Positive Domain Wall Resistance of $180°$ Néel Walls in Co Thin Films

We measured the intrinsic domain wall resistance (DWR) of $180°$ Néel walls in a polycrystalline Co thin film deposited on top of a patterned antiferromagnetic CoO template. After field cooling through the CoO blocking temperature, exchange bias induces a spatially modulated coercivity of the Co film, resulting in a periodic domain pattern with $180°$ Néel walls. The intrinsic DWR is determined unambiguously by using rotating magnetic fields that result in a reversible creation and annihilation of the Néel walls. In contrast with earlier reports, the DWR is positive and in agreement with models based on the giant magnetoresistance mechanism. A reliable, quantitative determination of the DWR requires careful numerical evaluation of the anisotropic magnetoresistance effect.

Figure 1

(a) Schematic drawing of the patterned bilayer. A continuous Co film is deposited on top of $2\mu \mathrm{m}$ wide CoO stripes. After field cooling the Co film is locally exchange biased and the stripe domain pattern can be created by reversing the magnetic field. The color contrast and the dotted line in (b) represent the changing magnetization direction with respect to the current inside the Néel wall, which is obtained from micromagnetic simulations. The continuous line gives the corresponding calculated AMR resistivity inside the wall.

Figure 2

Magnetization (a) and magnetoresistance (b) at 5 K of the patterned $\mathrm{C}\mathrm{o}\mathrm{O}/\mathrm{C}\mathrm{o}$ bilayer for two consecutive hysteresis loops with the field parallel to the CoO stripes. The sample was cooled from room temperature in a field of 400 mT parallel to the stripes. The two-step behavior of the magnetization loop and the smaller peaks in the magnetoresistance confirm the presence of the stripe domain pattern.

Figure 3

Variation of the magnetoresistance (with respect to the resistance $R$ at 100 mT) when rotating a magnetic field with a magnitude of 16.9 mT in the plane of the patterned $\mathrm{C}\mathrm{o}\mathrm{O}/\mathrm{C}\mathrm{o}$. The bottom and the top axis refer to the bottom and the top curve, respectively. The labels (a)–(d) correspond to the diagrams in the upper panels. The artificial stripe domain pattern is created at an angle of $180°$ (c).