EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The two types of magnetic materials most important in applications are permanent magnets and soft magnetic materials, with the latter used in in transformers, electromotors, magnetic shielding, etc. This contribution will report on the discovery of an exceptionally magnetically-soft FeCoNiPdCu high-entropy alloy and investigation of the mechanism underlying its properties. Firstly, SQUID magnetometry was performed indicating interesting magnetic properties comparable to commercially used materials – a high relative permeability $μ_{r,max}\approx 3600$, a narrow and steep hysteresis curve with a coercivity of $H_{c}=115\,\mathrm{A/m}$. These properties were also accompanied by a favourably high electrical resistivity of $33.3$ μ$\mathrm{\Omega cm}$. Secondly, by HAADF STEM microscopy combined with EDS spectroscopy it was shown that during the short annealing of our FeCoNiPdCu at 1100 °C the attractive and repulsive interactions between the different atomic species cause the segregation of the elements in the alloy. The non-magnetic elements Pd and Cu form non-magnetic “spacers“ and the magnetic elements Fe, Co and Ni cluster together into magnetic domains. This particular nanocomposite structure of small magnetic domains and non-magnetic spacers of size just 2 – 5 nm is ideal as it means that the magnetic domains are magnetically single domain but still close enough to be exchange coupled. Thus, the prerequisites of the mechanism of exchange averaging of magnetic anisotropy are fulfilled in FeCoNiPdCu guaranteeing good soft-magnetic properties as long as proper heat treatment is performed.

P. Koželj, et. al. Adv. Eng. Mater 21, 1801055 (2019).