Long-range ferromagnetic order in perovskite manganite La0.67Ba0.25Ca0.08Mn(1-x)Ti x O3 (x = 0.00, 0.05 and 0.10).

In this study, we report the effects of Ti on the critical behavior of La0.67Ba0.25Ca0.08MnO3 samples prepared by the flux method. Moreover, the critical exponents ß, γ and δ are estimated through numerous techniques such as the modified Arrott plot, the Kouvel-Fisher method and critical isotherm analysis of the magnetic measurements on record near the Curie temperature. Compared to standard models, the estimated critical exponents are close to the theoretical values of the mean-field model for these samples. In order to estimate the spontaneous magnetization at a given temperature, we used a process based on the analysis, in the mean-field theory, of the magnetic entropy change (-ΔS M) vs. magnetization (M). An excellent agreement was found between the spontaneous magnetization determined from -ΔS M vs. M 2 and the classical extrapolation from the Arrott curves (µ 0 H/M vs. M 2), thus confirming that -ΔS M is a valid approach to estimate the spontaneous magnetization in this system. The accuracy of the critical exponent values was confirmed with the scaling hypothesis. The magnetization curves fall onto one of two sides, below and above T C.

Critical behavior near room temperature in La0.75Ca0.05Na0.20MnO3 sample.

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.

Large magnetocaloric entropy change at room temperature in soft ferromagnetic manganites.

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 R3̄c space groups, respectively. While, the x = 0.20 sample crystallized in the rhombohedral structure with a R3̄c 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.