Spin tunneling in conducting oxides
- Hewlett-Packard Labs., Palo Alto, CA (United States)
Different tunneling mechanisms in conventional and half-metallic ferromagnetic tunnel junctions are analyzed within the same general method. Direct tunneling is compared with impurity-assisted, surface state assisted, and inelastic contributions to a tunneling magnetoresistance (TMR). Theoretically calculated direct tunneling in iron group systems leads to about a 30% change in resistance, which is close to experimentally observed values. It is shown that the larger observed values of the TMR might be a result of tunneling involving surface polarized states. The authors find that tunneling via resonant defect states in the barrier radically decreases the TMR (down to 4% with Fe-based electrodes), and a resonant tunnel diode structure would give a TMR of about 8%. With regards to inelastic tunneling, magnons and phonons exhibit opposite effects: one-magnon emission generally results in spin mixing and, consequently, reduces the TMR, whereas phonons are shown to enhance the TMR. The inclusion of both magnons and phonons reasonably explains an unusually bias dependence of the TMR. The model presented here is applied qualitatively to half-metallics with 100% spin polarization, where one-magnon processes are suppressed and the change in resistance in the absence of spin-mixing on impurities may be arbitrarily large. Even in the case of imperfect magnetic configurations, the resistance change can be a few 1,000%. Examples of half-metallic systems are CrO{sub 2}/TiO{sub 2} and CrO{sub 2}/RuO{sub 2}, and an account of their peculiar band structures is presented. The implications and relation of these systems to CMR materials, which are nearly half-metallic, are discussed.
- OSTI ID:
- 323413
- Report Number(s):
- CONF-971201-; ISBN 1-55899-399-1; TRN: IM9911%%26
- Resource Relation:
- Conference: 1997 fall meeting of the Materials Research Society, Boston, MA (United States), 1-5 Dec 1997; Other Information: PBD: 1998; Related Information: Is Part Of Science and technology of magnetic oxides; Hundley, M.F. [ed.] [Los Alamos National Lab., NM (United States)]; Nickel, J.H. [ed.] [Hewlett-Packard Labs., Palo Alto, CA (United States)]; Ramesh, R. [ed.] [Univ. of Maryland, College Park, MA (United States)]; Tokura, Yoshinori [ed.] [Univ. of Tokyo (Japan)]; PB: 375 p.; Materials Research Society symposium proceedings, Volume 494
- Country of Publication:
- United States
- Language:
- English
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