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Thermal Diffusivity Study of Weak Ferromagnetism in Zn_(1−x)Co_xO
Khusan T. Igamberdiev,Shavkat U. Yuldashev,권영해,강태원,Vasiliy O. Pelenovich,Anatoly G. Shashkov 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.51
Thermal diffusivity measurements have been conducted in order to study the origin of ferromagnetism in Zn_(1−x)Co_xO. Thin films of Zn_(1−x)Co_xO (x = 0.03) were deposited on Si (100) substrates by using ultrasonic spray pyrolysis. Magnetization M(H) measurements at low temperaturs show a hysteresis loop, which indicates the existence of ferromagnetic ordering in Zn<SUB>0.97</SUB>Co<SUB>0.03</SUB>O. However, the magnetic moment per Co ion is much lower than expected. A comparison of M(T) measured at zero-field-cooled (ZFC) and at field-cooled (FC) conditions shows a superparamagnetic-like behavior, and the blocking temperature is about 130 K. The temperature dependence of the thermal diffusivity of Zn_(0.97)Co_(0.03)O shows a pronounced lambda-shaped minimum at 130 K, which indicates the existence of a second-order phase transition at that temperature. The weak ferromagnetism in Zn_(0.97)Co_(0.03)O with a Curie temperature of 130 K is ascribed to an uncompensated magnetic moment at the surface of CoO nanoclusters with radii of about 1 nm.
Study of Ga<SUB>1-x</SUB>Mn<SUB>x</SUB>As Critical Behavior by Using Thermal Diffusivity
Shavkat U. Yuldashev,Khusan T. Igamberdiev,이세준,권영해,강태원,Anatoly G. Shashkov 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.21
The temperature dependence of the thermal diffusivity has been measured in the close vicinity of the magnetic phase transition in Ga_(1−x)Mn_xAs. The thermal diffusivity of Ga_(1−x)Mn_xAs samples demonstrated a pronounced -shaped peak, which indicates the existence of a second-order phase transition in the samples. The thermal diffusivity peak maximum is located near the Curie temperature;therefore, it is attributed to a ferromagnetic-paramagnetic phase transition. Taking into account that the inverse of the thermal diffusivity has the same critical behavior as the specific heat,we determine the critical exponent . The critical behavior of the specific heat of the Ga_(1−x)Mn_xAs samples is well described by the mean-field, including Gaussian fluctuations, model.
Effects of near-surface defects on the optical, electrical and magnetic properties of ZnO films
Yalishev, Vadim Sh.,Yuldashev, Shavkat U.,Igamberdiev, Khusan T.,Kang, Tae Won,Park, Bae Ho Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.10
We studied the optical, electrical and magnetic properties of ZnO films prepared by using a pulsed laser deposition method. Low-temperature photoluminescence (PL) measurements revealed a strong emission line at 3.333 eV. A dependence of this emission intensity on oxygen adsorbed on the surface was observed, indicating a near-surface origin for the emission. The transition at 3.333 eV was attributed to bound exciton, and the observed anomalously small thermal activation energy in comparison with the localization energy could be explained by a modification of the surface state. The observed resistance switching effect and ferromagnetism in the ZnO films were related to the existence of defects responsible for the PL emission at 3.333 eV.
Yalishev, Vadim Sh.,Yuldashev, Shavkat U.,Igamberdiev, Khusan T.,Kang, Tae Won,Park, Bae Ho Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.1
We studied the photoluminescence (PL) spectra in the near-band-edge region of undoped ZnO films as a function of temperature to determine the thermal quenching behavior in the emission intensity. The quenching of the PL intensity was found to change to an increasing intensity with increasing temperature in the temperature region from 40 to 60 K. On the other hand, a reduction of the vacuum in the same temperature region was observed and was attributed to desorption of oxygen molecules from the cryostat finger. Further investigation revealed that the increase in the PL intensity was caused by adsorption of oxygen on the surface of ZnO films resulting in a decrease in the number of non-radiative recombination centers.
Synthesis and Stabilization of Cobalt and Copper Nanoparticles by Using Bombyx Mori Chitosan
Noira R. Vokhidova,Sergei M. Yugay,Sayyora Sh. Rashidova,율다세프,Khusan T. Igamberdiev,Vadim Sh. Yalishev,강태원 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.8
Cobalt and copper nanoparticles (NPs) were prepared by using 2-propanol in the presence of Bombyx mori chitosan to reduce the metals. The structural and the optical measurements show that chitosan molecules prevent the agglomeration and oxidation of the metal nanoparticles. The concentration of chitosan was shown to have a strong influence on the size and the distribution of NPs in a polymeric matrix.