Influences of the first-to-second order magnetic phase transformation on the transport properties of La0.7Ca0.3−xBaxMnO3 compounds

Abstract

We studied the influence of the magnetic phase transition on the transport properties of La0.7Ca0.3−xBaxMnO3 compounds with x = 0.05, 0.075, and 0.10. Our experimental results demonstrated the ferromagnetic-paramagnetic and metal-insulator transitions taking place at temperatures TC = 265–300 K and TMI = 280–310 K, respectively, which increase with increasing Ba-doping content. While the x = 0.05 sample undergoes a first-order magnetic phase transition (FOMT), x = 0.10 undergoes a second-order magnetic phase transition (SOMT). The other sample with x = 0.075 is considered as a threshold concentration of the FOMT-SOMT transformation. Further, ρ(T) data in different temperature regions were fitted to different models. The activation energy Ep and density of states at the Fermi level N(EF) were accordingly determined. Notably, N(EF) increases while Ep decreases in the case of applying an external field. We also have found that N(EF) increases when materials transfer from the FOMT to the SOMT, which becomes smallest for the sample having the coexistence of the FOMT and SOMT (i.e., x = 0.075).

Effect of Ba substitution on structural, electrical and thermal properties of La0.65Ca0.35−Ba MnO3 (0 ⩽x⩽ 0.25) manganites

“…These compounds have a disadvantage that their Curie temperatures, T C ($270 K) are well below room temperature. However, partial substitution of Ca by larger sized ions like Sr, Ba and Pb could lead to an increase in T C and an enhancement in MCEs is seen in these compounds [15][16][17][18][19][20].…”

Magnetocaloric Effect in La_0.7Ca_0.25Ba_0.05MnO₃ Nanocrystals Exhibiting the Crossover of First- and Second-Order Magnetic Phase Transformation

“…1(b)(d)), whereas the LCBMO bulk sample undergoes a FOPT. 5) In addition, Franco and Conde 17) suggested that the overlap of all the ¦S m (T ) curves into a unique curve is an additional confirmation of the general validity of the treatment in SOPT materials. From these reasons, clearly, the samples with D = 3957 nm are SOPT materials, while the sample with D = 79 nm is located in between the FOPT and SOPT materials (i.e., the crossover of the first-to-secondorder phase transformation).…”

“…These values are slightly lower than T C obtained for the LCBMO bulk/asprepared sample (³265 K). 5) Clearly, the D reduction did not change the T C significantly, but broadened the FM-PM phase transition region. The phase-transition width determined from the full-width-at-half maximum of the dM/dT versus T curve increases from 12 to 17 K with decreasing D from 79 to 39 nm, respectively.…”

“…First, a polycrystalline LCBMO bulk sample with the FOMT was prepared by solid-state reaction; detailed descriptions can be found elsewhere. 5) After that, the LCBMO bulk sample was ground in powder, and divided into parts of 2 g for the mechanical milling with milling times t m = 10, 20 and 30 minutes, used the zirconia-grinding medium supplied by SPEX-SamplePrep. The ball-to-powder mass ratio was maintained at 4.7.…”

“…This character makes SOPT materials more useful for magnetic refrigeration applications. For La 0.7 Ca 0.3 MnO 3 , modifying its FOPT to the SOPT is known as the rounding, which can be carried out by doping 4,5) and reducing crystalline size 2,6,7) or dimensionality in the system. 8) Depending on dopant types, doping content, and crystalline size, rounding results would be different.…”