Small Angle Neutron Scattering Studies of Magnetic Textures: Competing Anisotropies in Vortex Lattices and Development of the Sample and Scanning-Aperture Stage for Spatially Resolved Skyrmion Lattices

The two magnetic textures of superconducting vortex lattices (VLs) and magnetic skyrmion lattices (SkLs) are very different in their formation mechanisms and host materials, yet they have many similar attributes that allow them to both be studied using the same experimental technique, small angle neutron scattering (SANS). SANS provides statistical information of an entire VL or SkL in bulk crystals and conveys information pertaining to the magnetic texture’s uniformity, orientation, separation, and phase. The VL is highly sensitive to the host superconductor’s characteristics, like anisotropies present in the system. The effects of the anisotropies in relationship with adjustable external parameters can be seen in VL orientations and domain formations. Magnetic field-angle rotations combined with adjusting the applied magnetic field magnitude creates a delicate balance between the anisotropies in MgB2. As a result, there are three distinct field-angle regimes in which the anisotropies are cooperative, balanced, and competitive, where there are unusual existences of single-domain L phases and discontinuous phase transitions into novel coexistences of the L and I phases. The previously unexplored skyrmion mesoscale encompasses how and where domains form and their relationships with other coexisting magnetic textures. The Sample and Scanning-Aperture Stage (SSAS), a bespoke apparatus designed and built by the author of this work, was specifically designed to bridge the gap between the skyrmion micro- and macroscales and perform spatially resolved measurements of SkLs. The SSAS was recently utilized to observe spatial variations in the helical phase and equilibrium and metastable SkLs in a polycrystalline sample of Co8Zn8Mn4. The spatial variations observed across a small region of the sample are remarkably consistent for the metastable skyrmions upon cooling and warming. These measurements show that the reversible transition between triangular and square SkLs upon cooling and warming are spatially reversible, reoccurring in the same sample locations.<p></p>