RESUMEN
Our present study focuses on examining the thermal, structural and luminescent characteristics of sodium barium metaphosphate glasses doped with Sm3+. Glass samples with molar compositions (100 - y)[(50P2O5)-(50-xNa2O)-(xBaO)]-ySm2O3, where x = 20, 25, 30, 35, 40 and y = 0.3 and 1% were first synthesized by conventional melt quenching and later dehydroxylated under a constant N2 flow to ensure final glasses with a very high degree of chemical and optical homogeneity and free of water. Upon the addition of BaO and Sm2O3, refractive index, molar mass, density, glass transition temperature and dilatometric softening temperature exhibited an increase, whereas the coefficient of thermal expansion showed a decrease. The FTIR spectra analysis reveals a network depolymerization that intensifies with rising BaO concentration, ultimately transitioning from a modifier oxide to a glass-forming element, at higher BaO concentrations. All doped samples exhibited prominent absorption bands in the visible (VIS) and near-infrared (NIR) regions, as revealed by the optical absorption spectra. The Na2O modifier demonstrated greater influence on Sm3+ emission compared to BaO, a phenomenon that can explained by the moderation of the local ligand field strength resulting from this substitution. With an increase in Sm2O3 concentration from 0.3 to 1 mol%, the experimental lifetimes of the 4G5/2 level decrease, primarily attributed to the presence of energy transfer mechanisms. A discussion of Judd-Ofelt parameter analysis and glass radiation properties will be presented.
RESUMEN
In this paper, we have studied the critical behavior and the magnetocaloric effect (MCE) simulation for the La0.75Ca0.1Na0.15MnO3 (LCNMO) compound at the second order ferromagnetic-paramagnetic phase transition. The optimized critical exponents, based on the Kouvel-Fisher method, were found to be: ß = 0.48 and γ = 1. These obtained values supposed that the Mean Field Model (MFM) is the proper model to analyze adequately the MCE in the LCNMO sample. The isothermal magnetization M(H, T) and the magnetic entropy change -ΔSM(H, T) curves were successfully simulated using three models, namely the Arrott-Noakes equation (ANE) of state, Landau theory, and MFM. The framework of the MFM allows us to estimate magnetic entropy variation in a wide temperature range within the thermodynamics of the model and without using the usual numerical integration of Maxwell relation.
RESUMEN
The critical behavior of La0.75Ca0.05Na0.20MnO3 was studied at around room temperature via magnetization measurements. From the relative slope, we deduced that the Tricritical Mean-Field model was the most suitable model. The estimated critical exponents were found to be ß = 0.24 ± 0.004, γ = 0.98 ± 0.065 and δ = 5.08 at T C = 300 K. These critical exponents satisfied the Widom scaling relation δ = 1 + γ/ß, implying the reliability of our values. Based on the critical exponents, the magnetization-field-temperature (M-µ 0 H-T) data around T C collapsed into two curves, obeying the single scaling equation with ε = (T - T C)/T C being the reduced temperature. These results suggest short-range interaction in our sample.
RESUMEN
In this paper, La0.75Ca0.25-x Na x MnO3 (x = 0.15 and 0.20) samples were prepared by the flux method. Crystallographic study revealed that the x = 0.15 sample is characterized by the coexistence of a mixture of orthorhombic and rhombohedral structures with Pbnm and R3Ìc space groups, respectively. While, the x = 0.20 sample crystallized in the rhombohedral structure with a R3Ìc space group. Magnetic data, under a magnetic field of 0.05 T, indicated that our samples undergo a ferromagnetic (FM)-paramagnetic (PM) phase transition, on increasing the temperature. The magnetic field dependence of the magnetocaloric properties of La0.75Ca0.25-x Na x MnO3 (x = 0.15 and 0.20) samples, with the second phase transition, was investigated. Near room temperature, the x = 0.20 sample exhibited a large magnetic entropy change with maxima of 6.01 and 3.12 J kg-1 K-1, respectively, under applied magnetic fields of 5 and 2 T. Also, the relative cooling power (RCP) was calculated. According to hysteresis cycles, for our studied samples, at 10 K a typical soft FM behavior with a low coercive field was observed. These results make our samples promising candidates for magnetic refrigerators, magnetic recording, and memory devices.