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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.
Magnetic Phase Transitions in Zn1−xMnxO
Kh. T. Igamberdiev,Sh. U. Yuldashev,권영해,강태원,S. A. Chizhik,A. V. Trukhanov,Sh. M. Rakhimova 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.10
Thermal diffusivity measurements have been used to study the magnetic phase transitions in ZnOdoped with Mn. The temperature dependencies of the thermal diffusivity in the wide temperaturerange from 70 to 300 K reveal an inverted-lambda-shaped peak at a temperature of 75 K forZn0.95Mn0.05O doped with nitrogen and additional peaks at 117 K and 122 K for the nitrogen-dopedand the undoped Zn0.95Mn0.05O samples, respectively. The lambda-shaped peak demonstrates theexistence of a second order phase transition in these samples. The thermal diffusivity peak at 75 Kwas attributed to a ferromagnetic-paramagnetic phase transition in the Zn0.95Mn0.05O doped withnitrogen, and the peaks at 117 K and 122 K were attributed to an antiferromagnetic-paramagneticphase transition in the MnO nanoclusters.
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.