentration of 1.6% shows an insulating behavior and the sample with a Mn concentration of 2.6% is metallic. From the M(T) and M(H) curves by using Arrott plots the Curie temperature and the critical exponents of β, γ, and δ have been determined. The temperature dependencies of the specific heat and thermal diffusivity of Ga1‐xMnxAs samples demonstrated a pronounced λ shaped peak, which indicates an existence of a second‐order phase transition in these samples. The specific heat peak maximum is located near the Curie temperature and therefore, it is attributed to the ferromagnetic‐paramagnetic phase transition. From detailed analysis of the specific heat and the thermal diffusivity data above and below TC, the value of cr...

Bilaterally sensitive photodiode structures in the system gallium arsenide-cadmium sulfide

It has been shown experimentally that in a double‐barrier photodiode structure with a common modulated base region, the spectral characteristics for the cases of cutoff p‐n‐hetero‐ (pGaAs–nCdS) and metal‐semiconductor (m–pGaAs) junctions can have the identical form where the mechanism of formation is determined by the processes occurring in the regions of space charge which are located predominantly in the common (pGaAs) region.

Pressure transducer based on tensosensitive films of bismuth-antimony telluride

A new design of a semiconductor pressure transducer based on tensosensitive films of bismuth–antimony telluride, which provides a temperature compensation for the entire device structure, is proposed. The technical data of the tensometric transducer proposed for measuring the pressure of liquids and gases are presented.