Pinholes and temperature-dependent transport properties of MgO magnetic tunnel junctions

• Type: Article in International Scientific Journal
• Date: 2008

Authors

ventura, j. (Author) REIT; teixeira, j. m. (Author) Other; araujo, j. p. (Author) FCUP; sousa, j. b. (Author) FCUP; wisniowski, p. (Author) Other; freitas, p. p. (Author) Other

Journal

Title: Physical Review B - Condensed Matter and Materials Physics

Vol. 78

ISSN: 1098-0121

Publisher: American Physical Society

Indexing

ISI Web of Knowledge - 25 Citations

Scopus - 25 Citations

Other information

Authenticus ID: P-003-YA9

DOI: 10.1103/physrevb.78.024403

Abstract (EN): Magnetic tunnel junctions (MTJs) with thin crystalline MgO(001) barriers displaying large tunnel magnetoresistance (TMR) and low resistance-area product (RA) will likely be used as the next generation sensors in read heads of ultrahigh-density hard drives. However, the thin insulating barrier may result in the presence of metallic pinholes joining the two electrodes. Here we study the transport properties of thin MgO-based low resistance MTJs (barrier thickness t=7.5 A), deposited by magnetron sputtering, with RA values of similar to 40 Omega mu m(2), reaching TMR values of similar to 60-75% at room temperature. We performed temperature-dependent (300-20 K) resistance (R) measurements and observed different behaviors for different magnetic states: positive dR/dT for the parallel (P) state, attributed to the presence of pinholes in the barrier, but a mixed character in the antiparallel (AP) state, with dR/dT changing from negative to positive with decreasing temperature. This indicates an interesting competition between tunneling and metallic transport in the studied samples. To explain this transport behavior, we developed a simple model with the two conducting channels, tunnel and metallic, in parallel. The model assumes a linear variation of the electrical resistance with temperature for both conducting channels and its dependence on the MTJ magnetic state (P and AP). The modeled results show that the sign of dR/dT does not give an indication of the dominant conductance mechanism and that the crossover temperature at which dR/dT changes sign depends strongly on the linear electrical resistance-temperature coefficients. We performed fits to our experimental R(T) data, using the proposed model, and observed that such fits reproduced the data quite well, illustrating the validity of the model.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7