Noise spectroscopy of CoFeB/MgO/CoFeB magnetic tunnel junctions in the presence of thermal gradients

• Thermal gradients induced magnetization dynamics on MTJ structures are explored.
• Magnetic noise spectroscopy is carried out to study the efficiency of such effects.
• A decrease of resonance frequency is observed at both MTJ states for large ∇T.
• An asymmetric linewidth behavior is observed for both MTJ states under ∇T.
• Additional thermal effects beyond thermal activation must be considered.

We present experimental data of the precessional dynamics of the free layer of CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The free layer precession is investigated by noise spectroscopy. Thermal gradients of the order of tens of mK/nm across the MTJ are generated by electrical heating. Without applied thermal gradients we find spin transfer torque modified magnetization precession. With increasing thermal gradients we generally observe a decrease of the precession frequency which could be related to an increasing overall free layer temperature. However an asymmetry of the line width behavior for parallel and antiparallel orientation points towards additional effects beyond thermal activation. This could be a hint for the modification of the precessional dynamics in magnetic tunnel junctions by thermal spin torques.