Micromagnetism and magnetotransport properties of micron-sized epitaxial $\mathrm{Cr}{\mathrm{O}}_2\left(100\right)$ wires

We report a detailed study of the magnetic domain configurations and the magnetization reversal in epitaxial $\mathrm{Cr}{\mathrm{O}}_2\left(100\right)$ wires ($0.5–5\mu \mathrm{m}$ widths) patterned along different crystallographic directions. Magnetic force microscopy imaging in zero field reveals single domain states for wires fabricated along the magnetic easy axis, while wires perpendicular to the magnetic easy axis exhibit a stripe domain configuration. The behavior in an applied field and the switching of the magnetization is probed by magnetoresistance (MR) measurements. Depending on the orientation of the wire with respect to the easy and hard magnetocrystalline anisotropy axes and the field direction, distinctly different reversal modes are observed including inhomogeneous magnetization configurations. These modes and configurations can be explained taking into account the interplay between the different anisotropy terms. MR measurements at variable temperatures demonstrate that the low temperature MR response is dominated by intergrain-tunneling magnetoresistance, while at elevated temperatures it is superseded by the anisotropic MR.

Figure 1

SEM image of a $\mathrm{Cr}{\mathrm{O}}_2$ transport structure consisting of the main wire connected to two contact pads (A and B) and four additional contact leads (1–4) with contact pads (not shown).

Figure 2

MOKE hysteresis loops of a $\mathrm{Cr}{\mathrm{O}}_2\left(100\right)$ film with the magnetic field applied along the [001] direction (magnetic easy axis) and along the [010] direction (magnetic hard axis).

Figure 3

(Color online) AFM [(a) and (d)] and MFM images [(b) and (e)] of $2\mu \mathrm{m}$ wide $\mathrm{Cr}{\mathrm{O}}_2$ wires fabricated along the [001] direction [(a) and (b)] and the [010] direction [(d) and (e)]. Schematics (c) and (f) represent the MFM contrast formation due to the stray fields for both configurations.

Figure 4

Rotational scans measured on the $2\mu \mathrm{m}$ wide easy structure [(a) and (b)] as well on the $2\mu \mathrm{m}$ wide hard structure [(c) and (d)] at $4.2\mathrm{K}$ (left-hand panels) and at $190\mathrm{K}$ (right-hand panels). The direction of the magnetic field (see inset in the center) is defined as 0° (or 180°) and 90° (or 270°), respectively, if it is applied parallel and perpendicular to the [001] direction, i.e., the magnetic easy axis, of the $\mathrm{Cr}{\mathrm{O}}_2$ film. In all plots the orientation of the magnetization of the $\mathrm{Cr}{\mathrm{O}}_2$ grains is shown for minimum and maximum resistance.

Figure 5

The field dependence of the MR of the $2\mu \mathrm{m}$ wide easy structure with the magnetic field applied parallel (a) and perpendicular (b) to the [001] direction measured at $4.2\mathrm{K}$. Schematics at the upper side of each plot represent different magnetization configurations during the magnetization reversal process.

Figure 6

The compensation field $\left(B_{\mathit{comp}}\right)$, i.e., the position of the MR maxima, is shown as a function of the $\mathrm{Cr}{\mathrm{O}}_2$ wire width. The inset shows the MR ratio of a $\mathrm{Cr}{\mathrm{O}}_2$ easy structure as a function of external magnetic field which is applied perpendicular to the [001] direction of $\mathrm{Cr}{\mathrm{O}}_2$. The position of the MR maximum is marked as $B_{\mathit{comp}}$.

Figure 7

(a) The field dependence of the MR of the $2\mu \mathrm{m}$ wide hard structure measured at $4.2\mathrm{K}$ with the magnetic field applied parallel to the [001] direction. In (b) the compensation field $\left(B_{\mathit{comp}}\right)$ as a function of the $\mathrm{Cr}{\mathrm{O}}_2$ wire width is presented. The inset shows the MR of a $\mathrm{Cr}{\mathrm{O}}_2$ hard structure as a function of external magnetic field which is applied parallel to the [001] direction with the position of the MR maximum marked as $B_{\mathit{comp}}$. (c) The field dependence of the MR ratio of the $2\mu \mathrm{m}$ wide $\mathrm{Cr}{\mathrm{O}}_2$ hard structure with the magnetic field applied perpendicular to the [001] direction. (d) A zoom-in on the field dependence of the MR ratio of the same $2\mu \mathrm{m}$ wide hard structure with the magnetic field applied perpendicular to the [001] direction of $\mathrm{Cr}{\mathrm{O}}_2$. Schematics at the upper side of the plots (a), (c), and (d) represent different magnetization configurations during the magnetization reversal process.

Figure 8

Minor hysteresis loops measured at $4.2\mathrm{K}$ with increasing magnetic field amplitude $\left(B_{\mathit{max}}\right)$ on the $2\mu \mathrm{m}$ wide hard structure with the magnetic field applied perpendicular to the [001] direction of $\mathrm{Cr}{\mathrm{O}}_2$.