| AVS 57th International Symposium & Exhibition | |
| Magnetic Interfaces and Nanostructures | Thursday Sessions |
| Session MI+TF-ThM |
| Session: | Magnetic Nanostructures, Thin Films and Heterostructures |
| Presenter: | A. Natarajarathinam, University of Alabama |
| Authors: | A. Natarajarathinam, University of Alabama Z.R. Tadisina, University of Alabama S. Gupta, University of Alabama |
| Correspondent: | Click to Email |
Magnetic tunnel junctions with vanadium-based capping layers on top of the CoFeB free layer have been studied. The interest in the effect of capping on the free layer originated from reports(1) that cap layers influence the crystallization of the CoFeB free layer through diffusion of the B into the cap, as well as induce a partial perpendicular magnetic anisotropy (PPMA or PPA) in the free layer(2,3). Different cap layers differently accelerate the diffusion of the B from the free layer. In this study, we have sputter-deposited V/Ru and V/Ta capping layers on CoFeB and subsequently characterized these films by magnetometry and ferromagnetic resonance (FMR). We have found that V/Ru and V/Ta capping of CoFeB induces partial perpendicular anisotropy (PPA) in CoFeB, as well as reduces the Gilbert damping parameter, confirming results reported by other researchers(4). The origin of this PPA is believed to be caused by the interface anisotropy between the free layer and the capping layer. The effect of post-deposition annealing, CoFeB thickness, and doping of CoFeB with vanadium on the anisotropy and damping of these V/Ru and V/Ta capped samples has been studied for the free layers. Doping CoFeB with vanadium greatly reduces the 4πMs and 4πMeff values, resulting in an effective increase in the PPA, as well as the damping parameter. X-ray magnetic circular dichroism (XMCD) has also been performed on a series of V-doped films over a range of V concentrations. Magnetic tunnel junctions were fabricated to study device properties of the V-capped and V-doped films. The mechanisms for increasing TMR in these types of pMTJ’s will be discussed.
This work is supported by the U.S. Department of Defense DARPA-MTO STT-RAM Universal Memory contract, and Grandis Inc., Milpitas, CA.
1. T. Miyajima, T. Ibusuki, S. Umehara, M. Sato, S. Eguchi, M. Tsukada, and Y. Kataoka, Appl. Phys. Lett. 94, 122501 (2009).
2. E. Chen, D. Apalkov, Z. Diao, A. Driskill-Smith, D. Druist, D. Lottis, V. Nikitin, X. Tang, S. Watts, S. Wang, S. A. Wolf, A. W. Ghosh, J. W. Lu, S. J. Poon, M. Stan, W. H. Butler, S. Gupta, C. K. A. Mewes, T. Mewes, and P. B. Visscher, (invited paper), IEEE Trans. Magn. 46, 1 (2010).
3. S. M. Watts, X. Tang, Z. Diao, D. Apalkov, D. Druist, E. Chen, V. Nikitin "Low switching current in conventional in-plane STT-RAM structure with partial perpendicular anisotropy", Digest FV-11, 11th Joint MMM-Intermag Conference, Washington, DC (2010).
4. D. Worledge, D. Abraham, S. Brown, M. Gaidis, G. Hu, C. Long, J. Nowak, E. O’Sullivan, R. Robertazzi, J. Sun, P. Trouilloud, 11th Joint MMM-Intermag Conference, Washington, D. C. (2010).