Domain structure of epitaxial Co films with perpendicular anisotropy

TL;DR

This study investigates the structural and magnetic properties of epitaxial Co films with perpendicular anisotropy, analyzing domain structures and the transition from in-plane to out-of-plane magnetization as a function of film thickness.

Contribution

It provides detailed experimental insights into the domain structures and critical thickness for magnetization reorientation in epitaxial Co films, highlighting discrepancies with existing models.

Findings

Perpendicular anisotropy reaches that of single crystal hcp-Co.

Critical thickness for domain transition identified.

Discrepancies with existing domain models at small thicknesses.

Abstract

Epitaxial hcp Cobalt films with pronounced c-axis texture have been prepared by pulsed lased deposition (PLD) either directly onto Al2O3 (0001) single crystal substrates or with an intermediate Ruthenium buffer layer. The crystal structure and epitaxial growth relation was studied by XRD, pole figure measurements and reciprocal space mapping. Detailed VSM analysis shows that the perpendicular anisotropy of these highly textured Co films reaches the magnetocrystalline anisotropy of hcp-Co single crystal material. Films were prepared with thickness t of 20 nm < t < 100 nm to study the crossover from in-plane magnetization to out-of-plane magnetization in detail. The analysis of the periodic domain pattern observed by magnetic force microscopy allows to determine the critical minimum thickness below which the domains adopt a pure in-plane orientation. Above the critical thickness the width of the stripe domains is evaluated as a function of the film thickness and compared with domain theory. Especially the discrepancies at smallest film thicknesses show that the system is in an intermediate state between in-plane and out-of-plane domains, which is not described by existing analytical domain models.