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Abstract: The collective precession of magnetization manifests itself as magnon modes. These modes are governed by complex-valued vectorial eigenfunctions, which have remained experimentally challenging to observe. Here we introduce X-ray magnetic vector chronoscopy (XMVC), a time-resolved resonant scattering method that reconstructs the full magnetization dynamics with angular resolution of 0.1° (±0.01°). Applied to a synthetic antiferromagnetic multilayer (Si/NiFe (8 nm)/Ru (0.8 nm)/CoFeB (5.5 nm)), XMVC enables magnon state tomography, by directly measuring the nanoscale vectorial eigenfunctions of hybridized modes arising from magnon–magnon coupling. This approach provides full access to the system’s non-Hermitian Hamiltonian, revealing the complex-valued coupling strengths and non-orthogonal eigenbases. These results establish XMVC as an experimental platform for studying nanoscale spin systems by extracting the eigenfunctions of the system.

Open Access

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Abstract: Chemical disorder in compositionally complex perovskite oxides generates a broad distribution of exchange pathways and spin states, but the microscopic origin and spatial homogeneity of the resulting magnetic phases remain debated. Here, we tune the Mn fraction (x = 0.2–0.6) in epitaxial La(Cr, Mn, Fe, Co, Ni)O3 thin films and resolve the coupled evolution of valence, spin state, and magnetism using element-specific x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD). Mn enrichment drives an internal redistribution of charge, in which Mn evolves toward a Mn3+-rich mixed valence, while Co converts from predominantly Co3+ to high-spin Co2+. This valence/spin-state coupling amplifies the Mn- and Co-derived ferromagnetic response by nearly an order of magnitude while increasing the magnetic onset temperature to at least 250 K, whereas Fe and Cr remain essentially trivalent with weak dichroism. Depth-resolved low-energy muon spin spectroscopy (LE-μSR) shows magnetic homogeneity through the film thickness, with a secondary relaxation maximum near 25 K indicating a low-temperature dynamical crossover consistent with frustrated magnetism in a strongly disordered spin lattice.

Open Access

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Abstract: Magnetocrystalline anisotropy is a key parameter governing the performance of magnetic nanoparticles in many applications. However, disentangling its intrinsic contribution from other sources of effective anisotropy, such as surface effects, dipolar interactions or shape anisotropy, remains highly challenging. Here, we report a novel approach to qualitatively estimate the magnetocrystalline anisotropy of two CoxFe3−xO4 nanoparticles with different Co contents (x = 0.11 and 0.61) using polarized neutron powder diffraction (PNPD). The off-diagonal elements of the susceptibility tensors and degree of asymmetry of the magnetization ellipsoids obtained from the PNPD refinements reveal that the sample with x = 0.61 presents a larger magnetocrystalline anisotropy than the sample with x = 0.11, which is consistent with the effective anisotropy derived from magnetometry. Moreover, comparison of the PNPD-derived magnetization ellipsoids across materials with varying anisotropies confirms the direct relationship between the ellipsoid asymmetry and magnetocrystalline anisotropy. These findings establish PNPD as a powerful tool for qualitatively probing intrinsic anisotropies in nanoparticle systems, paving the way for the rational design and optimization of magnetic nanoparticles for advanced applications.

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Abstract: he pyrochlore vanadates are compelling candidates for next-generation dissipationless devices. and are ferromagnetic insulators (T 70 K) that are believed to exhibit the magnon Hall effect and are expected to host topological magnons. Their completely dissipationless magnon edge states could be harnessed to realize low-power information transport in spintronic or magnonic devices. As a crucial step in the realization of devices, we synthesize the first thin films of pyrochlore on isostructural substrates and explore the evolution of their magnetic properties down to the ultrathin limit. All films are insulating ferromagnets with transition temperatures of up to the bulk value (T 68 K) that decrease with thickness according to finite-size effects. Our films also exhibit a change in anisotropy from in-plane to out-of-plane easy axis coincident with the development of partial strain relaxation and nonzero magnetic hysteresis in an applied field. This evolution demonstrates the impact of strain on magnetic anisotropy and paves the way to tunable magnon topology.

Open Access

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Abstract: Cobalt ferrite nanoparticles are a benchmark among low-to-medium energy alternatives to rare-earth permanent magnets, although their intrinsic behavior is often obscured by surface disorder, finite-size effects, and superparamagnetic relaxation. Here, we overcome these limitations by synthesizing large, highly crystalline cobalt-doped ferrite nanoparticles (≈ 25 nm), which remain blocked at room temperature and thus provide a clean platform to disentangle the fundamental role of cobalt in the spinel lattice. By systematically varying the cobalt content, we reveal a complex interplay between cation distribution, oxygen vacancy formation, and magnetic response. Structural and compositional analysis confirms predominant Co2+ occupancy at octahedral sites, accompanied by a redistribution of Fe2+/Fe3+ and non-linear oxygen vacancy generation. We find that while saturation magnetization is largely governed by defect chemistry, the coercivity and effective anisotropy are primarily controlled by cobalt incorporation and saturate at intermediate compositions. In contrast, thermomagnetic analysis reveals an anomalous evolution of magnetization at intermediate temperatures for specific cobalt contents. This behavior is consistent with a change in the anisotropy landscape, suggestive of a growing contribution from higher-order anisotropy terms, rather than a simple uniform increase in magnetocrystalline anisotropy. These results indicate that cobalt doping tunes the balance between different anisotropy contributions in a composition- and temperature-dependent manner. Overall, our findings highlight the subtle interplay between cation distribution, anisotropy landscape, and thermal stability in spinel ferrites, providing fundamental insight for the design of high-coercivity rare-earth-free nanomagnets.