Transport properties of some rare‐earth mono and bilayer manganite films

Abstract

AbstractWe report the transport properties of both single‐layer (SL) La0.67Sr0.33MnO3 (SL1), La0.67Ca0.33MnO3 (SL2) and La0.67Sr1.33MnO4 (SL3) each of thickness 135 nm and bilayers (BL) SL1/SL3 (BL1) and SL2/SL3 (BL2) each of thickness 270 nm. All the films are deposited on SrTiO3(001) substrates by the off‐axis RF sputtering process. Compared to SL films, a large enhancement of magnetoresistance (MR) at 1.2 T field is observed in the BL films. Except for the antiferromagnetic (AF) SL3 film, two ferromagnetic (FM) films SL1 and SL2 showed metallic transitions, respectively, at T MI = 248 and 365 K. For the BL films, T MI shifts largely towards a lower temperature than the corresponding T MI of the corresponding SL films due to the increase of disorder and strain effect at the junction of the films. Temperature‐dependent resistivity (ρ ) curves, above T MI, are best fitted by the adiabatic small‐polaron hopping model, i.e. ρ = ρ 0T exp (E a/k BT ) with activation energy E a (BL) > E a(SL). Within the temperature range T D/2 < T < T MI (T D being the Debye temperature), the resistivity curves are well fitted with the variable range hopping (VRH) with effective number of carriers at the Fermi level [N (E F)], being different for BL and SL films. In the SL films, spin ordering completes below a critical temperature (T *, say) and a changeover of the transport mechanism dominated by the electron–electron scattering regime (T < T *) to an electron–magnon‐dominated scattering regime (T > T *) is observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)