Structural, morphological, and magnetic properties of carbon-modified nanocrystalline Pr5Co19 alloys

Abstract

Nanocrystalline rare-earth (R) and transition metal (T) alloys are known for their outstanding magnetic properties, which are driven by the combination of (R) and (T) magnetic moments. Adding carbon (C) has been proven to alter these magnetic properties. In the present work, we use X-ray diffraction, transmission electron microscopy, and atom probe tomography to investigate and characterize the impact of carbon addition on the crystalline structure, morphology, and chemical distribution of Pr₅Co₁₉ and its carbides Pr₅Co₁₉C_x. The nanocrystalline Pr₅Co₁₉ compound was synthesized by high-energy ball milling and the addition of carbon was performed by a solid-solid reaction between Pr₅Co₁₉ and C₁₀H₁₄. TEM study revealed that after carbonation the microstructure is refined, and the mean grain size decreases from 126 nm in Pr₅Co₁₉ to 65 nm with a carbon of content 1.5. Three-dimensional APT was performed to characterize the chemical composition of Pr-Co binary systems. The analyzed Pr₅Co₁₉C_1.5 sample reveals an irregular nano-lamella structure decorated by carbon atoms, the distance between the lamellas varying from 8 to 20 nm. An under-stoichiometry of Co was found in the C-rich lamellas. Fundamental magnetic properties such as saturation magnetization M_s, exchange field H_ex and magnetic susceptibility $\chi$ of the Pr₅Co₁₉ and its carbides were calculated using the random magnetic anisotropy (RMA) method.