We have determined the magnetic structures of single-crystal thin-films of IrMn3 for the crystallographic phases of chemically-ordered L12, and for chemically-disordered face-centred-cubic, which is the phase typically chosen for information-storage devices. For the chemically-ordered L12 thin-film, we find the same triangular magnetic structure as reported for the bulk material. We determine the magnetic structure of the chemically-disordered face-centred-cubic alloy for the first time, which differs from theoretical predictions, with magnetic moments tilted away from the crystal diagonals towards the face-planes. We study the influence of these two antiferromagnetic structures on the exchange-bias properties of an epitaxial body-centred-cubic Fe layer showing that magnetization reversal mechanism and bias-field in the ferromagnetic layer is altered significantly. We report a change of reversal mechanism from in-plane nucleation of 90° domain-walls when coupled to the newly reported cubic structure towards a rotational process, including an out-of-plane magnetization component when coupled to the L12 triangular structure.

Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures 1, 2 . While they are commonly portrayed as two dimensional objects, in reality magnetic skyrmions are thought to exist as elongated, tube-like objects extending through the thickness of the sample 3, 4 . The study of this skyrmion tube (SkT) state is highly relevant for investigating skyrmion metastability 5 and for implementation in recently proposed magnonic computing 6 . However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the first real-space observation of skyrmion tubes in a lamella of FeGe using resonant magnetic x-ray imaging and comparative micromagnetic simulations, confirming their extended structure.The formation of these structures at the edge of the sample highlights the importance of confinement and edge effects in the stabilisation of the SkT state, opening the door to further investigations into this unexplored dimension of the skyrmion spin texture.Skyrmion states are typically stabilised by the interplay of the ferromagnetic exchange and Zeeman energies with the Dzyalohsinskii-Moriya Interaction (DMI) 7 . In ferromagnet/heavy metal multilayer thin films, interfacial DMI is induced by symmetry-breaking spin-orbit coupling at the interface between the layers, leading to the formation of Néel-type skyrmions [8][9][10] . Bulk DMI, arising due to the lack of centrosymmetry in the underlying crystal lattice, is responsible for the formation of Bloch-type skyrmions in a range of chiral ferromagnets [11][12][13][14][15] . In crystals of these bulk materials the skyrmion state is typically only at equilibrium in a limited range of applied magnetic field and temperature just below the Curie temperature, T c , forming a hexagonal skyrmion lattice (SkL) in a plane perpendicular to the applied magnetic field.2 Figure 1 | Visualisation of the skyrmion tube spin texture. Three dimensional visualisation of three magnetic skyrmion tubes from the micromagnetic simulations presented in this paper, illustrating their extended spin structure. The inset highlights the location of the magnetic Bloch point at the end of each skyrmion tube. 3The three dimensional visualisation in Fig. 1 depicts the extended spin structure of three magnetic skyrmion tubes. The dynamics of this skyrmion tube (SkT) state play an important role in the creation and annihilation of skyrmions. For example, metastable skyrmions, which are created beyond the equilibrium thermal range by rapid field cooling 16 , are thought to unwind into topologically trivial magnetic states through the motion of a magnetic Bloch point located at the end of each individual skyrmion tube 3, 5 . Real-space observation of this dimension of the SkT state and its associated dynamics requires an in-plane magnetic field applied perpendicular to the imaging axis. Electron imaging techniques such as Fresnel Lorentz Transmission Electron Microscopy (LTEM) 12, 13 , and elec...

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We present an unreported magnetic configuration in epitaxial La(1-x) Sr(x) MnO3 (x ∼ 0.3) (LSMO) films grown on strontium titanate (STO). X-ray magnetic circular dichroism indicates that the remanent magnetic state of thick LSMO films is opposite to the direction of the applied magnetic field. Spectroscopic and scattering measurements reveal that the average Mn valence varies from mixed Mn(3+)/Mn(4+) to an enriched Mn3+ region near the STO interface, resulting in a compressive lattice along the a, b axis and a possible electronic reconstruction in the Mn e(g) orbital (d(3)z(2)-r(2). This reconstruction may provide a mechanism for coupling the Mn3+ moments antiferromagnetically along the surface normal direction, and in turn may lead to the observed reversed magnetic configuration.