Low-temperature resistivity minima in single-crystalline and ceramic La0.8Sr0.2MnO3: Mesoscopic transport and intergranular tunneling

Abstract

A slight minimum in the zero-field resistivity of a single crystalline La0.8Sr0.2MnO3 and shallow one for ceramic La0.8Sr0.2MnO3 samples were observed at T∼4 K and at T∼25–30 K, respectively. The minimum for the ceramic shifts towards lower temperatures, flattens with increasing magnetic fields (H), and vanishes at some critical H. The above effects are accompanied by an appreciable negative magnetoresistance (MR). On the other hand, the minimum for the single-crystalline sample is almost field independent and the MR in the relevant temperature range is very small. Two different mechanisms were found to account for the results observed in the single crystal and the polycrystalline samples: (i) mesoscopic corrections to the bulk resistivity that include Coulomb interaction and weak localization and (ii) intergranular tunneling. The resistivity of the large-grain ceramic sample comprises both types of behavior. The minimum of the bulk contribution becomes clearly seen under H, which suppresses the ceramic-type minimum.

Synthesis and physical properties of arc melted NiMnSb

“…Note that such a power law for the resistivity has been observed also in manganites. 18,19 Auslender et al 18 associated the T…”

Comment on Low-temperature transport properties of non-stoichiometric La0.95 xSrxMnO3

“…(v) This LT minimum of ρ ρ ρ ρ in LSMO polycrystalline sample, as well as slight H-independent upturn of resistivity observed in single crystal of LSMO at liquid helium temperatures were attributed to bulk-like LT conductivity governed by QCC [7].…”

“…(iii) It was shown in [6] and tested additionally in [7] that above minimum phenomenon [6]. But notable differences are observed in LT conductivity for relatively "poor" LPMO and "good" LSMO ceramics (mean grain size is by order of magnitude smaller and residual ρ is by two orders of magnitude higher in former sample comparing to the latter one).…”

“…At the same time, applicability of the theory of quantum corrections to conductivity (QCC) [2] was checked in detail for single crystals and ceramics of different doped manganites in our recent papers [6,7]. Let us mark briefly main results reported in [6,7] and compare it with these ones of commented paper [1].…”

“…Using numerical fittings of resistivity (ρ) vs. temperature (T) dependencies at the interval 4.2 -40 K, authors claim that the low temperature (LT) behavior of resistivity (shallow minimum and slight upturn at lowest T) may be account by 3D electron-electron interaction enhanced by disorder [2], as it was suggested previously in [3][4][5] for polycrystalline manganites. At the same time, applicability of the theory of quantum corrections to conductivity (QCC) [2] was checked in detail for single crystals and ceramics of different doped manganites in our recent papers [6,7]. Let us mark briefly main results reported in [6,7] and compare it with these ones of commented paper [1].…”