Room-temperature magnetoresistive and magnetocaloric effect in La1−xBaxMnO3 compounds: Role of Griffiths phase with ferromagnetic metal cluster above Curie temperature

Abstract

The evolution of the Griffiths phase (GP) with a ferromagnetic metal (FMM) cluster above the Curie temperature (TC) and its effect on the magnetic properties, electrical transport, magnetoresistance (MR), and magnetocaloric effect (MCE) is studied comprehensively, using bulk compounds of La1−xBaxMnO3 (0.15 ≤ x ≤ 0.25) with different lattice distortions but with the same structural symmetry and space group. These La1−xBaxMnO3 samples show ferromagnetic transition at TC increasing from 229 K for x = 0.15–300 K for x = 0.25, in addition to the presence of GP with FMM clusters in the paramagnetic (PM) region, which have been confirmed by the combination of magnetization (susceptibility) measurements, the GP theory, and electron paramagnetic resonance technology. With increasing the Ba2+ ion doping, GP temperature (TG) and TC of La1−xBaxMnO3 are increased, and the GP regime is strengthened. The GP ratio in the PM region reached 27.7% for the sample with x = 0.20. The resistivity decreases and the FMM phase increases with increasing x from 0.15 to 0.25, which can be explained by the decrease in the bandgap (Eg) and the enhancement of the double-exchange effect. Remarkably, large room-temperature MR (∼44.7%) can be observed in the sample with x = 0.25 under 60 kOe, which is related to the presence of the GP regime. Furthermore, the MCE is also affected by the GP regime, and it is deduced that the magnetic transition is of second order. The value of magnetic entropy change (|ΔSM|) reaches 3.04 J/kg K near room temperature for the sample with x = 0.25 under 50 kOe. This value is associated with a relative cooling power (RCP) of 248.1 J/kg. For the sample with x = 0.15, the value of RCP reaches 307.6 J/kg under 50 kOe. The discovery of the MR and MCE near room temperature is of great significance from the practical application of perovskite manganites in magnetic sensors and magnetic refrigerants.

Investigating the Correlation between the Microstructure and Electrical Properties of FeSbO4 Ceramics

“…The higher interconnection grains number with clusters of small grains forming densely packed aggregates (2.55 ± 1.25) μm can also justify this significant porosity, as observed in the SEM image ( Figure 2 d). Thus, we can see that the initial powder particle size distribution significantly affects the density and microstructure of the ceramics, as reported in other oxides [ 25 , 26 , 27 ]. Herein, the larger particle sizes for the P-1000 powder resulted in ceramics with higher porosities than those produced using the P-900 powder with smaller particles.…”

“…From the adjustment of Equation (13) to the impedance spectroscopy experimental data, it was possible to determine the R and C values for the grain and grain boundary regions. To compare the electrical parameters, the resistances and capacitances were normalized by the geometric parameters (𝑑∙A −1 ) of the sample and to obtain the activation energy of the grain and grain boundary regions through the Arrhenius plot [ 27 ]; see Figure 9 . To obtain the grain activation, and grain boundary energies, the Arrhenius equation for electrical conductivity was used, given by Equation (14): where is the electrical conductivity associated with the charge carriers available for conduction in , is the activation energy required for the carrier to move in the crystal lattice of the ceramic in , is the Boltzmann constant in , and is the temperature in .…”

Magnetostructural Transition and Magnetocaloric Effect with Negligible Magnetic Hysteresis in MnCoGe1.02−xGax Alloys

“…Figure 8 exhibits the M 2 -µ 0 H/M curve (Arrott cure) of the MnCoGeGa 0.02 alloy based on Figure 7a, where the temperature range is 250-340 K. According to some related reports [20,21], the presence of a negative slope or S shape in the Arrott curve verifies a first-order phase transition. As shown in Figure 8, the S-shaped curve is observed near structural transition, implying that the first-order magnetostructural transition occurs.…”

Application of Grazing-Incidence X-ray Methods to Study Terrace-Stepped SiC Surface for Graphene Growth

“…It should be noted that numerous recent works applied AFM data in conjunction with X-ray experiments to characterize interfaces, for example [ 35 , 36 ]. However, in these publications interfacial roughness has been only considered in terms of root-mean-square (rms) roughness height σ , which has several downsides.…”