The interesting physics and potential memory technologies resulting from topologically protected spin textures such as skyrmions have prompted efforts to discover new material systems that can host these kinds of magnetic structures. Here, we use the highly tunable magnetic properties of amorphous Fe/Gd multilayer films to explore the magnetic properties that lead to dipole-stabilized skyrmions and skyrmion lattices that form from the competition of dipolar field and exchange energy. Using both real space imaging and reciprocal space scattering techniques, we determined the range of material properties and magnetic fields where skyrmions form. Micromagnetic modeling closely matches our observation of small skyrmion features (\ensuremath{\sim}50 to 70 nm) and suggests that these classes of skyrmions have a rich domain structure that is Bloch-like in the center of the film and more N\'eel-like towards each surface. Our results provide a pathway to engineer the formation and controllability of dipole skyrmion phases in a thin film geometry at different temperatures and magnetic fields.

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Tailoring magnetic energies to form dipole skyrmions and skyrmion lattices

The magnetic and structural properties of GdFe2 thin films prepared by electron beam coevaporation have been investigated. The measurements included magnetic resonance, magnetometer, the Mossbauer effect, x‐ray diffraction, and Auger analysis. Comparisons were made between the properties of the as‐deposited amorphous films and films annealed at various temperatures up to 500 °C, at which point crystallization is essentially complete. The measured magnetization for amorphous films was less than the magnetization measured in crystalline films at all temperatures. The magnetic moment of the Gd and Fe ions within their respective magnetic sublattices were determined to be 7.6 and 2.12μβ for crystalline GdFe2. The sublattice moments in the amorphous case do not change appreciably from the crystalline case. The sublattice g values were determined to be slightly temperature dependent below 77 K. The Landau‐Lifshitz magnetic damping parameter was determined to be ∼1×107 and 2×107 Hz for amorphous and crystalline ...

Magnetic properties of amorphous and crystalline GdFe2

We present the results of the magnetic measurements on (GdxY1−x)Fe2 compounds between 4.2 and 1300 K. For x≳0 typical magnetization curves characteristic of ferrimagnetic ordering are evidenced. The reciprocal susceptibility follows a Neel‐type relation. The composition dependence of the magnetic interactions in the system is analyzed. The iron moment scales linearly with the exchange field acting on Fe atoms. The correlation between the Fe57 hyperfine field and the electronic moment MFe at the iron site in a number of rare‐earth (yttrium) compounds is presented. A simple linear relation is found. Based on the above data a comparison between the thermal variation of iron magntization, calculated using the Neel model, and that deduced from the hyperfine field is made. The data evidence that the molecular field model describes rather well the magnetic behavior of these systems. The results of ferromagnetic‐resonance measurements in X and K bands are presented. The data are analyzed using the Vangsness relat...

On the magnetic behavior of iron in ternary gadolinium‐yttrium compounds

Measurements of ferromagnetic resonance (FMR) in both in-plane (H‖) and out-of-plane (H⊥) magnetic field configurations have been performed on a series of epitaxial (La0.7Ca0.3)1−xMn1+xO3 films. The FMR linewidths have a local maximum near the Curie point and increase continuously at low temperatures. The effective anisotropy of the films has the easy-plane character. The angular dependences of Hres were found to be in reasonable agreement with the theoretical ones, taking into account the second- and fourth-order terms of the magnetic anisotropy energy. A reasonable agreement between ΔHres(α) and Bloch type dissipation was obtained only for deviations of the external field from the normal to the film plane up to α=20°. From the temperature and angular dependences of the FMR spectra, the main magnetic parameters such as the effective magnetization, effective field Heff, anisotropy field HA2, and FMR linewidth were estimated.

Ferromagnetic resonance in (La0.7Ca0.3)1−xMn1+xO3 films

We have studied the magnetic properties of the SURMOF-2 series of metal–organic frameworks (MOFs). Contrary to bulk MOF-2 crystals, where Cu2+ ions form paddlewheels and are antiferromagnetically coupled, in this case the Cu2+ ions are connected via carboxylate groups in a zipper-like fashion. This unusual coupling of the spin 1/2 ions within the resulting one-dimensional chains is found to stabilize a low-temperature, ferromagnetic (FM) phase. In contrast to other ordered 1D systems, no strong magnetic fields are needed to induce the ferromagnetism. The magnetic coupling constants describing the interaction between the individual metal ions have been determined in SQUID experiments. They are fully consistent with the results of ab initio DFT electronic structure calculations. The theoretical results allow the unusual magnetic behavior of this exotic, yet easy-to-fabricate, material to be described in a detailed fashion.

P. Lubitz

Papers

Microwave magnetic properties of gadolinium-iron films

Ferromagnetic resonance in an ultrathin manganate film