Focused ion beam irradiation of metastable Fe78Ni22 thin films grown on Cu(100) substrates is used to create ferromagnetic, body-centered-cubic patterns embedded into paramagnetic, face-centeredcubic surrounding. The structural and magnetic phase transformation can be controlled by varying parameters of the transforming gallium ion beam. The focused ion beam parameters as ion dose, number of scans, and scanning direction can be used not only to control a degree of transformation, but also to change the otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy along specific crystallographic direction. This change is associated with a preferred growth of specific crystallographic domains. The possibility to create magnetic patterns with continuous magnetization transitions and at the same time to create patterns with periodical changes in magnetic anisotropy makes this system an ideal candidate for rapid prototyping of a large variety of nanostructured samples. Namely spin-wave waveguides and magnonic crystals can be easily combined into complex devices in a single fabrication step.Direct writing of magnetic patterns by focused ion beam (FIB) irradiation 1 presents a favorable alternative to the conventional lithography approaches. It removes the need for further processing of the specimen and allows for a rapid prototyping of a large variety of nanostructured samples. Since the pioneering work of Chappert et al. 2 , many different approaches to ion-beam-induced magnetic patterning have been studied, including modification of magnetic anisotropies 2 , coercivity, exchange bias 3 or the magnetization of the

Metastable Fe78Ni22 thin films are excellent candidates for focused ion beam direct writing of magnonic structures due to their favorable magnetic properties. The focused ion beam transforms the originally nonmagnetic fcc phase into the ferromagnetic bcc phase with an additional control over the direction of uniaxial magnetic in-plane anisotropy and the saturation magnetization. The induced anisotropy allows to stabilize transverse direction of magnetization in narrow waveguides. Therefore, it is possible to propagate spin waves in these waveguides in the favorable Demon-Eshbach geometry without the presence of any external magnetic field. Nowadays, the vibrant field of magnonics stands on the edge between development of elementary building blocks of magnonic circuitry and envisioned all magnon on-chip devices [1,2]. The magnonic devices, utilizing physics of spin waves, are recognized to have potential in information processing in the frequency range from gigahertz to terahertz. High frequencies, together with low energy of elementary excitations render the magnonic devices suitable for beyond-CMOS computational technologies. Many concepts of future devices used for steering and manipulating spin waves have been presented recently [3][4][5][6]. To allow further advances in this field, new types of materials possessing additional means of control over their magnetic properties together with good spin wave propagation are needed.Here we show, that magnonic waveguides allowing for fast spin-wave propagation at zero magnetic field can be directly written into metastable Fe78Ni22 thin films by focused ion beam (FIB). The local dose and scanning strategy controls both the saturation magnetization and the magnetocrystalline anisotropy (direction, type and strength) of irradiated areas. The unique possibilities of this material system allow to overcome the shape anisotropy of long magnonic waveguides and stabilize

Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the transformable region is presented.

Spin waves have the potential to be used as a next-generation platform for data transfer and processing as they can reach wavelengths in the nanometer range and frequencies in the terahertz range. To realize a spin-wave device, it is essential to be able to manipulate the amplitude as well as the phase of spin waves. Several theoretical and recent experimental works have also shown that the spin-wave phase can be manipulated by the transmission through a domain wall (DW). Here, we study propagation of spin waves through a DW by means of micro-focused Brillouin light scattering microscopy (μBLS). The 2D spin-wave intensity maps reveal that spin-wave transmission through a Néel DW is influenced by a topologically enforced circular Bloch line in the DW center and that the propagation regime depends on the spin-wave frequency. In the first regime, two spin-wave beams propagating around the circular Bloch line are formed, whereas in the second regime, spin waves propagate in a single central beam through the circular Bloch line. Phase-resolved μBLS measurements reveal a phase shift upon transmission through the domain wall for both regimes. Micromagnetic modeling of the transmitted spin waves unveils a distortion of their phase fronts, which needs to be taken into account when interpreting the measurements and designing potential devices. Moreover, we show that, by means of micromagnetic simulations, an external magnetic field can be used to move the circular Bloch line within the DW and to manipulate spin-wave propagation.