AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI+SC-ThM

Paper MI+SC-ThM8
Ferromagnetic Co-doped Anatase TiO@sub 2@: Are All Growth Methods Created Equal?

Thursday, November 6, 2003, 10:40 am, Room 316

Session: New Spintronic Materials
Presenter: T. Droubay, Pacific Northwest National Laboratory
Authors: T. Droubay, Pacific Northwest National Laboratory
S.M. Heald, Pacific Northwest National Laboratory
T.C. Kaspar, University of Washington
C.M. Wang, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
Correspondent: Click to Email
With both theoretical and experimental underpinnings, a flurry of activity has centered around new candidate diluted magnetic semiconductors (DMS) based on doping semiconducting oxides with magnetic impurities. With a Curie point of ~700K, high remanence, and high saturation, Co-doped TiO@sub 2@ in the Anatase form stands out as the most magnetically robust oxide DMS. Following the initial discovery in 2001, several groups have explored the synthesis and properties of Co-doped anatase using an array of different growth methods. While most of these techniques produced materials exhibiting room temperature ferromagnetic behavior, the resounding message learned has been to accurately determine if minority phases are present. Thin film growth of this novel oxide material has been dominated by pulsed laser deposition (PLD) and oxygen plasma-assisted molecular beam epitaxy (OPA-MBE) on SrTiO@sub 3@(001) and LaAlO@sub 3@(001). We have consistently produced epitaxial materials by OPAMBE in which the saturation moment is consistently found to be ~1.1 - 1.3 µ@sub B@/Co at room temperature. In contrast, Co@sub x@Ti@sub 1-x@O@sub 2@ grown by PLD typically has a saturation magnetization at room temperature of 0.3 µ@sub B@/Co. We will discuss the similarities and differences between materials produced by these two techniques highlighting morphological, electrical and magnetic properties. We will also discuss our recent post-growth annealing study of MBE grown specimens in which the magnetic properties do not change when the films are annealed in vacuum at 825K. This is particularly interesting in light of recent seemingly contradictory results of annealed PLD grown films. Shinde et al. report that Co metal inclusions in an Anatase film can be dissolved within the matrix and substituted for Ti as a result of a 1200K anneal in 1atm. argon. In contrast, Kim et al. found that Co came out of solution and formed Co metal as a result of a 700K anneal in 10@sup -6@ torr O@sub 2@.