Naslov
Co-Doped (La, Sr)TiO_3: A High T_C Diluted Ferromagnet with Large Spin Polarization

Autori
Herranz, Gervasi ; Basletić, Mario ; Bibes, Manuel ; Ranchal, Rocio ; Jaffres, Henri ; Hamzić, Amir ; Tafra, Emil ; Maurice, Jean-Luc ; Colliex, C. ; Bouzehouane, Karim ; Jacquet, E. ; Contour, Jean-Pierre ; Barthélémy, Agnes ; Fert, Albert.

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

Izvornik
The IEEE International Magnetics Conference (INTERMAG 2006) / - San Diego (CA), 2006

Skup
The IEEE International Magnetics Conference (INTERMAG 2006)

Mjesto i datum
San Diego (CA), Sjedinjene Američke Države, 08.05.2006. - 12.05.2006

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
spintronics; spin polarization; magnetic oxides; high mobility; Shubnikov-de Haas oscillations

Sažetak
The research on magnetic semiconductors is one of the most relevant subjects of the nowadays spintronics. Remarkable advances have been achieved in diluted magnetic oxide systems (DMOS). Indeed, the discovery of room temperature ferromagnetism in Co-doped TiO_2 has triggered an intense research on other diluted systems, but the origin of ferromagnetism is not still well understood. However, there is a growing consensus on the role of extrinsic carriers (introduced by means of structural defects) on the mediation of ferromagnetic correlations. Most of these works have been aimed at the ferromagnetic properties, but a spin polarization of carriers is an essential requirement for the use of DMOS in spintronics. Here we report on the magnetic properties and spin polarization of (La, Sr)Ti_(1− x)Co_xO_3 (Co-LSTO) thin films, in which the host oxide is not a semiconductor but a strongly correlated metal with a high density of carriers. These films are ferromagnetic at room temperature and the magnetization is enhanced at the lowest oxygen growth pressures, indicating that oxygen vacancies may have an active role on the magnetism. As a direct way to probe the spin polarization, we have performed tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions associating Co-LSTO and Co electrodes. A large spin polarization of around -80% has been determined at low temperature, indicating that the carriers are highly spin-polarized in this system. We have carried out an extensive structural analysis of Co-LSTO combining high-resolution transmission electron microscopy, Auger electron spectroscopy and X-ray magnetic circular dichroism. As a result, we can exclude the presence of Co clusters in the Co-LSTO layer and thus, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. We report finally on planar magnetotransport experiments on Co-LSTO films grown on SrTiO_3 (STO) substrates. The electrical properties of these samples are strongly dependent on the growth conditions and large electronic mobilities as high as 10^4 cm^2/Vs at T = 10 K are observed for specimens grown at the lowest oxygen pressure. At high enough applied fields (above 6 Teslas) and low enough temperatures (below 4 K) Shubnikov-de Haas oscillations are also observed in the high-mobility samples. We present an extensive analysis of these quantum oscillations and relate them with the electronic properties of STO, for which we find large scattering rates up to 10 ps. Our results bring strong arguments for the DMOS approach with complex oxide materials in spintronics and give an opportunity to have a better understanding on the fundamental physical mechanisms leading to long-order magnetic order in diluted magnetic systems.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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