A.M. Mudarra Navarro

Extrinsic origin of ferromagnetism in single crystalline LaAlO3 substrates and oxide films

Commercial LaAlO3 substrates were thermally cycled simulating a procedure similar to those followed during TiO2 and SnO2 dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO2 films is of extrinsic origin.

ZnO:Co diluted magnetic semiconductor or hybrid nanostructure for spintronics?

We have studied the influence of intrinsic and extrinsic defects in the magnetic and electrical transport properties of Co-doped ZnO thin films. X-ray absorption measurements show that Co substitute Zn in the ZnO structure and it is in the 2+ oxidation state. Magnetization (M) measurements show that doped samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found that the values of the orbital L and spin S numbers are between 1 and 1.3 for L and S = 3/2, in agreement with the representative values for isolated Co 2+. The obtained negative values of the Curie–Weiss temperatures indicate the existence of antiferromagnetic interactions between transition metal atoms.