The electronic properties of single-wall carbon nanotubes (SWNTs) have been studied using dc magnetization and electron spin resonance (ESR). The dc magnetization displays a weak diamagnetic susceptibility of ≈ 10-7 emu/g. ESR measurements reveal a narrow resonance line of low intensity and metallic line shape. The spin susceptibility shows a major Pauli contribution at high temperatures (T>150 K) and an appreciable Curie component at lower temperatures. A marked drop of the spin susceptibility is observed at T<14 K, pointing to the opening of a spin gap at low temperatures. The underlying mechanism is discussed in terms of an electronic instability of the SWNTs or the occurrence of defect-mediated spin magnetism. © 2007 The American Physical Society.

We report an electron-spin-resonance (ESR) study of stoichiometric La1-x Cax Mn O3 for 0

Two polyamine copper(II) compounds of spermine analogues: Cu[H2N(CH2)3NH (CH2)2NH(CH2)3NH2] (ClO4)2 (abbreviated as Spc323) and Cu[H2N(CH2)3NH (CH2)3NH(CH2)3NH2] (ClO4)2 (abbreviated as Spc333) have been synthesized and characterized by spectroscopic methods. The electron paramagnetic resonance (EPR) and photoacoustic spectroscopies have been used for studying CU2+ d-d transitions. The EPR spectra of copper(II) ions in both complexes have displayed a different crystal field symmetry: orthorhombic for Spc323 complex, and axial, with the hyperfine interaction, for Spc333 complex. In the visible region of electromagnetic radiation the photoacoustic absorptions from the d-d electron transitions with different energies and linewidths have been observed. Comparison of the obtained results is made with previous measurements on similar spermine compounds. © 2007 Advanced Study Center Co. Ltd.

The magnetic properties of the site ordered multicomponent vanadate Mg3 Fe4 (V O4) 6 are studied using dc magnetization and electron paramagnetic resonance (EPR) measurements. The static susceptibility shows antiferromagnetic interactions between Fe3+ spins with a Curie-Weiss temperature =-111 (1) K, while a transition to a spin-glass-like state is observed at T≈8.5 K, indicating appreciable spin frustration. EPR measurements corroborate the presence of antiferromagnetically coupled Fe3+ spins from high temperatures, while a distinct change in the temperature variation of the EPR parameters is observed at T<80 K, complying with the mean-field energy scale provided by the Curie-Weiss temperature of the system. The resulting magnetic inhomogeneity that persists despite the absence of cation disorder between magnetic and diamagnetic metal ions is attributed to the presence of small amounts of oxygen deficiency that modifies the connectivity and superexchange coupling between Fe3+ spins and leads to a disordered magnetic ground state. © 2007 American Institute of Physics.

The magnetic and dielectric properties of the Ni2 FeV3 O11-6 compound synthesized using different annealing routes have been studied by means of static magnetization, electron paramagnetic resonance and dielectric spectroscopy. The temperature dependence of the magnetic susceptibility has shown marked singularities due to the coexistence of many kinds of magnetic interactions. Dielectric measurements have shown a second order phase transition to the ferroelectric state at about 200K. Dielectric loss measurements have shown an intense peak at the same temperature with activation energy of about 0.42 eV. All investigated compounds of the M-Fe-V-O (M=Ni, Zn, Mg) system have displayed a slight anomaly of the EPR parameters at about 200K. This anomaly is interpreted as arising from the competition between different magnetic subsystems preventing the formation of a long-range magnetic order. © 2007 Advanced Study Center Co. Ltd.