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Irreversible field-induced magnetic phase transitions and properties of Ho<sub>3</sub>Co
Baranov, N V,Goto, T,Hilscher, G,Markin, P E,Michor, H,Mushnikov, N V,Park, J-G,Yermakov, A A IOP Pub 2005 Journal of physics, an Institute of Physics journa Vol.17 No.21
<P>The results of magnetic susceptibility, magnetization, electrical resistivity and specific heat measurements performed on Ho<SUB>3</SUB>Co single crystals show that this compound exhibits two different antiferromagnetic structures: AF<SUB>II</SUB> at 8 K<<I>T</I>< 22 K and AF<SUB>I</SUB> below <I>T</I><SUB>t</SUB>≈8 K. Below the Néel temperature <I>T</I><SUB>N</SUB> = 22 K the application of a magnetic field along the main crystallographic directions induces magnetic phase transitions which are accompanied by giant magnetoresistance. At <I>T</I><<I>T</I><SUB>t</SUB> the field-induced phase transitions along the <B><I>c</I></B>- and <B><I>b</I></B>-axes are found to be irreversible, and a small ferromagnetic component is observed along the <B><I>a</I></B>-axis. These peculiarities are associated with the non-Kramers character of the Ho ion and with the presence of a complex incommensurate magnetic structure of Ho<SUB>3</SUB>Co below <I>T</I><SUB>N</SUB>. The temperature coefficient of the electrical resistivity for Ho<SUB>3</SUB>Co above <I>T</I><SUB>N</SUB> over a wide temperature range is found to differ from that observed for other R<SUB>3</SUB>Co compounds. Such a behaviour is attributed to the presence of an additional contribution to the conduction electron scattering by spin fluctuations induced by f–d exchange in the itinerant d-electron subsystem. The value of this extra contribution and its temperature range is suggested to depend on the spin value of the R ion. The excess of the effective magnetic moment per R ion, which is observed in Ho<SUB>3</SUB>Co and in other R<SUB>3</SUB>M type compounds, is also attributed to spin fluctuations induced by f–d exchange.</P>
Spatially-resolved Study of the Luminescence from ZnO/MgO Core-shell Nanocrystal Structures
파닌,Andrey Baranov,Olesya Kapitanova,강태원 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.3
The luminescent properties of core-shell nanocrystal structures were investigated with high spatial resolution. The composites consisting of ZnO/MgO core/shell nanoheteroparticles showed an increase in the relative intensity of the green luminescence after annealing while a suppression of green luminescence from samples of ZnO tetrapods in a MgO nanoparticle matrix was observed. Combined spatially-resolved combined through-the-lens-detector (TLD) and cathodoluminescence (CL) measurements revealed that the depletion of electrons in the ZnO nanocrystals could lead to a suppression of the luminescence.
Spatially-Resolved Study of Magnetic Properties of Mn-Doped ZnO Quantum Wires
Gennady Panin,Andrey Baranov,Hyun Jeong Kim,Seung Ki Min,강태원 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.6
ZnO nanowires prepared by thermal growth following direct chemical synthesis and doped by Mn and by Mn and Sn impurities were investigated. The nanowires show a single crystal structure and a strong blue shift of the near band edge luminescence, which is attributed to the quantum confinement effect. The magnetic susceptibility of the quantum wires as a function of temperature demonstrated a Curie-Weiss behavior. Hysteresis with a coercive field $<$200 Oe was clearly observed in the magnetization versus field curves at 300 K. Increasing the Mn concentration by Mn and Sn co-doping significantly increased the magnetic hysteresis and the ferromagnetic behavior of the nanowires. Magnetic force microscopy measurements with high spatial resolution revealed a magnetic domain structure in the individual wires. The magnetic domains align perpendicular to the surface and can be controlled by using an external magnetic field.
