Magnetotransport properties of a single grain boundary in a bulk La–Ca–Mn–O material

Abstract

Besides the ''intrinsic'' colossal magnetoresistance effect observed in single crystals, the polycrystalline manganate compounds also exhibit an ''extrinsic'' magnetoresistance related to the presence of grain boundaries. We report electrical transport and magnetic measurements carried out on a bigrain sample extracted from a floating zone method-grown rod of calcium doped lanthanum manganate. Electrical resistance was measured both within a grain and across the grain boundary, between 20 and 300 K and from 0 to 8 T. Magnetoresistance values up to 99% are reached within the grain. The temperature dependence of the resistance across the grain boundary displays a ''foot-like'' feature towards the bottom of the transition. Low field and high field magnetoresistance effects are examined. We compare our results for a ''bulk'' grain boundary to those obtained by other authors for bicrystal thin films and bulk polycrystalline materials.

Extrinsic inhomogeneity effects in magnetic, transport and magnetoresistive properties of () crystal prepared by the floating-zone method

“…2 and 3) and a far less pronounced one at T pin ≈ 190 K. Additionally, ρ(T ) exhibits two shallow minima, one is situated at T Above T c , the sample is a PM non-metal with an activated temperature dependence of resistivity, following ρ(T ) ∝ exp(E a /T ). The activation energy E a is found to be equal to 0.09 eV in agreement with that (about 0.1 eV) reported by other authors for single crystal and ceramic samples of La 1−x Ca x MnO 3 (x ≈ 0.33) [17,24,25,30]. It is known [1,2,3] that the conductivity of Camanganites increases enormously at the transition to the FM state.…”

“…The value of ρ(T p )/ρ(0) is about 200 for the sample studied. This is a high value, comparable with that of single crystals and epitaxial films of the best quality [2,24,25,30,31,32]. For ceramic samples, prepared by the solid-state reaction method, the ratio ρ(T p )/ρ(0) is usually far less (see Refs.…”

“…For this reason, CMR is maximal near T c and goes to nearly zero value for T ≪ T c . This behavior is unique to bulk or film manganites of rather good crystal perfection [30,33]. The presence of extrinsic inhomogeneities (such as grain boundaries) gives rise to an extrinsic MR effect.…”

“…It is well known that samples prepared by the floating-zone method generally have a much sharper resistive transition on going from the PM to FM state than is observed for manganite films (compare data in Refs. [2,24,25,30,31,32]). This is so indeed in the sample studied which has an extremely sharp resistive transition near T c (Fig.…”

Structural, Thermal, Magnetic, and Transport Properties of (La2/3Ca1/3)(Mn1-xSnx)O3-δCompounds

“…Such resistance changes observed near T C are viewed as canonical for DE systems [21] and are intrinsic, bulk properties. Some authors call this colossal magnetoresistance effect observed in good-quality single crystals the "intrinsic" as opposed to the "extrinsic" magnetoresistance exhibited by the polycrystalline manganites, which is related to the presence of grain boundaries (GB) [22]. The "extrinsic" magnetoresistive effects are known to be due to spin-dependent scattering or tunnelling processes at the grain boundaries, inhomogeneities, microcracks and macroscopic defects.…”