Exploring the magnetic microstructure of spinodal alloys with differential phase contrast scanning transmission electron microscopy (DPC-STEM)

Spinodal alloys are intriguing and promising materials for exploring the relationship between thechemical and the magnetic microstructure of magnetic alloys. The spinodal decomposition of suchalloys due to heating treatments within the miscibility gap results in a segregation of a magneticphase embedded in a non-magnetic matrix and is well known [1]. Although the compositionalevolution of the microstructure and its manipulation has been subject of studies, little is knownabout the magnetic microstructure. Differential phase contrast (DPC) carried out in scanningtransmission electron microscopy ((S)TEM) mode is an electron microscopy technique capable ofdoing so [2,3].In this study, we investigated the chemical microstructure and the magnetic domain structure ofspinodally decomposed Cu52Ni34Fe14 and Fe54Cr31Co15 alloys. We were able to shed light on thematerial microstructures by combining high-angle annular dark field imaging (HAADF),energy-dispersive X-ray spectroscopy (EDXS) elemental mapping and DPC-STEM imaging,revealing interesting relationships between compositional and magnetic properties of these alloys.For Cu52Ni34Fe14, overlaying EDXS elemental maps for Cu, Ni and Fe revealed a segregation ofNiFe-rich platelets within a Cu-rich matrix. These platelets are ferromagnetic and form a pattern ofsmall rectangular shaped 90° and 180° magnetic domains, which is displayed by the in-planemagnetic induction map acquired by DPC-STEM (Fig 1. (b)). There, the direction of the magneticvector is plotted as a function of hue, which also helped to determine <111> as the magnetic easyaxis for this alloy.Fe54Cr31Co15 segregates into ferromagnetic FeCo-rich particles embedded in a Cr-rich matrix. Theinduction map reveals a wavelike/lamellar and less regular magnetic domain structure comparedto Cu52Ni34Fe14, highlighting the deep insights into the magnetic domain structure gained byDPC-STEM.