Luminescent Properties of ZnO/MgO Nanocrystal/Polymer Composite Structure
Gennady N. Panin,Andrey N. Baranov,Irina A. Khotina,Tae W. Kang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
We report on cathodoluminescence (CL) studies of the composite nanostructure obtained by spin coating of a mixture of chemically-deposited ZnO/MgO nanocrystals and a solution processable polymer (PDPV) on a Si substrate with patterned gold electrodes. The effect of an electric field on the CL of the nanostructure was studied at various bias voltages on the electrodes. A positive voltage suppressed the blue-green emission and shifted the emission maximum to the red region. The emission maximum returned to the blue-green region after the eld had been turned off. A model of the electric-field-induced color switching in the ZnO/polymer-based nanostructure is proposed. The bias-voltage-induced interface band bending and the deactivation of the radiative centers, in particular, singly-ionized oxygen vacancies in ZnO nanocrystals, are suggested to govern the relative changes of the blue-green-red emissions. We report on cathodoluminescence (CL) studies of the composite nanostructure obtained by spin coating of a mixture of chemically-deposited ZnO/MgO nanocrystals and a solution processable polymer (PDPV) on a Si substrate with patterned gold electrodes. The effect of an electric field on the CL of the nanostructure was studied at various bias voltages on the electrodes. A positive voltage suppressed the blue-green emission and shifted the emission maximum to the red region. The emission maximum returned to the blue-green region after the eld had been turned off. A model of the electric-field-induced color switching in the ZnO/polymer-based nanostructure is proposed. The bias-voltage-induced interface band bending and the deactivation of the radiative centers, in particular, singly-ionized oxygen vacancies in ZnO nanocrystals, are suggested to govern the relative changes of the blue-green-red emissions.
Synthesis and Properties of Graphene Oxide/Graphene Nanostructures
O. O. Kapitanova,파닌,A. N. Baranov,강태원 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10
We report preparation of graphene oxide (GO)/graphene (G) nanostructures and their structural, optical and electrical properties. GO was synthesized through oxidation of graphite by using the modified Hummer’s method, in which a long oxidation time was combined with a highly effective method for purifying the reaction products. The obtained GO was partially reduced (r-GO) by adding ascorbic acid and thermal annealing. An electrical reduction/oxidation process in r-GO under an electric field was used to form and control the GO/G nanostructures and the potential barrier at the interface. After the treatment, the ratio of the intensity of peak G (1578 cm−1) to that of peak D (1357 cm−1) in Raman spectra of the samples is increased, which is attributed to an increase in the ratio between the sp2 and sp3 regions. The electrical and the luminescence characteristics of the GO/G nanostructures were investigated.
Giant Magnetoresistance and Field-induced Phase Transitions in Tb7Rh3 Single Crystal
Takanori Tsutaoka,Koji Shimomura,Nikolai V. Baranov,Alexey V. Proshkin,Evgeny G. Gerasimov,Pavel B. Terentev 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
High-field magnetization and magnetoresistance measurements have been performed to investigatethe field-induced magnetic phase transitions in Tb7Rh3 single crystals. Metamagnetic transitionswere observed along the a-, b- and c-axes of the hexagonal crystal lattice in the three magneticstates at temperatures below the N´eel temperature TN = 91 K; magnetic field H - temperatureT phase diagrams were constructed for b- and c- axes. At temperatures below TN, the magneticstructure transformations under application of a magnetic field along the b-axis are observed to beaccompanied by the giant magnetoresistance effect (|Δρ/ρ| up to 65%). Magnetization curves measuredat temperatures above TN show inflection points, which may be indicative of phase transitionswithin regions with an antiferromagnetic short-range order persisting in a paramagnetic matrix.
Anisotropic absorption of CdSe/ZnS quantum rods embedded in polymer film
Mukhina, Maria V.,Maslov, Vladimir G.,Baranov, Alexander V.,Artemyev, Mikhail V.,Fedorov, Anatoly V. Techno-Press 2013 Advances in nano research Vol.1 No.3
An approach to achieving of spatially homogeneous, ordered ensemble of semiconductor quantum rods in polymer film of polyvinyl butyral is reported. The CdSe/ZnS quantum rods are embedded to the polymer film. Obtained film is stretched up to four times to its initial length. A concentration of quantum rods in the samples is around $2{\times}10^{-5}$ M. The absorption spectra, obtained in the light with orthogonal polarization, confirm the occurrence of spatial ordering in a quantum rod ensemble. Anisotropy of the optical properties in the ordered quantum rod ensemble is examined. The presented method can be used as a low-cost solution for preparing the nanostructured materials with anisotropic properties and high concentration of nanocrystals.
Luminescence from ZnO/MgO nanoparticle structures prepared by solution techniques
G.N.Panin,A.N.Baranov,오영제,강태원 한국물리학회 2004 Current Applied Physics Vol.4 No.6
The optical and structural properties of mixed ZnO/MgO particles prepared by solution techniques are investigated by thecathodoluminescence and electron microscopy techniques. The samples annealed at 4001000.C show well crystalline wurtzitestructure of the ZnO (MgZnO) particles with the size in range of 10100 nm. Annealing at high temperatures (>700.C) leads to Mgdiusion in ZnO and MgxZn1. xO alloy formation. The blue shifts of the near-band-edge emission as a result of the alloy band gapwidening and quantum connement eect for the small size particles are demonstrated.