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Beersheba, Israel

Auslender M.,Israel Electric | Shames A.I.,BGU of the Negev | Rozenberg E.,BGU of the Negev | Sominski E.,Bar - Ilan University | And 2 more authors.
Journal of Applied Physics | Year: 2010

The X -band electron paramagnetic resonance in La0.5 Ca0.5 MnO3 was studied. Fitting the measured temperature dependence of the EPR linewidth and intensity to established models were employed to probe the effects of finite-size and nonstoichiometry. Regarding these effects, the complex mixed magnetic ordering inherent in bulk samples was shown to be unstable. The antiferromagnetic (AFM) and charge ordered component is suppressed in nanosamples. But the ferromagnetic (FM) state, appearing in nanograins, 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. In addition, a weak nonstoichiometry which does not affect the crystal structure in bulk induces a strong decrease of the FM component in its magnetic ground state. © 2010 American Institute of Physics. Source


Rozenberg E.,BGU of the Negev | Shames A.I.,BGU of the Negev | Auslender M.,Israel Electric
Nanoscience and Nanotechnology Letters | Year: 2011

The X-band electron paramagnetic (EPR) and ferromagnetic resonance (FMR) measurements in the temperature range 5 K-600 K were used to explore the nanometer size effects on magnetic ordering in hole-and electron-doped compounds, belonging to the prototypical system of doped manganites-La 1-xCaxMnO3 (x = 0.1, 0.3, 0.5 and 0.6). To this end, the modelflttings of the temperature dependences of doubly integrated intensity and linewidth of EPR signal, as well as comparative analysis of both FMR data and the known results of neutron diffraction and magnetic measurements were performed. It appears that strongestfinite-size effects are observed for lowhole-doped x = 0.1 nano-crystals due to suppression of chemical/structural disorder characteristic for bulk. The x = 0.3 and 0.5 series demonstrate well pronounced effect of core/shell spin con-.guration on paramagnetic spin correlations and spin dynamics, as well as on low temperature magnetic ordering. The electron-doped x = 0.6 nano-crystals differ strongly from all other considered nano-samples-the antiferromagnetic charge ordered ground state was found to be stable in this case due to, supposedly, the local nature of double exchange coupling and resulting localization of carriers. Source


Rozenberg E.,BGU of the Negev | Auslender M.,Israel Electric | Felner I.,Hebrew University of Jerusalem | Shames A.I.,BGU of the Negev | And 2 more authors.
IEEE Transactions on Magnetics | Year: 2010

Magnetic and electron paramagnetic resonance measurements were employed to probe magnetic interactions in the single crystal and ceramic of La 0.7Ca0.3MnO3 manganite in the vicinity and above their paramagnetic-ferromagnetic phase transition. It is shown that strong differences in the Curie point values and in the temperature dependences of inverse susceptibilities are observed in spite of the same structure and cation composition of both samples. We suggest that the difference between lattice effects in these samples, induced by their different chemical disorder, proves a more realistic description of experimental data than so-called Griffiths singularity. © 2006 IEEE. Source

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