Magnetic field and angle dependences of the critical current density J c ͑H , ͒ in epitaxial c-oriented YBa 2 Cu 3 O 7−␦ thin films are measured by the four-probe transport current technique, low-frequency ac magnetic susceptibility, and superconducting quantum interference device magnetometry. The films under study are deposited by off-axis dc magnetron sputtering onto r-cut sapphire substrates buffered with a CeO 2 layer. A consistent model of vortex pining and supercurrent limitation is developed and discussed. Rows of growthinduced out-of-plane edge dislocations forming low-angle boundaries ͑LAB's͒ are shown to play a key role in achievement of the highest critical current density J c ജ 2 ϫ 10 6 A/cm 2 at 77 K. The model takes into account the transparency of LAB's for supercurrent as well as the pinning of vortex lattice on a network of LAB's. Principal statistical parameters of the film defect structure, such as the domain size distribution and mean misorientation angle, are extracted from J c ͑H͒ curves measured in a magnetic field H applied parallel to the c axis and from x-ray diffraction data. An evolution of angle dependences J c ͑͒ with H is shown to be consistent with the model supposing dominant pinning on edge dislocations. Strongly pinned vortices parallel to the c axis appear to exist in tilted low magnetic fields up to a characteristic threshold field, below which the magnetic induction within the film obeys a simple relation B = H cos . This feature is shown to explain the absence of the expected maximum of J c ͑͒ at H ʈ c in a low applied field. A peak of J c ͑H͒ and an angular hysteresis of J c ͑͒, which have been observed in an intermediate-field range, are discussed in terms of film thickness, surface quality, and orientation of the applied field. The observed effects are found to be consistent with the developed model. DOI: 10.1103/PhysRevB.73.054508 PACS number͑s͒: 74.25.Sv, 74.72.Bk, 74.78.Bz lated disorder ͑e.g., by random pointlike pins͒, the J c ͑H , ͒ dependence is determined by a single parameter H͑cos 2 + 2 sin 2 ͒ 1/2 , 12,13 where = ͱ m ab / m c is the anisotropy parameter, =1/5-1/7 for YBCO. For the monotonic decreasing J c ͑H , =0͒ dependence the scaling naturally yields the J c ͑H = const, ͒ dependence with a minimum at = 0 and a maximum at = /2.Moreover, a maximum of the J c ͑H , ͒ dependence at H ʈ c was shown ͑e.g., Ref. 6͒ to be absent for YBCO films. Ironically, many researchers considered this observation to be strong evidence for the absence of out-of-plane linear pins or their ineffectiveness for vortex pinning in epitaxial films. In a contrast, recently Maiorov et al. have observed the J c ͑H , ͒ peak at H ʈ c. 14 The maximum does exist and tends to shift PHYSICAL REVIEW B 73, 054508 ͑2006͒

Abstract-Magnetic field and temperature dependencies of the critical current density, ( ) were measured by SQUIDmagnetometry, ac magnetic susceptibility, and dc transport current techniques in the single-crystalline epitaxially-grown by offaxis dc magnetron sputtering YBa 2 Cu 3 O 7 (YBCO) films with ( 77 K) 2 10 6 A/cm 2 . The mechanism of vortex depinning from growth-induced linear defects, i.e., out-of-plane edge dislocations in low-angle tilt domain boundaries, is shown to describe quantitatively measured (). The developed model takes into account a statistical distribution of the dislocation domain boundaries ordered in a network as well as the interdislocation spacing within boundaries. Actual structural features of YBCO film known from HREM data turn out to be extracted from ( )-curves by a fitting procedure within the proposed model.

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The microstructural and the magnetotransport properties of La 0.7 Ca 0.3 MnO 3 and La 0.7 Sr 0.3 MnO 3 films, deposited on a BaTiO 3 layer ͑LCMO/BTO and LSMO/BTO, respectively͒, and on LaAlO 3 and SrTiO 3 ͑001͒ single crystals ͑LCMO/LAO, LSMO/LAO and LSMO/STO͒ by rf-magnetron sputtering using the "soft" ͑or powder͒ targets, have been investigated. The films grown on BTO demonstrate biaxial tensile in-plane and compressive out-of-plane strains, while those grown on LAO show the opposite trend, i.e., compressive in-plane and tensile out-of-plane strains. The films with a biaxial tensile in-plane strain undergo the magnetic transition at a higher temperature than those with a biaxial compressive one. This implies that the variation of Mn-O-Mn bond angle, controlled by the lattice strain, plays a more important role in the formation of spin ordering in the manganite film than the modification in the Mn-O bond length does. It was shown that the magnetic inhomogeneity, observed through the difference between field-cooled and zero-field-cooled temperature-dependent magnetization, is not greatly relevant to the electronic nature, but is controlled by the lattice distortion and the microstructural defects. The observed enhancement of magnetoresistance for the LSMO/BTO bilayer at room temperature makes this material system promising in the development of new hybrid ferromagnetic/ferroelectric devices.