Controlling the switching field in nanomagnets by means of domain-engineered antiferromagnets

Using soft x-ray spectromicroscopy, we investigate the magnetic domain structure in embedded nanomagnets defined in $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ thin films and $\mathrm{LaFe}{\mathrm{O}}_3/\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ bilayers. We find that shape-controlled antiferromagnetic domain states give rise to a significant reduction of the switching field of the rectangular nanomagnets. This is discussed within the framework of competition between an intrinsic spin-flop coupling and shape anisotropy. The data demonstrates that shape effects in antiferromagnets may be used to control the magnetic properties in nanomagnets.

Figure 1

(a) XMLD-PEEM image of the boundary between a patterned and unpatterned region in a single-layer AF LFO thin film. We note the predominance of domains parallel to the patterned edges close to the boundary. (b) XMLD-PEEM (top) and XMCD-PEEM (bottom) images showing nanomagnets in the AF LFO and the FM LSMO layer, respectively. Edge-stabilized domains dominate the AF domain pattern, and the magnetization in the FM is governed by shape anisotropy. (c) Schematic of the collinear spin structure in the bilayer nanomagnets and the cross section of the embedded nanomagnets.

Figure 2

(a) XMCD-PEEM images of an array of more than 100 nominally identical nanomagnets defined in FM LSMO; (b) selected column of this array after initial uniform magnetization and subsequent applied magnetic field pulses of increasing magnitude in the opposite direction, for LSMO single-layer (top panel) and LFO/LSMO bilayer nanomagnets (bottom panel). The experimental geometry appears from the schematics on the left.

Figure 3

Percentage of switched nanomagnets in the measured ensemble as a function of the applied magnetic field pulse for nanomagnets defined in the LSMO single layer and the LFO/LSMO bilayer, respectively. The solid lines show numerical fits using the adopted model for magnetic switching of 100 nanomagnets. We note that although each magnet switches abruptly, there is a statistical spread in the switching field for the ensemble.

Figure 4

Schematic showing the effective anisotropy axes imposed on the FM layer: (a) shape anisotropy for the LSMO single layer and (b) shape anisotropy and interface coupling for the LFO/LSMO bilayer. (c) The angles defining the orientations of the external field ${\mathit{H}}_{\mathrm{ext}}$, the AF Néel vector $\mathit{L}$, and the FM magnetization $\mathit{M}$.