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Rozenberg, E.,Tsindlekht, M.I.,Felner, I.,Sominski, E.,Gedanken, A.,Mukovskii, Ya.M.,Cheol Eui Lee IEEE 2009 IEEE transactions on magnetics Vol.45 No.6
<P>AC and dc magnetic measurements in temperature interval 5-350 K and at external magnetic field H les 5 T were employed to probe the finite-size and nonstoichiometry effects on magnetic ordering of La<SUB>0.5</SUB>Ca<SUB>0.5</SUB>MnO<SUB>3</SUB> half-doped manganite compound. It is shown that the complex mixed magnetic ordering in bulk samples appears to be unstable regarding the both effects. The strongest one is the size effect, suppressing the mixed order and inducing the ferromagnetic-like one, which is characteristic also for other half-doped manganites. The small variations in cation composition (nonstoichiometry), which don't influence the crystal structure, lead to strong perturbations in the mixed magnetic ordering of the bulk. The results obtained are discussed in the terms of pronounced competition of spin, charge and lattice degrees of freedom, characteristic for doped manganites.</P>
Rozenberg, E.,Shames, A. I.,Jung, G.,Mukovskii, Ya. M.,Sominski, E.,Gedanken, A.,Lee, Cheol Eui Wiley - VCH Verlag GmbH & Co. KGaA 2007 Physica status solidi. B Vol. No.
<P>Electron spin resonance was studied on three (two bulk and one nanometer sized) samples of the same La<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB> manganite compound aiming to compare their magnetic homogeneities. The results obtained show that both ceramic and single crystalline bulk samples are less homogeneous than nano-crystalline one. Except for higher homogeneity, the nano sample demonstrates also a weaker magnetic anisotropy. As a result, well pronounced coexistence of different magnetic phases (coexistence of ferromagnetic and paramagnetic resonance signals) is observed in bulk samples, while it is absent in nano. It is suggested that such strong difference is directly connected to the difference in structural state of the samples. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Nanometric Size Effect on Magnetic Ordering in Half-doped La0.5 Ca0.5 MnO3 Manganite: EPR Probing
M. Auslender,E. Rozenberg,A. I. Shames,D. Mogilyansky,E. Sominski,A. Gedanken,이철의 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61
Measurements of the X-band electron paramagnetic resonance and the model fittings of the linewidth and intensity versus temperature dependences were employed to probe the finite-size effect on the magnetic ordering in half-doped La0.5 Ca0.5 MnO3 manganite. It is shown that complex mixed magnetic ordering in bulk samples, comprised of the antiferromagnetic and the charge-ordered (AFM/CO) component, together with the ferromagnetic one, appear to be unstable regarding this effect; the AFM/CO phase is suppressed in nano-samples, which agrees with the data of magnetic measurements. In addition, we have managed to show that the FM state, appearing in nano-grains, is frustrated due to (i) an AFM-like core-shell interaction and (ii) a strong spin disorder at the surfaces and core-shell transition layers.
이규원,이철의,A. Gedanken,E. Sominski,Yu. Koltypin 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.6
We have studied the magnetic and the electric properties of La_(0.8)Sr_(0.2)MnO_3 (LSMO)nanoparticle-decorated carbon nanotubes (CNTs). The magnetic susceptibility showed a paramagnetic - superparamagnetic phase transition at TSP » 200 K with a blocking temperature of T_B ∼ 120 K, which can be attributed to the LSMO nanoparticles. At T_(SP), the charge transport taking place through the CNTs network showed a metal-insulator transition (MIT) characteristic of the LSMO nanoparticles, indicating a concomitant MIT in the CNTs triggered by the LSMO nanoparticles. In the metallic phase, the charge transport appears to be dominated by a 2D weak localization effect, which at temperatures below T_B was seen to be somewhat suppressed by the internal field. At temperatures below 50 K, a Kondo effect dominates the electric and the magnetic properties.
Electron magnetic resonance (EMR) in sonochemically prepared doped nano-manganites?
A.I. Shames,E. Rozenberg,G. Gorodetsky,I. Felner,E. Sominski,G. Pang,A. Gedanken 한국물리학회 2007 Current Applied Physics Vol.7 No.1
X-band electron magnetic resonance method was explored for study of sonochemically prepared nano-powders of La-based dopedmanganites: La0.7Sr0.3MnO 3 and La0.9Ca0.1MnO 3 at 1156 T6 600 K temperature interval, including main characteristic points of itsmagnetic transitions. The data obtained were compared with those for crushed bulk single crystals of the same compositions. It is shownthat nano-powder of La0.7Sr0.3MnO 3 has the same ferromagnetic ordering as its bulk counterpart, being more homogeneous and lessanisotropic. While, nano-powder of La0.9Ca0.1MnO 3 shows two distinct ferromagnetic phases in a marked contrast to the bulk sample,where complex magnetic structure comprising canted antiferromagnetic matrix and ferromagnetic clusters is observed. To explain theobserved phenomena, the crucial role of nano-scale grain size and its interplay with spin and charge degrees of freedom in consideredsystems are discussed.