Vol 50, No 12 (2019)

Zinc substitution effects on the magnetic ordering of nanosized Nd_0.65Ca_0.35MnO₃ particles prepared by sol–gel method have been investigated by electron magnetic resonance (EMR) technique complimented by magnetization measurements. Bulk Nd_0.65Ca_0.35 MnO₃ exhibits a charge ordering transition at 240 K and an antiferromagnetic transition at 150 K followed by a transition to a ferromagnetic (FM) phase below 50 K. In contrast, the nano Nd_0.65Ca_0.35MnO₃ exhibits only a single transition from paramagnetic to ferromagnetic phase at 102 K which supports the general phenomenon of vanishing phase complexities in nano materials. In this paper, we discuss the effect of 10% and 30% zinc doping on the nano sized Nd_0.65Ca_0.35Mn_1–x Zn_xO₃. Magnetization and EMR studies confirm the existence of ferromagnetism in all the samples which weakens with increasing doping of zinc. Though magnetization measurements do not show the charge order fluctuations and short range antiferromagnetic (AFM) order in the zinc-doped samples, EMR measurements evidence it. Electron magnetic resonance line width increases with zinc doping over a wide range of temperature due to the destruction of motional narrowing.

The filter diagonalization method (FDM) was implemented and used instead of fast Fourier transform (FFT) to obtain the nuclear magnetic resonance (NMR) spectra from the free induction decay (FID) signals. The areas obtained by the FDM, from selected absorption lines, were used as input for a multidimensional method of data analysis. This procedure was applied in a NMR-based metabolomics investigation. In FDM, instead of spectra, the absorption peaks’ specification, such as central frequency, line width, amplitude and relative phases, are estimated and the spectra are built using this information. Therefore, one can select the lines by width and intensity to exclude the broad lines such as baseline, solvent line and albumin peak. Also lines with small amplitude such as noise can be excluded from the spectra. Moreover, the spectra do not suffer from aliasing or baseline problems. These characteristics are fundamental in the metabolomics investigations. To show the superiority of our method over the standard FFT to obtain the spectra, we reconstructed the spectra from simulated FID by both methods. As an example, this new approach is used to analyze the non-small cell lung cancer A549 exposed to different treatments and principal component analysis is used to compare the performance of both methods.

The exchange interaction in two isostructural compounds [M₂Dy₂ (μ₃–OH)₂(L)₂(O₂CPh–Me–p)₆] (M = Al, Cr) is studied by electron paramagnetic resonance (EPR). Studies have been performed on polycrystalline samples in different frequency ranges. The features of the shape of the spectra of clusters containing dysprosium ions are analyzed and experimental spectra are described using calculated spectra for tetranuclear clusters. The value J_zz = − 0.86 cm⁻¹ of the spin–spin interaction of the Ising form J_zzS_1zS_2z between dysprosium ions in the Al₂Dy₂ cluster, which exhibits single-molecule magnet properties, was experimentally determined. The study of the heteronuclear Cr₂Dy₂ cluster has demonstrated a number of features of the EPR spectra due to the Cr–Dy interaction. It is shown that this interaction has a predominantly Ising form with the parameter J_CrDyzz = − 1 cm⁻¹. However, the Cr–Dy pair fragment does not have a center of symmetry, and this suggests the presence of an antisymmetric term in the spin–spin interaction tensor, the manifestation of which is observed in the X-band EPR spectrum.

The ⁵¹V and ²⁵Mg nuclear magnetic resonance (NMR) spectra have been obtained and magnetic susceptibility has been measured in polycrystalline Mg₃V₂O₈. The analysis of ⁵¹V NMR spectra has shown that the line shift, δ(⁵¹V) = − 555 ppm, does not depend on temperature. It has been established that vanadium ions V⁵⁺ have a zero magnetic moment in this structure. The ²⁵Mg NMR spectrum consists of two lines corresponding to two crystallographically nonequivalent positions of magnesium ions in the Kagome structure: Mg(1) are « spine » and Mg(2) are « cross tie » . Quadrupole frequencies and asymmetry parameters of ²⁵Mg and ⁵¹V NMR spectra have been determined. The magnetic susceptibility is turn out to be zero (within the error) and remains constant over at a whole temperature range.