Structure, nanostructure and unconventional magnetic state of the light rare-earths based Ce PrNdSm ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si0038.svg"> <mml:mrow> <mml:mi mathvariant="bold-italic">x</mml:mi> <mml:mo linebr

We present a study of structure, microstructure, nanostructure and magnetic state of the Ce x PrNdSm ( x = 0.01–1.5) medium-entropy alloys composed of the light rare earths only. Magnetic light rare earths are fundamentally different from the heavy ones, because the crystal-field interaction in the former is able to reduce or completely destroy the ionic magnetic moments at low temperatures. The alloys crystallize in a double hexagonal close-packed structure in the form of a single-phase nanostructured solid solution. The low-temperature magnetic state is inhomogeneous, being a mixture of paramagnetic domains appearing in the crystal regions with larger destruction of the moments and spin glass (SG)-type spin domains in the regions with less destructed moments. Such mixed state is intrinsic and specific to the light-lanthanide multi-component solid solutions. The SG-type domains are magnetically frustrated spin entities with broken ergodicity below the spin freezing temperature T f . In the low-Ce content alloys, the SG-type domains resemble canonical SGs, while in the Ce-concentrated alloys, some ferrimagnetically ordered clusters with nonzero spontaneous magnetization have formed additionally. The increased Ce content x continuously reduces the average exchange coupling, as evidenced from the shift of T f towards lower temperatures and the speed-up of spin dynamics into the direction of superparamagnets. • Ce x PrNdSm light-rare-earths-only high-entropy alloys were investigated. • The dhcp single-phase solid-solution alloys show specific nanostructure. • The mixed para–spin glass magnetic state is intrinsic to this kind of alloys. • The origin is the exceptional crystal-field interaction in the light rare earths.