Thickness dependent transport properties of compressively strained La0.88Sr0.12MnO3 ultrathin films

Abstract

Thickness dependent magnetic and transport properties of compressively strained La 0.88 Sr 0.12 MnO 3 thin films grown on single crystalline SrTiO 3 ͑100͒ substrates have been studied. All films exhibit a large enhancement of ϳ130 K in T C / T IM as compared to that of the bulk target ͑T C ϳ 175 K͒. This has been explained in terms of suppression of the cooperative Jahn-Teller distortion due to in-plane compressive strain. The T C / T IM of the 5 nm film is 315 K/318 K and slightly increases for film thicknesses Յ25 nm. At higher film thicknesses, ϳ60 nm, the T C / T IM starts decreasing. At T Ͼ T IM , the electrical transport is due to thermally activated hopping of small polarons. The activation energy is found to be sensitive to film thickness and shows a minimum at around L ϳ 15-25 nm, which corresponds to the maximum of T C / T IM . All films possess large magnetoresistances ͑MRs͒ in the vicinity of room temperature. Low as well as high field MRs are observed to nearly double as the film thickness increases from 5 nm ͑MRϳ 28% / 3 T͒ to 60 nm ͑MR% ϳ 50% / 3 T͒. Thicker films ͑L Ն 25 nm͒ are found to exhibit sufficiently large temperature coefficients of resistivities, ϳ4% -5% / K, which could be suitable for bolometric applications.

Comparative study of transport properties of compressively strained epitaxial and polycrystalline La0.88Sr0.12MnO3 thin films

“…This upturn is more pronounced than that observed in the 6 nm thick films on LAO. We would like to mention that no such upturn was observed in similar films on SrTiO 3 [16]. Thus, the electrical transport characteristics of LSMO films on ZO are entirely different from the films on LAO or similar films on SrTiO 3 .…”

“…The possible reason for this could be that the present thin films show T C enhancement as a result of the compression strain. As explained elsewhere [8,9,16], the inplane compressive strain increases the inplane transfer integral…”

“…The appearance of only (00l) diffraction peaks shows that the films are coherently grown and oriented along the out-of-plane, that is, c-axis. At sufficiently small film thickness, the inplane lattice parameters are expected to take the same value as that of the substrate LAO (3.798 Å) [8,9,16]. Thus, the films are tetragonal distorted.…”

“…In view of the encouraging results obtained so far on compressively strained thin films of lightly doped manganites, such as La 1-x Sr x MnO 3 (x ∼ 0.10-0.12), a more comprehensive investigation of the evolution of magnetic and magnetotransport properties with film thickness, texture and nature is required. The variation in film thickness beyond a critical value leads to relaxation of the strain, resulting in formation of variety of lattice defects such as vacancies, stacking faults and dislocation networks [5,[10][11][12][13][14][15][16]. These defects are known to cause significant modifications in the magnetotransport and magnetic properties.…”

Enhanced ferromagnetic and metal insulator transition in Sm0.55Sr0.45MnO3 thin films: Role of oxygen vacancy induced quenched disorder

“…The resistivity of the S-A and S-O films were best fitted by the Emin-Holstein 13 small polaron hopping ͑SPH͒ in the adiabatic limit, given by ͑T͒ = AT exp͑E A / k B T͒ where the constant A is related to "n" the polaron concentration; "a" the site-to-site hopping distance, and "" the attempt frequency, k B is the Boltzmann constant and E A is the activation energy, which is approximated by E A Ϸ E P / 2, the polaron binding energy. 13 The experimental ᐉn͑ / T͒-1000/ T plot and the fit to data is shown in Fig. 4.…”