Ultra-smooth, highly ordered, thin films of La0.67Ca0.33MnO3±d

Abstract

We report the growth and characterization of ultra-smooth, highly ordered, strained La2/3Ca1/3MnO3±d thin films (approximately 600 Å in thickness). The thin films were deposited by ozone-assisted, block-by-block, molecular beam epitaxy on SrTiO3 (001) substrates without any post-deposition annealing. Scanning tunneling microscopy images showed oriented, unit-cell-high terraces characteristic of a step-flow growth mechanism. The root-mean-square roughness of the surface of an imaged film was determined to be 2 Å. This same film showed negative magnetoresistance values, [R(H=0)−R(Happlied)]/R(H=0), at 150 K of 93% and 5% in applied magnetic fields of 5.12 and 4×10−2 T, respectively.

Annealing assisted substrate coherency and high-temperature antiferromagnetic insulating transition in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

“…18,24,25 On the contrary, the terraced surface structures are commonly observed in the epitaxial films grown in the well-controlled step-flow or layer-by-layer mode, which usually signifies an defect-free structure and coherent strain state. 4,16,24,40 Furthermore, the symmetry mismatch, which is originated from the differences in octahedral configurations between the film and substrate, has been reported to increase the surface roughness. 5 These facts clearly reveal that the surface morphology could intrinsically manifest the structure coherency between film and substrate.…”

Onset of metallic behavior in strained(LaNiO3)n/(SrMnO3May1, Santos2, Bhattacharya3 2009Phys. Rev. B5913450View full textAdd to dashboardCite

“…The samples were grown by depositing a single elemental layer at a time. [14][15][16] Brief anneal periods ͑15-25 s͒ followed the completion of each metal-oxide layer. For example, deposition of a SMO/LNO bilayer on SrTiO 3 would be shuttered as follows: TiO 2 ͑substrate͒/SrO/ anneal/MnO 2 / anneal/ LaO/ anneal/ NiO 2 / anneal.…”

Disorder effects in epitaxial thin films of (La,Ca)MnO3

“…However, postannealing is often undesirable if the goal is to combine films with different physical properties ͑e.g., CMR and high-T c materials͒, nor is it a prerequisite for producing epitaxial and smooth films. 4,5 On the other hand, such epitaxial films usually show lower T c 's and spreads in T p values. Understanding the differences between films and bulk material is necessary both for applications involving heteroepitaxy ͑e.g., spin devices or tunnel junctions͒, and for elucidating the link between the microstructure and MR behavior.…”

“…However, biaxial strain can have an equal or even larger effect on T c , as was recently argued by Millis et al 10 We believe, therefore, that our measured values are intrinsic for epitaxial, strained LCMO on STO, which is corroborated by similar values reported previously. 4,5,11 Note that growth on LAO indicates different behavior, with strained, epitaxial films yielding T c values around 240 K. 11 Next, we turn to the behavior of the films with small d s . Figure 3͑b͒ shows the values for T p as well as for T c , while Fig.…”