Glassy state formation and magnetic properties of Co-rich ternary RE-Co-B (RE = Y, Tb, Ho) amorphous alloys

摘要

Glass forming abilities (GFA) of a ternary Y-Co-B system and its sub-binaries were calculated on the basis of semi-empirical Miedema's and geometric models. Formation enthalpies of amorphous alloys, their solid solution counterparts and the differences between both were determined and discussed. As any additional alloying element promotes formation of glassy states, ternary alloys should be favored according to the empirical rules. However, in investigated ternary system atomic radius difference between Y and B is a deciding factor. Respectively, normalized mismatch entropy and glass forming ability parameter ΔP_(HS) indicate the Y_(27)B_(73) and Y_(35)B_(65) compositions, as the best glass formers. Co-rich melt-spun RE-Co-B (RE = Y, Tb, Ho) ribbons with high GFA were prepared by rapid quenching to analyze their magnetic properties and the effect of rare earth element substitution on magnetic entropy changes. Magnetization vs. temperature curves indicate the ferromagnetic ordering in Y-containing alloy and sperimagnetic behavior for other amorphous alloys, due to the antiferrornagnetic coupling between Co and rare earth element sublattices. Linear dependence of -ΔS_m maxima on H~(2/3) is reported as a verification of second-order magnetic transition.