Interplay between magnetic domain patterning and anisotropic magnetoresistance probed by magneto-optics

We study the correlation between the magnetic reversal and the anisotropic magnetoresistance (AMR) response in magnetic hybrid structures that were created by local modification of magnetic properties induced by ion implantation. The stripe pattern has been investigated simultaneously by dual-wavelength Kerr microscopy and magnetoresistance measurements. We observe that the switching of the stripe pattern introduces an additional AMR maximum. The domain wall in between the stripes provides a positive resistance contribution, whereas domains at the stripe edges lead to an asymmetric AMR response. A method for calculating the AMR response from the quantitative Kerr micrographs is demonstrated that allows the reconstruction of the AMR value within a region of interest only.

Figure 1

(a) VSM measurements with the field applied parallel to the induced anisotropy axis for the nonimplanted film (black curve) and implanted film (blue curve). (b) Magnetization with external field applied parallel to the induced anisotropy (black curve) and perpendicular to it (green curve).

Figure 2

Sketch of the four different sample layouts. The stripe width is given in µm. Black (white) color represents implanted (nonimplanted) stripes. The double headed arrow denotes the induced anisotropy axis.

Figure 3

$x$ component of $M$ perpendicular to the main stripe axes (green squares) and relative resistance change (orange squares) as a function of applied field sample with $w=20\mu \mathrm{m}|15\mu \mathrm{m}$ (implanted |  nonimplanted) stripes at ${\phi }_H=0^{\circ }$. The field (current) direction is denoted by a black (dashed red) arrow. (a)–(c) Corresponding domain images taken at field values marked with dotted lines in the upper panel. The color code denotes the magnetization direction. Black (white) rectangles mark implanted (nonimplanted) stripes. Note that only one field sweep direction (from negative to positive field) value is shown for the images.

Figure 4

$y$ component of $M$ (along stripe length) (black squares) and relative resistance change (orange squares) as a function of applied field for a sample with $w=15\mu \mathrm{m}|20\mu \mathrm{m}$ (implanted |  nonimplanted) stripes at ${\phi }_H={135}^{\circ }$. $R_s$ is the resistance of the sample measured at magnetic saturation in ${\phi }_H={135}^{\circ }$ direction. The field (current) direction is denoted by black (dashed red) arrows. (a)–(c) Corresponding domain images taken at field values marked with dotted lines in the upper panel. The color code denotes the magnetization direction. Black (white) rectangles mark implanted (nonimplanted) stripes. Only one field sweep direction (from negative to positive field) value is shown for the images.

Figure 5

$y$ component of $M$ (along stripe length) (black squares) and relative resistance change (orange squares) as a function of the applied field for sample with $w=20\mu \mathrm{m}|15\mu \mathrm{m}$ (implanted |  nonimplanted) stripes at ${\phi }_H={135}^{\circ }$. The field (current) direction is denoted by a black (dashed red) arrow. (a)–(d) Corresponding domain images taken at field values marked by dotted lines in the upper panel. Black (white) rectangles mark implanted (nonimplanted) stripes. Only one field sweep direction from negative to positive field values is shown. The inset shows the measurements of the $M$ component the along stripe length (black line) and relative resistance change (orange line) when the current is applied parallel to the stripe axis. $R_s$ is the resistance of the sample measured at saturation for the chosen field direction.

Figure 6

Measurement of the AMR at different field angles $\phi$ for (a) a permalloy film and (b) a stripe sample with $w=16\mu \mathrm{m}|16\mu \mathrm{m}$ (implanted |  nonimplanted) stripes. (c) Dependence of the height of the extra peak at the interface on the sum of implanted and nonimplanted stripe width ($w_{\mathrm{imp}}+w_{\mathrm{non}\mathrm{imp}}$).

Figure 7

AMR measurements on sample with $w=30\mu \mathrm{m}|20\mu \mathrm{m}$ $\left(\mathrm{implanted}\right|\mathrm{nonimplanted})$ stripes and ${\phi }_H=0^{\circ }$. $R_s$ is the resistance of the sample measured at magnetic saturation in ${\phi }_H=0^{\circ }$ direction.

Figure 8

Comparison of directly measured AMR and AMR calculated from Kerr images for composite stripe structures of series 4 with (a) $w=8$ µm stripes and ${\phi }_H=0^{\circ }$ and (b) $w=2$ µm stripes and ${\phi }_H={90}^{\circ }$.

Figure 9

Comparison of calculated AMR composite stripe structures (series 4). (a) Influence of stripe orientation for $w=8$ µm and ${\phi }_H=0^{\circ }$ and (b) influence of implantation for $w=2$ µm and ${\phi }_H=0^{\circ }$.