F. Pailloux

Strain relaxation in the epitaxy of La2/3Sr1/3MnO3 grown by pulsed-laser deposition on SrTiO3(001)

With a Curie point at 370 K, the half-metal (La0.7Sr0.3)MnO3 (LSMO) is one of the most interesting candidates for electronic devices based on tunnel magnetoresistance. SrTiO3 (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.

Magnetoresistance and spin electronics

We review several topics in the field of spin electronics: (i) giant magnetoresistance observed in magnetic multilayers; (ii) magnetization reversal by spin injection and (iii) spin-polarized tunneling in magnetic tunnel junctions combining electrodes of ferromagnetic transition metal and half-metallic oxide.

Review of recent results on spin polarized tunneling and magnetic switching by spin injection

We review recent results obtained at Orsay on two topics in the field of spin electronics: (i) Spin polarized tunneling in magnetic tunnel junctions combining electrodes of ferromagnetic transition metal and half-metallic oxide: we will describe the influence of the nature of the barrier on the sign of the spin polarization of electrons tunneling from the transition metal and we also discuss the temperature dependence of the TMR obtained with half metallic oxides. (ii) Magnetization reversal by spin injection: we will present and interpret experimental results obtained with pillar-shaped Co/Cu/Co trilayers.

Nanoscale analysis of a Co-SrTiO3 interface in a Magnetic tunnel junction

We use High Resolution Electron Microscopy together with Electron Energy Loss Spectroscopy to analyze the crystallography and the chemical configuration of a Co/SrTiO 3 interface in a Co/SrTiO 3 /La 2/3 Sr 1/3 MnO 3 magnetic tunnel junction. PACS: 75.47.-m, 75.70.Cn, 68.37.Lp, 79.20.Uv