DE-10 Thermal Effects on Damping Determination of Perpendicular MRAM Devices by Spin-Torque Ferromagnetic Resonance

The Gilbert damping plays an important role for understanding the switching behavior of perpendicular magnetic random-access memory (MRAM) cells. Damping measurements are typically made on full films of the free layer materials rather than on finished devices. It is to be expected that the damping is different between the device and the film level measurements [1,2,3]. Here we report on device level damping measurements using spin-torque driven ferromagnetic resonance. For all free layer materials investigated, we find that the extracted damping increases with decreasing device size and is higher than the respective film level values (Fig. 1). It is worked out that thermal agitation disturbs the resonance and causes an increase of the apparent damping. The effect is modeled by Langevin dynamics and good agreement with a variety of experimental details is obtained. An illustration of the thermal effect is shown in Fig. 2. For MRAM sizes bigger than about 55nm, the thermal agitation effect becomes negligible. Beyond the increase caused by thermal agitation, we believe that the device level damping is still somewhat higher than the film-level dampingReferences: [1] O. Ozatay et al., Nat. Mater. 7, 567 (2008). [2] H.T. Nembach et al., Phys. Rev. Lett, 110, 117201 (2013) [3] L. Thomas et al., IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, USA, 2017, pp. 38.4.1-38.4.4, (2017)