Nonadiabatic Spin Transfer Torque in High Anisotropy Magnetic Nanowires with Narrow Domain Walls

Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized $(\mathrm{Pt}/\mathrm{Co}{)}_3/\mathrm{Pt}$ multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.

Figure 1

(a) Polar Kerr rotation angle as a function of the magnetic field applied perpendicular to the film plane of the unpatterned $\mathrm{Pt}/(\mathrm{Co}/\mathrm{Pt}{)}_3$ film at room temperature. (b) SEM image of the structure; inset: SEM image of the Hall cross connected to the gold electrodes. (c) Hall resistance vs the perpendicular applied magnetic field at $T_{\mathrm{cryo}}=180\mathrm{K}$; the black curve (full squares) corresponds to a full hysteresis cycle, the red curve (down triangles) was measured while preparing the magnetic state to plateau A. For the blue curve (up triangles), current pulses of $-2.5\mathrm{mA}$ were injected before measuring the Hall resistance. $H_{\mathrm{dep}}$ is indicated for the black curve.

Figure 2

(a)–(b) $H_{\mathrm{dep}}$ as a function of $|I|$ for (a) a constant cryostat temperature of $T_{\mathrm{cryo}}=130\mathrm{K}$ (squares) and $T_{\mathrm{cryo}}=250\mathrm{K}$ (circles) and (b) a constant sample temperature of $T_{\mathrm{sample}}=250\mathrm{K}$ (up triangles) and $T_{\mathrm{sample}}=300\mathrm{K}$ (down triangles). Each point corresponds to the mean value of $H_{\mathrm{dep}}$ averaged over 10 measurements or more and the error bars show the standard deviation. In (b), the black lines are a linear fit of the data. Inset in (a): dependence of the resistance and of the sample temperature rise $\Delta T$ with the current for $T_{\mathrm{cryo}}=130\mathrm{K}$.