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Abstract: Resonant soft-x-ray reflectivity and vibrating sample magnetometry have been used to characterize field driven and spin orbit torque driven magnetization reversal in a CoFeTaB/Pt bilayer. Reversal of the magnetization occurs either along the applied field direction or perpendicular to the current flow direction. Magnetometry results show that field driven (current driven) coercivities are reduced by application of a current (field) highlighting the roles played by the two external parameters. In the current switching case, it is demonstrated with soft-x-ray hysteresis loops that only the layers near the interface with Pt switch, possibly highlighting the role of proximity effects of the magnetized Pt. We show how magnetization reversal perpendicular to the beam results in hysteresis behavior in the reflected intensity that is dependent on the magnetization but independent of the helicity of the circular polarization of the incident beam

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Abstract: We report a comprehensive study on the magnetic ground state of La 1.5 Ca 0.5 Co O 4 combining single crystal neutron diffraction and resonant magnetic x-ray scattering at the Co L 2 , 3 edges. Three single-crystal samples obtained from the same boule were investigated exhibiting magnetic phase transitions from a high-temperature paramagnetic phase to an antiferromagnetic phase at T N ≈ 52 K . Single crystal neutron diffraction reveals that the crystal structure at room temperature shows an orthorhombic A -centered lattice but with a and b axes almost equal in length. The structural phase transition (charge-ordering-like) from the parent tetragonal cell takes place above 523 K into the space group A 2 m m where two nonequivalent compressed and expanded Co O 6 octahedra are ordered showing a checkerboard pattern in the a b plane. The charge segregation between the nonequivalent Co sites is about 0.4(1) electrons. Resonant magnetic x-ray reflections indexed as ( 1 / 4 , 1 / 4 , 0 ) t , ( 1 / 4 , 1 / 4 , 1 ) t , and ( 1 / 4 , 1 / 4 , 1 / 2 ) t in the parent tetragonal cell were observed at low temperature at the Co L 2 , 3 -edge energy range. The resonant spectral shape, with a noticeable absence of any resonant enhancement at the Co L 2 edge, indicates that only Co 2 + -like ions participate in the magnetic ordering. The polarization analysis discloses that the orientation of Co magnetic moments is the same for the three magnetic orders and they are long-range ordered along the diagonal in the a b plane of the parent tetragonal cell with a slight tilt in the c axis. Despite the onset temperatures for the three resonant magnetic reflections being the same, ≈ 55 K , different thermal behavior is observed between ( 1 / 4 , 1 / 4 , 1 / 2 ) t and ( 1 / 4 , 1 / 4 , L ) t ( L = integer ) reflections whose intensities maximize at different temperatures, suggesting the coexistence of two magnetic arrangements. Moreover, the intensity of the ( 1 / 4 , 1 / 4 , 1 / 2 ) t magnetic reflection is at least ten times larger than that of the ( 1 / 4 , 1 / 4 , L ) t ( L = integer ) ones. On the other hand\, neutron diffraction measurements only detect a single type of antiferromagnetic ordering following the propagation vector k = ( 1 / 4 , 1 / 4 , 1 / 2 ) t that involves half of the Co atoms in the unit cell. We conclude that the bulk magnetic order in La 1.5 Ca 0.5 Co O 4 corresponds then to this propagation vector k = ( 1 / 4 , 1 / 4 , 1 / 2 ) t while ( 1 / 4 , 1 / 4 , 0 ) t and ( 1 / 4 , 1 / 4 , 1 ) t magnetic reflections correspond to a minority magnetic phase that must be due to changes in the oxygen stoichiometry near the surface.

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Abstract: Magnetic skyrmions are topologically nontrivial particles with a potential application as information elements in future spintronic device architectures. 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 host material. The study of this skyrmion tube state (SkT) is vital for furthering the understanding of skyrmion formation and dynamics for future applications. However, direct experimental imaging of skyrmion tubes has yet to be reported. Here, we demonstrate the 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 investigation into this unexplored dimension of the skyrmion spin texture.

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Abstract: By employing resonant x-ray microdiffraction, we image the magnetization and magnetic polarity domains of the Y -type hexaferrite Ba 0.5 Sr 1.5 Mg 2 Fe 12 O 22 . We show that the magnetic polarity domain structure can be controlled by both magnetic and electric fields and that full inversion of these domains can be achieved simply by reversal of an applied magnetic field in the absence of an electric field bias. Furthermore, we demonstrate that the diffraction intensity measured in different x-ray polarization channels cannot be reproduced by the accepted model for the polar magnetic structure, known as the 2-fan transverse conical (TC) model. We propose a modification to this model, which achieves good quantitative agreement with all of our data. We show that the deviations from the TC model are large and may be the result of an internal magnetic chirality, most likely inherited from the parent helical (nonpolar) phase.

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Abstract: The effect of ion etching on exchange bias in IrMn3/Co70Fe30 bilayers is investigated. In spite of the reduction of saturation magnetization caused by the embedding of Ir from the capping layer into the Co70Fe30 layer during the etching process, the exchange bias in samples with the same thickness of the Co70Fe30 layer is reducing in proportion to the etching power. X-ray magnetic circular dichroism measurements revealed the emergence of an uncompensated Mn magnetization after etching, which is antiferromagnetically coupled to the ferromagnetic layer. This suggests etching induced formation of small interfacial FeMn regions which leads to the decrease of effective exchange coupling between ferromagnetic and antiferromagnetic layers.