Magnetic anisotropy in thin films of Prussian blue analogues

TL;DR

This study investigates the magnetic anisotropy in thin and thick films and powders of a Prussian blue analogue, revealing that the anisotropy originates from magnetic domains and demagnetization effects rather than structural or g-tensor anisotropy.

Contribution

It demonstrates that magnetic anisotropy in these films is due to domain and demagnetization effects, not structural or g-tensor anisotropy, highlighting the importance of film growth protocol.

Findings

Anisotropy is not due to the solid support or g-tensor effects.

Magnetic domains and demagnetization factors explain the anisotropic response.

Film growth protocol influences the magnetic anisotropy.

Abstract

The magnetic anisotropy of thin (~ 200 nm) and thick (~ 2 $\mu$m) films and of polycrystalline (diameters ~ 60 nm) powders of the Prussian blue analogue Rb$_{0.7}$Ni$_{4.0}$[Cr(CN)$_6$]$_{2.9} \cdot n$H$_2$O, a ferromagnetic material with $T_c \sim 70$ K, have been investigated by magnetization, ESR at 50 GHz and 116 GHz, and variable-temperature x-ray diffraction (XRD). The origin of the anisotropic magnetic response cannot be attributed to the direct influence of the solid support, but the film growth protocol that preserves an organized two-dimensional film is important. In addition, the anisotropy does not arise from an anisotropic g-tensor nor from magneto-lattice variations above and below $T_c$. By considering effects due to magnetic domains and demagnetization factors, the analysis provides reasonable descriptions of the low and high field data, thereby identifying the origin of the magnetic anisotropy.