Low frequency noise in magnetic tunneling junctions with Co40Fe40B20/Co70.5Fe4.5Si15B10 composite free layer

• Magnetic tunneling junctions with CoFeB/CoFeSiB composite free layer.
• System study of low frequency noise of MTJs.
• Estimate the fluctuation moment of free layers.
• The temperature dependence of 1/f noise.

Magnetic tunneling junctions with Co40Fe40B20/Co70.5Fe4.5Si15B10 composite free layer have been fabricated and annealed at different temperatures to obtain the highest tunneling magnetoresistance. The field and temperature dependences of the low frequency noise have been measured to understand the origin of noise. The random telegraph noise has been observed at low magnetic field, and the corresponding fluctuating moment is estimated to be 4.8×105 μB with an effective area of 240 nm2. The dependence of noise on temperature was coincident with the thermally activated kinetics model above 30 K while it deviated from this model below 30 K. Studying the origin of the low frequency noise is helpful to reduce the noise level in MTJs.