Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites

An in-depth analysis of Zn/Al doped nickel ferrite with a nominal composition of Ni$_\text{0.65}$Zn$_\text{0.35}$Al$_\text{0.8}$Fe$_\text{1.2}$O$_\text{4}$ was conducted to gain insight into the magnetic properties interesting for applications in spintronics. The material is insulating, ferromagnetic at room temperature and has a low magnetic damping with additional strong magneto-elastic coupling. A growth optimisation for reactive magnetron sputtering is performed and the sample system is analysed for crystal structure, chemical composition and static as well as dynamic magnetic properties. Thus a correlation between strain, cation distribution, magneto-crystalline anisotropy and damping is evidenced. XMCD and XMCD(H) measurements at the L$_{3,2}$ edge of Ni and Fe are performed to complement integral SQUID magnetometry and identify their magnetic contributions to the hysteresis. In particular, a strong influence of the lattice site occupation of Ni$^{2+}_{\text{Td}}$ and cation coordination of Fe$^{2+}_{\text{Oh}}$ on the intrinsic damping is found. Furthermore, the vital role of the incorporation of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a control sample of slightly altered nominal stoichiometry. A strain-independent improvement of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.