Effect of strain and tetragonal lattice distortions in doped perovskite manganites

Abstract

A series of high-quality, coherently strained ͓La 2/3 ͑Ca or Ba͒ 1/3 MnO 3 / SrTiO 3 ͔ ϫ N superlattices has been prepared on ͑100͒ SrTiO 3 and NdGaO 3 substrates by laser molecular beam epitaxy. The manganite layers are biaxially strained due to lattice mismatch. A quadratic decrease of the metal-to-insulator transition temperature T p with increasing biaxial distortion bi 2 both for tensile and compressive in-plane strain is found. For T Ͼ T p , the resistivity versus temperature curves could be well described by the small polaron hopping model with the polaron binding energy increasing with increasing bi 2 . Furthermore, the magnetoresistance of the manganite films was found to strongly increase with increasing bi 2 or decreasing T p , respectively, following a universalbehavior. An anomalous upturn of resistivity in the low-temperature regime ͑T Ͻ 25 K͒ was detected, which may be attributed to enhanced Coulomb interaction of the charge carriers resulting from disorder due to the lattice distortion. Our analysis clearly demonstrates the importance of biaxial strain and Jahn-Teller-type lattice distortions for the physics of the doped manganites. It is shown that epitaxial coherency strain can be used to deliberately modify the materials properties.

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

“…We stress that this experimental observation contrasts with the common assumption that the Poisson law holds when evaluating cell parameters of manganite thin films. 4,23 The small expansion of the unit cell may reflect the existence of some oxygen deficiency.…”

Effect of biaxial strain on the electrical and magnetic properties of (001) La0.7Sr0.3MnO3 thin films

“…[6][7][8][9][10][11][12][13][14][15][16] In this work, we investigate the magnetotransport properties of fully commensurate epitaxial La 0.7 Sr 0.3 MnO 3 thin films grown by reactive molecular-beam epitaxy. Our films span a biaxial strain range from Ϫ2.3% to +3.2%, and we find excellent agreement between the measured Curie temperatures and the model of Millis et al 5 The films were grown on nine commercially available perovskite substrates: ͑100͒ p LaAlO 3 , ͑001͒ LaSrGaO 4 , ͑110͒ NdGaO 3 , ͑100͒ ͑LaAlO 3 ͒ 0.3 -͑SrAl 0.5 Ta 0.5 O 3 ͒ 0.7 ͑LSAT͒, ͑100͒ SrTiO 3 , ͑110͒ DyScO 3 , ͑110͒ GdScO 3 , ͑110͒ SmScO 3 , and ͑110͒ NdScO 3 , where the subscript p indicates pseudocubic indices.…”

“…The obtained value is in reasonable agreement with the typical value for manganites. 7,19 The influence of biaxial strain on the temperature dependence of the resistivity ͑T͒ of the thin films grown on various substrates is shown in Fig. 4͑a͒.…”

Comment on ‘Structural properties and electrical resistivity of Na-substituted lanthanum manganites: La1−xNaxMnO3+y (x=0.1, 0.125 and 0.15)’ and ‘Structure and electrical resistivity of La1−xBaxMnO3 (0. 25≤x≤0.35) perovskites’

“…It is evident that the above values exceed on three to six orders of magnitude the usual LT resistivity of, e.g., typical transition metals. Note also that all previous more or less grounded attempts to extract quantum corrections to LT conductivity in epitaxial thin films or single crystals of doped manganites definitely evidence on a very weak influence of moderate H ∼ 10 T on their LT resistivity, see [6,12,13]. Thus, also the model [4] is inapplicable in this very case due to the following reasons: (i) the samples studied in [1,2] are not the single crystals and their LT resistivity is too high and (ii) the model [4] does not account for the evolution of LT (T,H) dependences in La 1−x Ba x MnO 3 ceramics upon H increase [2].…”