Probing Spin-Flip Scattering in Ballistic Nanosystems

Because spin-flip length is longer than the electron mean-free path in a metal, past studies of spin-flip scattering are limited to the diffusive regime. We propose to use a magnetic double barrier tunnel junction to study spin-flip scattering in the nanometer sized spacer layer near the ballistic limit. We extract the voltage and temperature dependence of the spin-flip conductance $G_s$ in the spacer layer from magnetoresistance measurements. In addition to spin scattering information including the mean-free path (70 nm) and the spin-flip length ($1.0–2.6\mu \mathrm{m}$) at 4.2 K, this technique also yields information on the density of states and quantum well resonance in the spacer layer.

Figure 1

A cross-sectional TEM image of a typical DBMTJ with Cu spacer. (a) is low-magnification image and (b) is the corresponding HRTEM images. The actual Cu thickness is much larger than the nominal thickness of 1.4 nm.

Figure 2

TMR ratio as a function of the magnetic field at RT (a), 77 K (b), and 4.2 K (c) for the CoFe (at 1 mV) and CoFeB (at 5 mV) DBMTJ samples.

Figure 3

Bias voltage dependence of $\gamma G_s$ for the CoFeB DBMTJ sample compared with theory (solid line). Inset: TMR as a function of bias voltage for the same sample.

Figure 4

Temperature dependence of $\gamma G_s$ for the CoFe and CoFeB DBMTJ samples.