Diffractive magneto-optics, magnetic interactions, and reversal mechanisms in $\mathrm{Co}$ microsquare arrays

The magneto-optical properties of $\mathrm{Co}$ microsquare—$2\mu \mathrm{m}$ edge—arrays have been investigated for different interelement separations, from 0.2 to $2.0\mu \mathrm{m}$. The magneto-optical response is measured both at reflected and diffracted beams, and it is compared with the results of a model that uses micromagnetic simulations and optical diffraction theory to calculate the magneto-optical response for different diffracted spots. A satisfactory agreement between the experiments and the predictions from the combined micromagnetic and optical diffraction models allows the interpretation of the experimental data and provides a way to analyze and understand the physical meaning of the magneto-optic diffracted signal. The comparison of this diffracted magneto-optical experimental data with predictions from simple reversal models allows us to monitor different element magnetization reversal mechanisms as the separation between elements in the array varies.

Figure 1

Magneto-optic setup for tile array measurements.

Figure 2

Hysteresis loops, both for the zeroth order (reflected) and first $X$ and $Y$ diffracted orders, for arrays of $2\mu \mathrm{m}$ separated by $0.2\mu \mathrm{m}$, $0.5\mu \mathrm{m}$, $1.0\mu \mathrm{m}$, and $2.0\mu \mathrm{m}$ with an external field $H$ parallel to the $\mathrm{Co}$ uniaxial anisotropy easy axis.

Figure 3

Hysteresis loops, both for the zeroth order (reflected) and first $X$ and $Y$ diffracted orders, for arrays of $2\mu \mathrm{m}$ separated by $0.2\mu \mathrm{m}$, $0.5\mu \mathrm{m}$, $1.0\mu \mathrm{m}$, and $2.0\mu \mathrm{m}$ with an external field $H$ parallel to the $\mathrm{Co}$ uniaxial anisotropy hard axis.

Figure 4

Micromagnetic simulations and the expected MO dependencies in the first diffraction orders calculated using conventional optical diffraction theory for arrays of $2\mu \mathrm{m}$ separated by $0.2\mu \mathrm{m}$, $0.5\mu \mathrm{m}$, $1.0\mu \mathrm{m}$, and $2.0\mu \mathrm{m}$ with $H$ parallel to the $\mathrm{Co}$ uniaxial anisotropy easy axis.

Figure 5

Magnetization distribution in a single square element of the array for different values of the external field $H$. Only $m_y$, which corresponds to the transversal Kerr effect signal, is displayed in color code.

Figure 6

Saturation field vs intertile distance.

Figure 7

Matching of the weighting factor for the diffracted $1X$ signal for (a) $a$ and (b) $a∕10$ intertile distances.

Figure 8

Diffracted signals $1X$ and $1Y$ vs magnetization for different inversion processes: (a) propagation of a single $180°$ domain wall parallel to the applied field, (b) propagation of two $180°$ domain walls parallel to the applied field, (c) coherent rotation of the magnetization, (d) $S$ state with domain walls situated at 1/6 square length of the edge, (e) $C$ state with domain walls situated at 1/6 square length of the edge, (f) vortex displacement along the $X$ axis, (g) two consecutive propagations of a single $90°$ domain wall, (h) two consecutive propagations of two simultaneous $90°$ domain walls, (i) rotation at the center of the element is followed by a rotation at the borders.

Figure 9

Experimental first order diffracted MO signal vs average magnetization for different interelement (from 0.2 to $2\mu \mathrm{m}$) separations. Data are shown when the field is applied both along the easy and the hard $\mathrm{Co}$ axes and parallel to the $2\mu \mathrm{m}$ $\mathrm{Co}$ square element.