Single-domain shape anisotropy in near-macroscopic Ni$_{80}$Fe$_{20}$ thin-film rectangles

TL;DR

This study demonstrates that large, patterned Ni80Fe20 thin-film rectangles can exhibit single-domain-like shape anisotropy fields, challenging the notion that domain formation limits anisotropy effectiveness in larger ferromagnetic structures.

Contribution

The paper shows that controlled Ni80Fe20 thin-film rectangles larger than 10 μm can display shape anisotropy consistent with single-domain models, using fluxmetric anisotropy estimates.

Findings

Shape anisotropy fields match single-domain models in large rectangles.

Fluxmetric anisotropy estimate is superior to magnetometric form.

Large patterned films exhibit single-domain-like behavior.

Abstract

Shape anisotropy provides a simple mechanism to adjust the local bias field in patterned structures. It is well known that for ellipsoidal particles $<1$ $\mu$m in size, a quasi-single domain state can be realized with uniform anisotropy field. For larger patterned ferromagnetic thin-film elements, domain formation is thought to limit the effectiveness of shape anisotropy. In our work we show that very soft lithographically patterned Ni$_{80}$Fe$_{20}$ films with control of induced magnetic anisotropy can exhibit shape anisotropy fields in agreement with single-domain models, for both hysteresis loop measurements at low field and ferromagnetic resonance measurements at high field. We show the superiority of the fluxmetric form over the magnetometric form of anisotropy estimate for thin films with control dimensions from 10 $\mu$m to 150 $\mu$m and in-plane aspect ratios above 10.