Enhanced room-temperature magnetoresistance in partially melted La0.67Ca0.33MnO3 manganites

Abstract

We have performed magnetic and transport measurements on La0.67Ca0.33MnO3 polycrystalline and partially melted samples. The magnetization and resistance decrease as sintering temperature is increased. The insulator-to-metal transition temperature is remarkably enhanced in the partially melted sample, enabling its possible applications at room temperature. The microscopic studies in melt samples show an excellent connectivity between grains, suggesting the enhancement of percolative transport by opening new conduction channels and the disappearance of magnetic phase boundary at elevated temperature by the ordering of Mn spins blocked at the grain boundary of sintered samples.

The effect of Ho-doping and Ho-adding on electronic transport and magnetic properties of La0.67Ca0.33MnO3

“…In the r-T curve, the melt-processed LCMO exhibits a sharp T c at B261 K which is enhanced compared with that of sintered LCMO. It was explained due to the opening of new conduction channels blocked at GB with improved grain boundaries for the meltprocessed sample [19,20]. Compared with Ho-free LCMO, T c of Ho-LCM (1 mol% Ho addition to LCMO) is increased B70 K and T c of Ho-doping LCM is decreased B35 K. This kind of variation of T c can be explained reasonably by the results of XRD refinement shown in Fig.…”

“…La 0.67 Ca 0.33 MnO 3 (LCMO); La 0.64 Ho 0.03 Ca 0.33 MnO 3 (Ho-doping LCM) and 1 mol% Ho addition to LCMO (Ho-LCM) samples were prepared by melt processing technique [22]. The samples were fully melt processed at B1600-1620 C and annealed in O 2 .…”

“…The doping changes the structural parameters which directly influences the e g electrons hoping between Mn ions. The connectivity between grains enhances spin polarization between the adjacent grains through perovskite grain boundary (GB) region [19,20], because in ferromagnetic-metal mixture, the negative magnetoresistance (MR) effect originates from the spin-dependent scattering at the boundaries of the non-aligned magnetic grains. However, for bulk ceramic material, nearly 100% spin polarization remains an intriguing problem both for technological and scientific point of view.…”

Low field magnetoresistance of La 0.7 Ca 0.3 MnO 3 ceramics fabricated by fast sintering process

“…For LCMO30 specimen, the extra high temperature may induce partially melted phase during the heating process. The nature of magnetization is only slightly influenced by the grain connectivity in the partial-melt samples [17]. Hence, LCMO30 shows the reduced magnetization.…”

Ultrafast sintering of La–Ca–Mn–O bulk ceramics by thermal plasma assisted heating

“…In order to understand the exotic properties of rare-earth-based CMR manganites considering its exchange interaction and phase separation phenomenon, it is required to process these materials (both thin film and bulk form) under different heating schedules, aiming to exploit the microstructure and grain-boundary-related magnetotransport properties required for CMR applications. In this connection, attempts of our research group in making partial-melt La 0.67 Ca 0.33 MnO 3 (LCMO) CMR manganites, adopting a long-range heating schedule (20 h) at high temperatures, preferably 1620 1C [6,7], may be referred to, which showed enhanced room temperature MR. The microscopic studies carried out by us [6,7] in partial-melt samples exhibit an excellent connectivity between grains, suggesting the enhancement of percolative current transport by opening new conduction channels and disappearance of magnetic phase boundary at elevated temperatures by the ordering of Mn spins blocked at the grain boundary of sintered samples.…”