Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions

Guan, Y.; Sun, J. Z.; Jiang, X.; Moriya, R.; Gao, L.; Parkin, S. S. P.
August 2009
Applied Physics Letters;8/24/2009, Vol. 95 Issue 8, p082506
Academic Journal
Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel junctions (MTJs). For this purpose, T-FMR measurements were conducted with an external magnetic field up to 14 kOe applied perpendicular to the film surface of MgO-based MTJs under a dc bias. The observed frequency-field relationship suggests that a 20 Å CoFeB free layer has an effective demagnetization field much smaller than the intrinsic bulk value of CoFeB, with 4πMeff=6.1±0.3 kOe. This value is consistent with the saturation field obtained from magnetometry measurements on extended films of the same CoFeB thickness. In-plane T-FMR on the other hand shows less consistent results for the effective demagnetization field, presumably due to excitations of more complex modes. These experiments suggest that the perpendicular T-FMR is preferred for quantitative magnetic characterization of nanoscale MTJs.


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