Institute of Magnetism

Advances in nanotechnology and spintronics demand new nanomaterials with stable magnetoresistive (MR) properties. In this work, we investigated the temperature stability of MR properties in alloy thin films based on permalloy (Ni<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</inf>Fe<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</inf>) and copper. The samples were fabricated by electron-beam co-evaporation using two independent electron guns, followed by vacuum annealing to examine the effect of thermal treatment on their structural and MR properties. Transmission electron microscopy revealed that the structural-phase state remained stable over a wide composition range, both in the as-deposited state and after annealing up to 800 K. Magnetoresistance measurements showed that isothermal annealing at 700 K had no significant effect on the magnitude of giant magnetoresistance (GMR), and the magnetic field dependence of the magnetoresistance retained its isotropic character. These findings confirm the suitability of these films for thermally demanding spintronic applications.

The magnetically induced stresses in “Fe/Ni–Mn–Ga single crystalline particles/Fe” laminate composites have been studied depending on the thickness of the framing Fe foils and the distances between them. It evaluated the magnetically induced repulsive force between the two Fe foils which results in additional tensile stress of NiMnGa particles experimentally observed before. The presented calculation shows the way to improve the magnetostrain performance of laminate composite actuators.

Bloch lines are specific topological magnetic solitons, which can be present in domain walls (frequently called Bloch Walls) of biaxial ferromagnets; they are an element of an interesting “Bloch hierarchy” of topological solitons “Bloch walls–Bloch lines–Bloch points”. For a few decades, Bloch lines have been of interest for applications as possible information carriers for magnetic memory and logic devices. Here, we discuss the general properties of Bloch lines for the general model of two-sublattice ferrimagnets, with special attention to their dynamics. Effective equations for collective variables describing the motion of Bloch lines are constructed and analyzed. A universal behavior of these solitons for different levels of disbalance of sublattice spins is predicted and employed for the calculation of concrete characteristics like limit velocities, energy, effective masses, etc. It is found that Bloch lines in ferrimagnetic domain walls near the point of compensation of sublattice spin densities can move much faster than for conventional ferromagnets. The found dependence of Bloch line energy on its linear momentum exhibits a non-trivial element, an endpoint at some finite momentum value. This characteristic leads to the specific “explosive instability” leading to the abrupt change of soliton’s velocity accompanied by the intense radiation of spin waves.

We analytically solve the Landau-Lifshitz equations for the collective magnetization dynamics in a synthetic antiferromagnet (SAF) nanoparticle and uncover a regime of barrier-free switching under a short small-amplitude magnetic field pulse applied perpendicular to the SAF plane. We give examples of specific implementations for forming such low-power and ultra-fast switching pulses. For fully optical, resonant, barrier-free SAF switching we estimate the power per write operation to be ∼100 pJ, 10–100 times smaller than for conventional quasi-static rotation, which should be attractive for memory applications.

The structure and magnetic properties of epitaxial Heusler alloy films (Co2FeGe) deposited on MgO (100) substrates were investigated. Films of 60 nm thickness were prepared by magnetron co-sputtering at different substrate temperatures (TS), and those deposited at room temperature were later annealed at various temperatures (Ta). X-ray diffraction confirmed (001) [110] Co2FeGe || (001) [100] MgO epitaxial growth. A slight tetragonal distortion of the film cubic structure was found in all samples due to the tensile stress induced by the mismatch of the lattice parameters between Co2FeGe and the substrate. Improved quality of epitaxy and the formation of an atomically ordered L21 structure were observed for films processed at elevated temperatures. The values of magnetization increased with increasing TS and Ta. Ferromagnetic resonance (FMR) studies revealed 45° in-plane rotation of the easy anisotropy axis direction depending on the degree of the tetragonal distortion. The film annealed at Ta = 573 K possesses the minimal FMR linewidth and magnetic damping, while both these parameters increase for another TS and Ta. Overall, this study underscores the crucial role of thermal treatment in optimizing the magnetic properties of Co2FeGe films for potential spintronic and magnonic applications.