Structural and functional characterization of (110)-oriented epitaxial La2∕3Ca1∕3MnO3 electrodes and SrTiO3 tunnel barriers

Abstract

La 2/3 Ca 1/3 MnO 3 ͑LCMO͒ films have been deposited on ͑110͒-oriented SrTiO 3 ͑STO͒ substrates. X-ray diffraction and high-resolution electron microscopy reveal that the ͑110͒ LCMO films are epitaxial and anisotropically in-plane strained, with higher relaxation along the ͓1-10͔ direction than along the ͓001͔ direction; x-ray absorption spectroscopy data signaled the existence of a single intermediate Mn 3+/4+ 3d-state at the film surface. Their magnetic properties are compared to those of ͑001͒ LCMO films grown simultaneously on ͑001͒ STO substrates It is found that ͑110͒ LCMO films present a higher Curie temperature ͑T C ͒ and a weaker decay of magnetization when approaching T C than their ͑001͒ LCMO counterparts. These improved films have been subsequently covered by nanometric STO layers. Conducting atomic-force experiments have shown that STO layers, as thin as 0.8 nm, grown on top of the ͑110͒ LCMO electrode, display good insulating properties. We will show that the electric conductance across ͑110͒ STO layers, exponentially depending on the barrier thickness, is tunnel-like. The barrier height in STO ͑110͒ is found to be similar to that of STO ͑001͒. These results show that the ͑110͒ LCMO electrodes can be better electrodes than ͑001͒ LCMO for magnetic tunnel junctions, and that ͑110͒ STO are suitable insulating barriers.

Strong uniaxial in-plane magnetic anisotropy of (001)- and (011)-orientedLa0.67Sr0.33MnO3thin films onBoschker1, Mathews2, Houwman3 et al. 2009Phys. Rev. B1174982View full textAdd to dashboardCite

“…For an MTJ with ͑011͒ pc interfaces between the electrodes and the barrier material, the top and bottom interfaces are expected to be symmetrical and without interfacial charge transfer. 8,9 The magnetic properties of LSMO films are known to be very sensitive to the strain imposed by the lattice mismatch between the film and the substrate. [10][11][12][13] Magnetic properties of LSMO thin films are mainly studied in systems with ͑001͒ pc -oriented LSMO, which is grown on SrTiO 3 ͑001͒ c , NdGaO 3 ͑NGO͒ ͑110͒ o , and LaAlO 3 ͑LAO͒ ͑001͒ pc .…”

Effect of the capping on the local Mn oxidation state in buried (001) and (110) SrTiO3/La2/3Ca1/3MnO3 interfaces

“…In contrast, those of the (110)LCMO and the corresponding (110)LCMO/STO C samples are somewhat rougher. This difference, commonly observed in (001) and (110) films on STO substrates [9][10][11] has been attributed to the inherent instability of the polar (110) surfaces.…”

“…10,11 The EELS data presented above provides an explanation of this at the microscopic level: upon growth of the STO capping on the (001)LCMO layer, a Mn mþ reduction appears near the capping/electrode interface. Conversely, in the case of (110)LCMO, the Mn mþ oxidation state remains unchanged after STO capping.…”

“…Structural and magnetic properties of the bare STO S // LCMO layers and STO S //LCMO/STO C have been reported elsewhere. 11 Here we just mention that reciprocal space maps indicated that the (001) LCMO film remained fully strained, while the (110) film was partially relaxed in the [1][2][3][4][5][6][7][8][9][10] direction (notice that LCMO / STO lattice mismatch is the same for both orientations, about 1.2%). From magnetization versus field curves, measured at 10 K, the saturation magnetizations of bare LCMO films M S were found to be M S (001) %543 emu/cm 3 and M S (110) % 570 emu/cm 3 , whereas for the capped electrodes the corresponding values were found to be about À10% and À3% smaller, respectively.…”

“…9 Quite similarly, magnetization and Nuclear Magnetic Resonance experiments on (001) and (110) LCMO films capped with nanometric layers of SrTiO 3 (STO C ) indicate that whereas the properties of the (110) LCMO are robust and quite insensitive to capping, this is not the case of STO-capped (001) LCMO which displays a significant reduction in magnetization. 10,11 It follows that some electronic reconstruction at the interface occurs upon capping the (001)LCMO films, which strongly affects their magnetic properties.…”