An X- and Q-band Gd3+ EPR study of a single crystal of EuAlO3: EPR linewidth variation with temperature and low-symmetry effects

Detailed electron paramagnetic resonance (EPR) studies on a single crystal of Gd3+-doped Van-Vleck compound EuAlO3, potentially a phosphorescent/luminescent/laser material, with the Gd3+ ion substituting for the Eu3+ ion, were carried out at X-band (9.2 GHz) over the 77–400 K temperature range. They provide new physical results on magnetic properties of the Eu3+ ion in a low symmetry environment. The asymmetry exhibited by the variation of the Gd3+ EPR line positions for the orientations of the external magnetic field about the Z and X magnetic axes in the ZX plane was ascribed to the existence of low, monoclinic, site symmetry, as revealed by the significant values of the spin-Hamiltonian (SH) parameters and , estimated by fitting all the observed EPR line positions at room temperature for the orientation of the magnetic field in the magnetic ZX plane using a least-square fitting procedure. The temperature dependence of the Gd3+ EPR linewidth is interpreted to be due to the “life-time” broadening, caused by dynamical exchange and dipolar interactions between the impurity Gd3+ ions and the host Eu3+ ions

EPR and magnetization studies of the manganites La0.7-xEuxSr0.3MnO3 (x = 0.4, 0.5, 0.6, 0.7) and La0.3Nd0.4Sr0.3MnO3 at different temperatures: Conductivity due to hopping of small polarons

Four Eu-Sr manganites, La0.7-xEuxSr0.3MnO3; x = 0.4, 0.5, 0.6, 0.7, and one Nd-Sr manganite Nd0.4La0.3Sr0.3MnO3, were studied by EPR (electron paramagnetic resonance) at 9.6 GHz at temperatures in the range 175 – 400 K. These studies were further supplemented by magnetization measurements. The positions and widths of the EPR lines of all the Eu-Sr manganite samples, containing Eu3+ ions, changed with temperature in a similar manner. The EPR data showed that these Eu-Sr manganites are ferromagnetic, whose magnetic transition temperature from the ferromagnetic to the paramagnetic state (TC) decreased gradually as the Eu content (x) increased, specifically from TC ~ 111 K (x = 0.5) to TC ~ 57 K (x = 0.7). Furthermore, in these samples the FMR (ferromagnetic resonance) lines appeared significantly above the respective TC, specifically, at 290 K (x = 0.4), 280 K (x = 0.5), 250 K (x = 0.6), together with the EPR lines. As for the sample with x = 0.7 no FMR lines were observed in the temperature range investigated here. The temperature dependence of the EPR linewidth is found to be linear in the various La0.7-xEuxSr0.3MnO3 samples, caused by the presence of conductivity due to small-polaron hopping The peak-to-peak first-derivative EPR linewidths, ΔBpp, of these Eu-doped samples fitted well above the temperature, at which the minimum of ΔBpp occurs, to the expression: ΔBpp (T) = ΔBpp,min + [Formula presented]exp(-Ea/kBT), with the values of the activation energies being Ea = 0.20 eV, 0.17 eV, 0.11 eV, 0.09 eV for x = 0.4, 0.5, 0.6, 0.7, respectively. On the other hand, for the Nd-doped sample, the ΔBpp in Nd0.4La0.3Sr0.3MnO3 decreased monotonically with temperature above TC in accordance with the Curie-Weiss law as ΔBpp (T) = ΔBpp,0 + C/(T-TC). The magnetization measurements were exploited to determine TC for the various samples. The results agreed with those determined by the EPR measurements presented here. In addition, the magnetization data was analyzed to obtain the values of the critical exponents in the phase transition from the paramagnetic to the ferromagnetic state. The critical exponents, as determined for the La0.7-xEuxSr0.3MnO3 sample with x = 0.5, are β = 0.24 ± 0.02, γ = 1.10 ± 0.5, δ = 5.58

Phase Composition and Magnetic Properties of Nanoparticles with Magnetite–Maghemite Structure

Precipitation of nanopowders with mixed magnetite–maghemite composition was carried out under different conditions and with different separation techniques. The exact character of interactions of different iron oxide phases in the nanopowder was the main object of interest. The obtained nanopowders have spherical particles about 10–20 nm in size. Electron paramagnetic resonance (EPR) study showed that iron ions incorporate fully into magnetite and maghemite structures. The shape of the EPR line points out that single homogenous solid solutions were formed during synthesis. In the studied solid solutions, different ratios of vacancies and Fe2+/Fe3+ ratios were observed but in spite of different synthesis techniques in both cases, there were no additional diamagnetic structural phases presented