M. Dearg | Searcharxiv

arXiv2026

Helical Magnetic Nature of $β$-Mn Structured CoZn Thin-Films Determined by a Bayesian Approach to Modeling Polarized Neutron Reflectivity Data

Chiral magnetic materials can host skyrmions and hence are of interest for numerous spintronic applications including low-power storage. To reach this goal, room temperature operation and a thin film form are needed. We have studied the chiral magnetism in a $β$-Mn structured CoZn sputtered film, with a Curie temperature of $\approx 130$ °C, by means of polarized neutron reflectometry (PNR) in order to reveal its magnetic field-temperature phase diagram. In bulk this material has a helimagnetic ground state. Here we use PNR data to show that the helimagnetism survives in a CoZn film only 100 nm thick, roughly half a helical period. Given the subtlety of differentiating the helical state from a uniform state with reduced interfacial magnetism, we have developed and employed a Bayesian approach that uses model selection to analyze our PNR data and to map out the field-temperature phase diagram of our thin film.

cond-mat.mes-hall↗

arXiv2023

Growth and Characterization of $β$-Mn Structured CoZn Thin Films

Thin films of polycrystalline $β$-Mn structure CoZn have been grown on thermally oxidized Si substrates by co-sputtering from elemental targets followed by annealing. A range of films grown with variable Co deposition power and fixed Zn deposition power were produced, so as to vary the proportions of the two elements reaching the substrate, which were annealed post-growth. Whilst all films exhibited a (211) $β$-Mn structure CoZn texture in X-ray diffraction, transmission electron microscopy showed that the composition with the highest integrated intensity for that Bragg peak contained large vacancies and was covered by a thick ZnO cap owing to being Co-deficient overall. CoZn films deposited at ratios tuned to give the optimal volume fraction of $β$-Mn were continuous, with crystallites up to 200~nm in size, with a much thinner ZnO cap layer. Magnetic measurements show that such optimal CoZn films have a Curie temperature $T_\mathrm{C} \sim 420$~K and saturation magnetization of 120~emu/cm$^3$, properties close to those reported for bulk crystals. The $β$-Mn structure is chiral (P4$_{1}$32/P4$_{3}$32 space group) and is known to give rise to a Dzyaloshinkii-Moriya interaction (DMI) that stabilizes room-temperature skyrmions in the bulk. Our thin films are thus a potential materials platform, compatible with planar processing technology, for magnetic skyrmions arising from a bulk DMI.

cond-mat.mtrl-sci↗