Magnetotransport in polycrystalline La${}_{2/3}$Sr${}_{1/3}$MnO${}_3$ thin films of controlled granularity

Abstract

Polycrystalline La${}_{2/3}$Sr${}_{1/3}$MnO${}_3$ (LSMO) thin films were synthesized by pulsed laser ablation on single crystal (100) yttria-stabilized zirconia (YSZ) substrates to investigate the mechanism of magneto-transport in a granular manganite. Different degrees of granularity is achieved by using the deposition temperature (T${}_D$) of 700 and 800 ${}^0$C. Although no significant change in magnetic order temperature (T${}_C$) and saturation magnetization is seen for these two types of films, the temperature and magnetic field dependence of their resistivity ($\rho$(T, H)) is strikingly dissimilar. While the $\rho$(T,H) of the 800 ${}^0$C film is comparable to that of epitaxial samples, the lower growth temperature leads to a material which undergoes insulator-to-metal transition at a temperature (T${}_P$ $\approx$ 170 K) much lower than T${}_C$. At T $\ll$ T${}_P$, the resistivity is characterized by a minimum followed by ln $\text{T}$ divergence at still lower temperatures. The high negative magnetoresistance ($\approx$ 20) and ln $\text{T}$ dependence below the minimum are explained on the basis of Kondo-type scattering from blocked Mn-spins in the intergranular material. Further, a striking feature of the T${}_D$ = 700 ${}^0$C film is its two orders of magnitude larger anisotropic magnetoresistance (AMR) as compared to the AMR of epitaxial films. We attribute it to unquenching of the orbital angular momentum of 3d electrons of Mn ions in the intergranular region where crystal field is poorly defined.

26 pages, 7 figures

References in corpus (3)

• Grain boundary effects on magnetotransport in bi-epitaxial films of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$
• Superconducting and normal-state interlayer-exchange-coupling in La${}_{0.67}$Sr${}_{0.33}$MnO$3$-YBa${}_2$Cu${}_3$O${}_7-La$_{0.67}$Sr$_{0.33}$MnO${3}$ epitaxial trilayers
• Magnetization depinning transition, anisotropic magnetoresistance and inplane anisotropy in two polytypes of La${}_{2/3}$Sr${}_{1/3}$MnO${}_3$ epitaxial films

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