Influence of chemical and magnetic interface properties of Co-Fe-B/ MgO / Co-Fe-B tunnel junctions on the annealing temperature dependenceof the magnetoresistance
The knowledge of chemical and magnetic conditions at the Co{sub 40}Fe{sub 40}B{sub 20}/MgO interface is important to interpret the strong annealing temperature dependence of tunnel magnetoresistance of Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions, which increases with annealing temperature from 20% after annealing at 200 C up to a maximum value of 112% after annealing at 350 C. While the well defined nearest neighbor ordering indicating crystallinity of the MgO barrier does not change by the annealing, a small amount of interfacial Fe-O at the lower Co-Fe-B/MgO interface is found in the as grown samples, which is completely reduced after annealing at 275 C. This is accompanied by a simultaneous increase of the Fe magnetic moment and the tunnel magnetoresistance. However, the TMR of the MgO based junctions increases further for higher annealing temperature which can not be caused by Fe-O reduction. The occurrence of an x-ray absorption near-edge structure above the Fe and Co L-edges after annealing at 350 C indicates the recrystallization of the Co-Fe-B electrode. This is prerequisite for coherent tunneling and has been suggested to be responsible for the further increase of the TMR above 275 C. Simultaneously, the B concentration in the Co-Fe-B decreases with increasing annealing temperature, at least some of the B diffuses towards or into the MgO barrier and forms a B{sub 2}O{sub 3} oxide.
- Research Organization:
- COLLABORATION - Thin Films and Nano Structures,Department of Physics, Bielefeld University, 33501 Bielefeld,Germany
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 932528
- Report Number(s):
- LBNL-63478; JAPIAU; TRN: US0803553
- Journal Information:
- Journal of Applied Physics, Vol. 102, Issue 5; Related Information: Journal Publication Date: 09/2007; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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