engleski

Co-doped (La, Sr)TiO_(3-delta): a high-Curie temperature diluted magnetic system with large spin-polarization

Spintronics applications require the use of highly spin-polarized current sources. Recently studies rely on the doping of host materials with magnetic ions (diluted magnetic semiconductors (DMS)) to achieve highly spin-polarized sources at high temperatures. We have followed this approach by doping metallic non-magnetic (La, Sr)TiO_3 with Co (Co-LSTO) in the range 0 – 3 %. We have grown Co-LSTO films by PLD on STO substrates. The films are ferromagnetic at room temperature, with a sizable magnetic anisotropy, which indicate the intrinsic nature of the ferromagnetism. To determine the spin polarization of Co-LSTO, we have grown Co-LSTO/LAO/Co heterostructures. On these samples we defined magnetic tunnel junctions of micrometric size by optical lithography. We performed tunneling magnetoresistance (TMR) experiments which demonstrate the existence of a large spin polarization (up to -80%) in Co-LSTO. We discuss both the temperature- and bias- dependence of the TMR. We have analyzed the composition and structure of Co-LSTO films at a local scale, by different techniques: High-Resolution Transmission Electron Spectroscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS) and Auger Electron Spectroscopy (AES). From these experiments we conclude that the Co distribution is homogeneous in the film with no Co-rich regions larger than 10 nm. Thus, we exclude Co-segregation as the origin of the ferromagnetism and TMR in Co-LSTO, and we conclude that the spin-polarization as well as the ferromagnetism are intrinsic properties of this DMOS. The present work represents an important step towards the understanding and application of the DMS approach to spintronic devices using complex oxide materials.

spintronics; spin polarization; magnetic oxides; tunnel magnetoresistance

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