Naslov
Study of the origin of the spin polarization in the Co-doped (La, Sr)TiO_3 diluted magnetic oxide

Autori
Copie, Olivier ; Herranz, Gervasi ; Bibes, Manuel ; Mattana, Richard ; Petroff, Frederic ; Bouzehouane, Karim ; Jaffres, Henri ; Jacquet, Eric ; Maurice, Jean-Luc ; Cros, Vincent ; , Basletić, Mario ; Tafra, Emil ; Hamzić, Amir ; Barthélémy, Agnes ; Bencok, P.

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
IEEE International Magnetics Conference – Intermag Europe 2008, Madrid (Španjolska) / - Madrid, 2008

Skup
IEEE International Magnetics Conference – Intermag Europe 2008

Mjesto i datum
Madrid, Španjolska, 04.05.2008. - 08.05.2008

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
spintronics; magnetic oxides

Sažetak
Spintronics applications require the use of highly spin-polarized current sources. For this purpose, half-metallic ferromagnets, such as various magnetic oxides, have been integrated in spintronics devices and high magnetoresistance values have been recorded. However, their Curie temperatures are too close to room temperature for technological applications. Another possibility to achieve high spin-polarized sources at high temperatures consists of doping the host materials with magnetic ions, as in diluted magnetic semiconductor. We have followed this approach by doping metallic non-magnetic (La, , Sr)TiO_3 with 1, 5% Co (CoLSTO). The samples were grown by pulsed laser deposition on STO (001) substrates. In order to understand the origin of the magnetic properties of our CoLSTO samples (they revealed magnetic hysteresis cycles), we have performed a broad study including micro- and nano-structural characterization, as well as the measurement of the spin-polarization through the analysis of the magnetotransport properties of tunnel junction devices using CoLSTO electrodes. Quite interestingly, we have found that growth conditions, such as oxygen partial pressure, have a relevant influence on the magnetic properties, probably revealing the role of defects, including oxygen vacancies, on the mechanisms leading to magnetic correlations. It is well known that phase segregation is a major concern in these magnetic diluted systems. Bearing this in mind, we have performed an extensive structural analysis of our samples combining X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS) and Auger spectroscopy. None of these experiments showed any direct evidence for the presence of Co-rich clusters. To measure the spin polarization, CoLSTO tunnel junction devices with micro- and nanometric size have been fabricated either by optical lithography or by real-time resistance-controlled nanoindentation with a conductive AFM tip. The measurements of the tunnel magnetoresistance (TMR) for the CoLSTO/LAO/Co junctions gave the TMR values up to 20%. Our TMR results enabled us to deduce that a spin polarization for the CoLSTO system is up to 80%. We will address the dependence of the TMR and spin polarization on temperature and applied voltage bias, as well as the influence of growth conditions on the magnetotransport properties of these tunnel devices, with particular emphasis on the growth oxygen pressure. In order to analyze better the origin of the ferromagnetism and spin polarization of CoLSTO films, we have carried out XMCD (X-ray Magnetic Circular Dichroism) experiments. These experiments have provided us with useful insights into the electronic states at the Co and Ti sites, which are relevant to understand the microscopic origins of the magnetic properties of the CoLSTO films. In particular, we will show that the spectral signature of both XAS (X-ray Absorption Spectroscopy) and XMCD indicates that cobalt is in ionic states.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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