Ferromagnetism in High Entropy Cantor alloy triggered and tuned by severe plastic deformation

Taheriniya S.; Sonkusare R.; Boll T.; Divinski S.V.; Peterlechner M.; Rösner H.; Wilde G.

Abstract

The process of severe plastic deformation (SPD) introduces unique conditions to materials, leading to the emergence of novel properties. This research specifically investigates the observation of deformation-induced ferromagnetism resulting from SPD processing. High-pressure torsion (HPT) is utilized to process both single-phase and nanocomposite high entropy alloys (HEAs). Vibrating sample magnetometry (VSM) confirms that HPT processing triggers the development of ferromagnetic properties. The distribution and alignment of magnetic domains post-SPD treatment are further examined using differential phase contrast scanning transmission electron microscopy (DPC STEM). Atom probe tomography (APT) analysis suggests that this phenomenon stems from the localized enrichment of ferromagnetic elements, particularly Ni, induced by deformation. This observation underscores the ‘cocktail effect’ in HEAs, whereby interactions between different elements has led to this unique magnetic behavior. Additionally, deliberate mechanical mixing of the CoCrFeMnNi alloy with a HfNbTaTiZr HEA, comprising non-ferromagnetic constituents, introduces a large rotational strain that alters the ferromagnetic properties. This mixing facilitates a transition from a random orientation of magnetic domains, as seen in the HPT-processed single CoCrFeMnNi alloy, to a coordinated alignment within the nanocomposite HEA.