Near-interface magnetotransport in La_0.75Sr_0.25MnO₃ epitaxial films on SrTiO₃ substrate

Abstract

The magnetotransport properties of La0.75Sr0.25MnO3 (LSMO) films epitaxially grown on SrTiO3 (0 0 1) substrate were studied. The Curie temperature (Tc) of LSMO films decreases from 300 to 105 K with a reduction in the film thickness to 5 nm. A clear metal–insulator transition is observed at a temperature consistent with Tc for films thicker than 10 nm. However, the 5 nm thick film displays an insulative characteristic along with a high magnetoresistence effect in a wide range of temperatures below and above Tc. A phase-separation phenomenon in the 5 nm thick film was demonstrated by thermally activated hopping transport between ferromagnetic metallic domains embedded in an insulative matrix at temperatures below Tc, but between paramagnetic metallic domains at temperatures above Tc. It was also confirmed by conductive atomic force microscopy images.

Surface characterization of ultrathin La0.75Sr0.25MnO3 epitaxial films on SrTiO3 substrate

“…The decrease of Mn 3+ /Mn 4+ ratio indicates the reduction of itinerant electrons for electrical conduction causing the increase of resistivity with decreasing LSMO film thickness, as observed in our previous temperature-dependent resistivity measurement [6]. The CAFM images of the LSMO films also display a consistent observation.…”

Structure determination of monolayer-by-monolayer grownLa1−xSrxMnO3thin films and the onset of magnetoresistance

“…We get a negative magnetoresistance ratio ⌬R / R B = ͑R B − R 0 ͒ / R B = −7% at 310 K. This value is far from being "colossal," but consistent with other experimental observations for comparably thin films. 7,8 The curves do not show the usual metal-insulator transition that one might expect for thicker, bulklike films. Instead, they resemble more semiconducting behavior, indicating the presence of an electrical dead layer at the substrate-film interface.…”

“…This parameter also accounts for possible surface roughness, although the root mean square roughness is known to be only 1 to 2 Å for films of several tens of nanometers thickness. 7,27…”

“…This has been explained by the presence of an electrical "dead layer" at the substratefilm interface. [7][8][9] Nevertheless, such films still exhibit magnetoresistive behavior. 7 Our intention is thus to use exact atomic coordinates to correlate the structure with the transport properties, in order to determine a minimum thickness for the onset of magnetoresistance.…”

Magneto-Electric Coupling in PbZr0.53Ti0.47O3/CoFe2O4 Layered Thin Films

“…The M s and M r values were larger for L3 compared to L5 and L9. This could be attributed to the presence of magnetically "dead" layers between the CFO and PZT interfaces with increasing numbers of layers [27];. The temperature variation of M r for L3, L5, and L9 MLs structures are shown in Fig.…”