MAGNETIC AND ELECTRICAL CHARACTERIZATION OF Mg-B-O MAGNETIC TUNNEL JUNCTIONS UTILZING Fe60Co20B20 AND Ni65Fe15B20 FREE ELECTRODES.
J. C. Read1, H. W. Tseng2, Y. Li2, J. M. Pomeroy1, J. J. Cha3, P. Y. Huang2, W. F. Egelhoff, Jr. 1, D. A. Muller2, and R. A. Buhrman2
1. National Institute of Standards and Technology, Gaithersburg, MD
2. School of Applied and Engineering Physics, Cornell University, Ithaca, NY
3. Department of Materials Science and Engineering, Stanford University, Stanford, CA
Knowledge of the magnetic properties of the free layer electrode of a magnetic tunnel junction (MTJ) provides useful information with regards to MTJ layer structure, device design, and layer optimization. We present the results of magnetometry and ferromagnetic resonance (FMR) measurements of magnetic properties attributable to the Mg-B-O / free layer (Fe60Co20B20 or Ni65Fe15B20) electrode interface in Mg-B-O-based MTJs. We previously demonstrated that the tunnel barrier in our structures is Mg-B-O[1-3] and that we achieve high tunneling magnetoresistance (TMR) with low enough resistance area (RA) product values for use in spin transfer torque devices. We observe interlayer exchange coupling of these free layers to the MTJ reference layer due to interfacial roughness[5,6] which is dependent upon the temperature at which the structure was annealed. We measure a dependence of the surface perpendicular magnetic anisotropy[7-9] at the Mg-B-O barrier / free layer interfaces of these MTJ structures upon Mg-B-O barrier thickness and annealing temperature. Annealing these structures modifies the crystallinity of the electrode layers,[2,3,10] the tunnel barriers, and their interfaces, which is responsible for the modification of the magnetic properties of the MTJ thin film stacks. We also use magnetoresistance first order reversal curve (MR-FORC) analysis to measure the stability of free layer field-based switching in patterned device structures in an effort to assist identification of magnetic properties attributable to the patterning process as opposed to the MTJ thin film structure. These results indicate that many of the magnetic properties that are present in un-patterned MTJ stacks persist in patterned micron-scale devices.
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