| AVS 56th International Symposium & Exhibition | |
| Magnetic Interfaces and Nanostructures | Thursday Sessions |
| Session MI+TF-ThA |
| Session: | Magnetic Thin Films: Multilayers and Nanostructures |
| Presenter: | Z.R. Tadisina, University of Alabama |
| Authors: | Z.R. Tadisina, University of Alabama A. Natarajarathinam, University of Alabama S. Gupta, University of Alabama T. Mewes, University of Alabama P. LeClair, University of Alabama E. Chen, Grandis, Inc. S. Wang, Grandis, Inc. W.F. Egelhoff, NIST |
| Correspondent: | Click to Email |
Spin transfer switching (STS) has been studied for CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJ) with perpendicular magnetic anisotropy (PMA) free and reference layers. The PMA multilayer material systems were studied as a function of bilayer thickness, bilayer ratio, and number of bilayers for Co/M multilayers, where M was Ni, Pd or Pt. After initial matrix experiments carried out to determine the experimental parameter space, a statistical Design of Experiments (DOE) was conducted to optimize the film structure that would maintain stable perpendicular anisotropy for a reasonable thickness of CoFeB, as well as minimize the damping parameter, α. For Co/Ni multilayers, the damping parameter varied from 0.016 to 0.023 as a function of the number of multilayers. As predicted and experimentally confirmed by others1,2, we observed a critical thickness of Co above which the PMA disappears and in-plane anisotropy is observed. The magnetic behavior of these PMA systems was studied by vector magnetometry and alternating gradient magnetometry. X-ray diffraction, transmission electron microscopy (TEM) and local electrode atom probe (LEAP) studies were carried out to investigate the structure of the multilayers, interface smoothness, and growth of (111) texture as a function of deposition conditions and post-deposition annealing. Stress and magnetic force microscopy (MFM) studies confirmed the presence of stripe domains in the PMA stacks. The resistance-area (RA) product and tunneling magnetoresistance (TMR) of the unpatterned MTJ stacks were tested by current-in-plane tunneling (CIPT) measurements to optimize the MgO barrier and PMA stacks prior to actual device fabrication. The transport properties of the patterned MTJ stacks were tested in a PPMS system for both field and current switching from 10K to 400 K to test the thermal stability of these devices.
References:
1. O. Hellwig, A. Berger, J. B. Kortright, and E. E. Fullerton, “Domain structure and magnetization reversal of antiferromagnetically coupled perpendicular anisotropy films,” J. Magn. Magn. Mater., vol. 319, pp.13–55, May 2007.
2. M. Tekielak, P. Mazalski, A. Maziewski, R. Schäfer, J. McCord, B. Szyman´ski, M. Urbaniak, and F. Stobiecki, “Creation of Out-of-Plane Magnetization Ordering by Increasing theRepetitions Number N in (Co/Au)N Multilayers,” IEEE Trans. Magn. vol. 44, pp. 2850-2853, November 2008.