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^{1,a)}, Greg McKusky

^{1}and E. Dan Dahlberg

^{1,a)}

### Abstract

The low frequency noise in magnetic tunnel junctions was studied as a function of applied magnetic field. In magnetic states where the magnetization is reversing, the measurement indicates a spectrum whereas at all other applied fields a spectrum is observed. The spectra are found to be an artifact of the magnetic after effect. Without the artificial influence of the magnetic after effect, only spectra are observed.

We would like to acknowledge useful conversations with Randall Victora and that this work was supported primarily by the MRSEC Program of the National Science Foundation under Award Nos. DMR-0212302 and DMR-0819885.

### Key Topics

- Magnetic aftereffects
- 16.0
- 1/f noise
- 13.0
- Magnetic tunnel junctions
- 7.0
- Electric measurements
- 5.0
- Magnetic fields
- 5.0

## Figures

The measured resistance of one of the MTJ samples when the magnetic field is swept from positive to negative values is shown in (a). The three plots in (b) are PSDs taken at the points A, B, and C marked in the resistance curve. The PSD taken at the point marked E is similar to that at point A; the same is true for points D and B. In each of the three plots the solid lines are either (for points A and C) or (for point B).

The measured resistance of one of the MTJ samples when the magnetic field is swept from positive to negative values is shown in (a). The three plots in (b) are PSDs taken at the points A, B, and C marked in the resistance curve. The PSD taken at the point marked E is similar to that at point A; the same is true for points D and B. In each of the three plots the solid lines are either (for points A and C) or (for point B).

(a) Magnetoresistance curve, solid curve in (a) and the value of the PSD at 1 Hz (squares). (b) The exponent as a function of magnetic field where is obtained by fitting for each spectrum at low frequencies.

(a) Magnetoresistance curve, solid curve in (a) and the value of the PSD at 1 Hz (squares). (b) The exponent as a function of magnetic field where is obtained by fitting for each spectrum at low frequencies.

As a constant current is applied, the MTJ voltages are measured as functions of time at different magnetization configurations. The data in (a) are taken in the P state such as point E in Fig. 1 , those in (b) are taken when the magnetization is switching from the P to AP state (soft layer switch) such as point D in Fig. 1 , while the data in (c) correspond to the MTJ in an AP state such as point C in Fig. 1 , and lastly the data in (d) correspond to the magnetic transition from the AP to P state (hard layer switch) similar to point B in Fig. 1 . Note that (b) and (d) have larger vertical scale gradations. The inset in (b) is the same as the P to AP data plotted using a logarithmic scale for the time as is usually done for the magnetic after effect.

As a constant current is applied, the MTJ voltages are measured as functions of time at different magnetization configurations. The data in (a) are taken in the P state such as point E in Fig. 1 , those in (b) are taken when the magnetization is switching from the P to AP state (soft layer switch) such as point D in Fig. 1 , while the data in (c) correspond to the MTJ in an AP state such as point C in Fig. 1 , and lastly the data in (d) correspond to the magnetic transition from the AP to P state (hard layer switch) similar to point B in Fig. 1 . Note that (b) and (d) have larger vertical scale gradations. The inset in (b) is the same as the P to AP data plotted using a logarithmic scale for the time as is usually done for the magnetic after effect.

The fitted value of the exponent (circles) and the magnitude of the PSD at 1 Hz (squares) as functions of time at fixed fields in transition regions. The plot (a) corresponds to the P to AP transition (soft layer reversal) and the plot (b) is that of the AP to P transition (hard layer reversal).

The fitted value of the exponent (circles) and the magnitude of the PSD at 1 Hz (squares) as functions of time at fixed fields in transition regions. The plot (a) corresponds to the P to AP transition (soft layer reversal) and the plot (b) is that of the AP to P transition (hard layer reversal).

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