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With a Curie point at 370 K, the half-metal (La 0.7 Sr 0.3 )MnO 3 (LSMO) is one of the most interesting candidates for electronic devices based on tunnel magnetoresistance. SrTiO 3 (STO) is up to now the best substrate for the epitaxy of suitable thin films of LSMO. The pseudocubic unit cell of rhombohedral LSMO has a parameter a LSMO such that ( a STO - a LSMO )/ a LSMO = + 0.83% (where a STO is the parameter of cubic STO) and an angle of 90.26°. As strained growth is tetragonal, relaxation implies recovery of both the pseudocubic parameter and of the original angle. In the LSMO layers that we prepare by pulsed-laser deposition, we show that these two processes are quite independent. The angular distortion is partially recovered by twinning in films 25 nm thick, while recovery of the parameter never occurs in the thickness range that we explored (up to 432 nm). A relaxation, however, takes place above a thickness of 100 nm, associated with a transition from two-dimensional to three-dimensional columnar growth. It is accompanied by chemical fluctuations. Our magnetic measurements exhibit Curie temperatures and magnetic moments very close to the bulk values in those layers where the crystal parameter is strained but the angle partially relaxed. [ABSTRACT FROM AUTHOR]

We have studied the pulsed laser deposition (PLD) of Zr1-xCexO2 and Ce1-xLaxO2-x/2 initially to grow buffer layers for perovskite films deposited on Si, LaAlO3, SrTiO3 and MgO and then to produce tunneling barriers for cuprate or manganite heterostructures. On (1 0 0) Si, the deposition of Zr1-xCexO2 (x = 0.12) produces a smooth epitaxial layer ( RRMS = 0.25/1 μm2), which allows the further deposition of high quality YBa2Cu3O7 (Tc ≥ 88 K) and La0.7Sr0.3MnO3 films. On the other hand, the use of Ce1-xLaxO2-x/2 (0≤ x ≤ 0.4) makes it possible to match the YBa2Cu3O7 and La0.7Sr0.3MnO3 layers to various substrates. The buffer layers are epitaxially grown with a 45° rotation of the in-plane axes with respect to those of the substrate, and the smoothness is high ( RRMS = 0.25/1 μm2). In the case of an ultra-thin barrier (≅2.5 nm) of Ce1-xLaxO2-x/2 sandwiched in a La0.7Sr0.3MnO3, the out-of-plane mismatch of 2 induces distortions at the interface steps, which propagate into the topmost La0.7Sr0.3MnO3 layer. This is in contrast to the case of SrTiO3 barriers where an ideal crystal continuity in the growth direction is observed. [ABSTRACT FROM AUTHOR]

The ac electrical impedance of a 400-nm-thick La[sub 0.67]Sr[sub 0.33]MnO[sub 3] thin film (on MgO) has been measured in the frequency range from 30 MHz up to 6 GHz using etched strips. The impedance is found to be nearly a constant resistance that is equal to the dc resistance. The only deviations, in the order of their magnitude, are: (i) the contact pad impedance at low frequency, (ii) a small inductive part in the impedance of the material, and (iii) a low decrease of the resistance above 3 GHz. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]