At room temperature a large magnetoresistance, IsR/R(H =0), of 60% has been observed in thin magnetic films of perovskitelike La-Ba-Mn-o, The films were grown epitaxially on SrTi03 substrates by oA'-axis laser deposition. In the as-deposited state, the Curie temperature and the saturation magnetization were considerably lower compared to bulk samples, but were increased by a subsequent heat treatment. The samples show a drop in the resistivity at the magnetic transition, and the existence of magnetic polarons seems to dominate the electric transport in this region. PACS numbers: 75.70.Ak, 72. 15.Gd, 73.50.Jt Giant magnetoresistance (GMR) due to spin-dependent scattering at the interface between ferromagnetic and nonmagnetic regions has been the subject of intense research in the last years [1-4]. At room temperature, resistance changes hR/R(H=0) as high as 40% have been observed in Cu/Co multilayers [2] and up to 11% in heterogeneous Cu/Co alloys [3,4], compared to only 2%-3% for "conventional" materials such as permalloy. A much higher magnetoresistance was found near a metal/insulator and simultaneous magnetic phase transition, e.g. , in Eu~-"Gd"Se [5], but in this material the eAect is restricted to temperatures below 50 K. The anomalous transport phenomena in these Eu-chalcogenide alloys have been explained by the appearance of giant spin molecules [6] and spin polarons [7]. Similar observations have been made in the mixed valence perovskitelike Ndo 5Pbo 5Mno3 in the region around the ferromagnetic phase transition at 184 K [8]. A large drop in resistivity and a high magnetoresistance AR/ R (0) & 50% was found, which is also believed to be caused by the existence of magnetic polarons. La2/3-Ba~g3Mno3 is also well known as a mixed valence metallic ferromagnet, but with a considerably higher Curie temperature of Tc =343 K [9,10]. At the Curie temperature a cusp in the resistivity was found and therefore gives rise to the assumption of a high magnetoresistance eAect at room temperature. Targets of stoichiometric composition were prepared by standard ceramic techniques from the metallic oxides and carbonates of 99.9% purity by repeated grinding and annealing in air. The x-ray diAraction patterns showed no other reAections than those of the rhombohedral unit cell found in Ref. [10] (a =0.3910 nm, y=90. 12'). Thin films of 150~10 nm thickness were grown on SrTi03 10&&10 mm substrates in (100) and (110) orientation. A laser deposition technique in off'-axis geometry was used, which had previously turned out to be a powerful tool in preparing high-T, superconducting thin films with a smooth surface [11]. Different substrate temperatures between 600 and 900 C were used, at a deposition pressure of 0.4 mbar oxygen. Epitaxial films were obtained for a substrate temperature of Tg =600 C as confirmed 250 T= 300K 200 8 A 0 bP c5 150 100 50 0:-0.0~a nnealed O 0.5 1.0 1.5 magnetic field p, H [T] 2.0 FIG. 1. Room temperature magnetization curve for the asdeposited sample (Ts =600'C) showing paramagnetic behav-ior. The ferroma...

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We investigate the influence of a well-defined reversible biaxial strain ≤ 0.12 % on the magnetization ( M ) of epitaxial ferromagnetic manganite films. M has been recorded depending on temperature, strain and magnetic field in 20 -50 nm thick films. This is

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