11 2016

Conference Talk: Measurement and Characterization of Nonlinearities in Magnetic Tunnel JunctionsKate Auerbach

It has been observed that I-V curves of magnetic tunnel junctions (MTJs) exhibit nonlinear and asymmetric characteristics [1]. Voltage-dependent nonlinearity and asymmetry in MTJ devices can then be fitted into a model [2].

In this work, we present a measurement setup that allows us to directly measure harmonic power (Fig. 1). Such harmonic analysis reveals that nonlinearity order in MTJ devices depends on the device bias voltage (Fig. 2).

We also discuss the reasons for nonlinearities: 1) nonlinear R(V) response of an MTJ device and 2) spin transfer torque (STT), which is asymmetric with respect to the device bias voltage. The measurements are compared with finite-element micromagnetic simulations, which solve the coupled micromagnetic/spin drift-diffusion equations taking inherently the field-like and damping-like STT into account [3]. From this analysis these two causes of nonlinearities are distinguished.

Figure 1
Fig. 1. Experimental Setup. Signal Generator is set at 1GHz. Bandpass Filter 1 is used to eliminate higher-order harmonics from the Signal Generator. DC Power Supply provides the device bias voltage. Bandpass Filter 2 is tuned to the second or third harmonic.
Figure 2
Fig. 2. Second (red, solid) and third (blue, dashed) harmonics of the MTJ device.

[1] J. Z. Sun & D. C. Ralph, "Magnetoresistance and Spin-Transfer Torque in Magnetic Tunnel Junctions," J. Magn. Magn. Mater. 320, 1227-1237, 2008.
[2] J. Zang & R. M. White, "Voltage Dependence on Magnetoresistance in Spin Dependent Tunneling Junctions," J. Appl. Phys., vol. 83, no. 11, 1998.
[3] Abert, C. et al., "A three-dimensional spin-diffusion model for micromagnetics," Sci. Rep. 5, 14855, 2015.

For more information, visit the conference website and see my presentation.

Go Back