An in-depth analysis of Zn/Al-doped nickel ferrites grown by reactive magnetron sputtering is relevant due to their promising characteristics for applications in spintronics. The material is insulating and ferromagnetic at room temperature with an additional low magnetic damping. By studying the complex interplay between strain and cation distribution their impact on the magnetic properties, i.e., anisotropy, damping, and g-factor is unravelled. In particular, a strong influence of the lattice site occupation of Ni 2+ Td and cation coordination of Fe 2+ Oh on the intrinsic damping is found. Furthermore, the critical role of the incorporation of Zn 2+ and Al 3+ is evidenced by comparison to a sample of altered composition. Specifically, the dopant Zn 2+ is evidenced as a tuning factor for Ni 2+ Td and therefore unquenched orbital moment directly controlling the g-factor. A strain-independent reduction of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.

A non-standing character of directly imaged spin-waves in confined micron-sized ultrathin permalloy (Ni 80 Fe 20 ) structures is reported along with evidence of the possibility to alter the observed state by modifications to the sample geometry. Using micromagnetic simulations the presence of the spin-wave modes excited in the permalloy stripes along with the quasi-uniform modes were calculated. The predicted spin-waves were imaged in direct space using time resolved scanning transmission X-ray microscopy, combined with a ferromagnetic resonance excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing character of the spin-waves. Also it was shown by micromagnetic simulations and confirmed with STXM-FMR results that the observed character of the spin-waves can be influenced by the local magnetic fields in different sample geometries.

Using a time-resolved detection scheme in scanning transmission X-ray microscopy (STXM), we measured element resolved ferromagnetic resonance (FMR) at microwave frequencies up to 10 GHz and a spatial resolution down to 20 nm at two different synchrotrons. We present different methods to separate the contribution of the background from the dynamic magnetic contrast based on the X-ray magnetic circular dichroism (XMCD) effect. The relative phase between the GHz microwave excitation and the X-ray pulses generated by the synchrotron, as well as the opening angle of the precession at FMR can be quantified. A detailed analysis for homogeneous and inhomogeneous magnetic excitations demonstrates that the dynamic contrast indeed behaves as the usual XMCD effect. The dynamic magnetic contrast in time-resolved STXM has the potential be a powerful tool to study the linear and nonlinear, magnetic excitations in magnetic micro- and nano-structures with unique spatial-temporal resolution in combination with element selectivity.

Spin pumping in a ferromagnet-nonferromagnet heterostructure is directly imaged with spatial resolution as well as element selectivity. The time-resolved detection in scanning transmission x-ray microscopy allows us to directly probe the spatial extent of the ac spin polarization in Co-doped ZnO, which is generated by spin pumping from an adjacent permalloy microstrip. Comparing the relative phases of the dynamic magnetization component of the two constituents is possible and found to be close to antiphase. The correlation between the distribution of the magnetic excitation in the permalloy and the Co-doped ZnO reveals that laterally there is no one-to-one correlation. The observed distribution is rather complex, but integrating over larger areas demonstrates that the spin polarization in the nonferromagnet extends laterally beyond the region of the ferromagnetic microstrip. Therefore, the observations are better explained by a local spin pumping efficiency and a lateral propagation of the ac spin polarization in the nonferromagnet over the range of a few micrometers.

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