Tunneling-like magnetoresistance in bicrystal La0.8Sr0.2MnO3−δ thin films

Abstract

Epitaxial ferromagnetic La0.8Sr0.2MnO3−δ films have been sputtered on SrTiO3 bicrystal substrates. Etched patterns crossing the bicrystal grain boundary are compared with identical patterns not crossing it. The films were annealed at different conditions and their magnetoresistance measured as a function of temperature T and of in plane magnetic field H strength and direction. Annealing at 900 °C was found to modify the grain boundary and to increase its magnetoresistance. For H=±80 Oe parallel to the grain boundary and T=32 K narrow magnetoresistance peaks of 60% height are measured. They are interpreted in the frame of an in plane magnetotunneling structure.

Current dependence of grain boundary magnetoresistance in La0.67Ca0.33MnO3 films

“…5. For very low bias voltages a nearly parabolic behavior of the differential conductivity, as predicted by the Simmons model, was found by Steenbeck et al 8 . However, the inclusion of high bias current data in our measurements results in stronger systematic deviations of a Simmons model from the experimental data at low voltages.…”

“…Other approaches are to produce polycrystalline films 3 , bulk materials 4 , ramp-edge junctions 5 , or thin films which are under compressive strain 6 . As is well known from the high-T C superconductors, a further access is to deposit thin manganite films on bicrystal substrates to realize a single artificial grain boundary (GB) 7,8 . In order to understand the mechanism of the large lowfield MR, we have carefully studied the resistivity of thin manganite films with and without an artificial GB, induced by a bicrystal substrate, as a function of temperature, magnetic field and current.…”

La0.7Sr0.3MnO3Thin-Film Grain-Boundary Junctions on a Bi-Crystal Substrate

“…1. We did not observe any maximum of the R(T ) curves below the Curie temperature for our junctions, in contrast to the results described in papers [5] and [6]. Our grain-boundary junctions had quite low resistivities at room temperature, with R J A values around 3 × 10 −5 Ωcm 2 (A is the junction cross-section).…”

“…1). In contrast to the preparation details described in [5] and [6], we did not anneal our samples after the ion-etching process. All resistance measurements and current-voltage (I−V ) characteristics were recorded in a liquid helium-dewar using a Keithley 236 source-measure unit and a sensitive digital voltmeter (Keithley 182) for voltages below 1000 mV.…”

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

“…[10][11][12] Most of the systematic investigations devoted to individual grain boundaries have thus been carried out in thin films. By growing epitaxial thin films on bicrystal substrates, [13][14][15][16][17][18] well-controlled grain boundaries can be obtained. For example, Evetts et al 18 have studied films patterned in such a way that only the contribution of the grain boundary to the resistance is measured.…”