Epitaxial CoRu-alloy films with (1010) surface orientation and varying stoichiometry have been grown at room temperature. In order to achieve good epitaxy independent from the alloy composition, we have devised an underlayer sequence, which utilized a CrRu-alloy film as template layer with individually optimized composition. All alloys in the composition range of 0–30 at. % Ru content exhibit hcp structure and thus uniaxial magneto-crystalline anisotropy. We observe an almost linear decrease of the saturation magnetization and Curie temperature with increasing Ru content. However, the magneto-crystalline anisotropy shows a non-monotonous behavior with a maximum near 15% Ru.

Controlling material properties by modulating the crystalline structure has been attempted using various techniques, e.g., hydrostatic pressure, chemical pressure, and epitaxy. These techniques succeed to improve properties and achieve desired functionalities by changing the unit cell in all dimensions. In order to obtain a more detailed understanding on the relation between the crystal lattice and material properties, it is desirable to investigate the influence of a smaller number of parameters. Here, we utilize the combination of chemical pressure and epitaxy to modify a single lattice parameter of the multiferroic orthorhombic RMnO3 (R = rare-earth; o-RMnO3) system. By growing a series of o-RMnO3 (R = Gd -Lu) films coherently on (010)oriented YAlO3 substrates, the influence of chemical pressure is reflected only along the b-axis.Thus, a series of o-RMnO3 with a ~ 5.18 Å, 5.77 Å < b < 5.98 Å, and c ~ 7.37 Å were obtained.Raman spectra analysis reveals that the change of the b-axis parameter induces a shift of the oxygen in the nominally "fixed" ca-plane. Their ferroelectric ground state is independent on the b-axis parameter showing polarization of ~ 1 µC cm -2 along the a-axis for the above-mentioned range, except for b ~ 5.94 Å which corresponds to TbMnO3 showing ~ 2 µC cm -2 . This result implies that multiferroic order of o-RMnO3 is almost robust against the b-axis parameter provided that the dimension of the ca-plane is fixed to 7.37 Å × 5.18 Å.

We study the magnetic properties of weakly disordered Co films with in-plane uniaxial magnetocrystalline\ud anisotropy. The growth sequence used allowed the controlled introduction of grain orientation disorder. Above\ud a threshold disorder level, we observe an anomalous magnetic reversal near the nominal hard axis; while the behavior in all other field orientations is barely affected.Atwo-grain model explains the anomaly as the occurrence of nonuniform magnetization states near the hard axis, a fact that is experimentally confirmed by Kerr microscopy

Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core. The control of the polarization of this core and its gyration is key to the utilization of vortices in technological applications. So far polarization control has been achieved in single-material structures using magnetic fields, spin-polarized currents or spin waves. Here we demonstrate local control of the vortex core orientation in hybrid structures where the vortex in an in-plane Permalloy film coexists with out-of-plane maze domains in a Co/Pd multilayer. The vortex core reverses its polarization on crossing a maze domain boundary. This reversal is mediated by a pair of magnetic singularities, known as Bloch points, and leads to the transient formation of a three-dimensional magnetization structure: a Bloch core. The interaction between vortex and domain wall thus acts as a nanoscale switch for the vortex core polarization.