The shot noise like feature of the magnetic 1/f noise in CoFeB/MgO/CoFeB magnetic tunnel junctions.

The magnetic field dependent 1/f noise in magnetic multilayers and magnetic tunnel junctions (MTJs) is conventionally considered as resistance fluctuations (S$_{\mathrm{R}})$, for which an applied current (I) is merely used to convert S$_{\mathrm{R}}$ to measurable voltage fluctuations (S$_{\mathrm{V}} \quad =$ I$^{\mathrm{2}}$S$_{\mathrm{R}})$. From S$_{\mathrm{R}}$ and magnetoresistance, magnetization fluctuations can be inferred obeying the fluctuation-dissipation relation (FDR), thus comes the name magnetoresistive noise. However, we find that 1/f noise in CoFeB/MgO/CoFeB MTJs is better described by S$_{\mathrm{I}}$/I, instead of S$_{\mathrm{V}}$/I$^{\mathrm{2}}$, particularly near the magnetic reversal fields of the reference layer and the free layer, the latter of which has not been previously investigated in detail. More surprisingly, the bias dependence resembles that of shot noise. These findings call for further investigation on FDR for magnetic noise in MTJs, especially in the far from equilibrium state with high bias and possible contribution from collective magnon excitations.