Structural and magnetic properties of ultra-small scale eutectic CoFeZr alloys

• Development of ultra-small scale eutectic CoFeZr alloys.
• Hardness of 713 VHN was obtained for Co49.2Fe49.2Zr by lamellar spacing of 113 nm.
• Highest moment of 1.92 μB at 5 K was obtained for Co49.2Fe49.2Zr.
• Decay of magnetization at low temperature can be described by spin wave excitation.

Aiming to develop high mechanical strength and toughness by tuning ultrafine lamellar spacing of magnetic eutectic alloys, we report the mechanical and magnetic properties of the binary eutectic alloys Co90.5Zr9.5 and Fe90.2Zr9.8, as well as the pseudo-binary eutectic alloys Co82.4Fe8Zr9.6, Co78Fe12.4Zr9.6 and Co49.2Fe49.2Zr9.6 developed by suction-casting. The lower lamellar spacing around 100 nm of the eutectics Co49.2Fe49.2Zr9.6 yields a high hardness of 713(±20) VHN. Magnetic measurements reveal high magnetic moment of 1.92 μB (at 5 K) and 1.82 μB (at 300 K) per formula unit for this composition. The magnetization vs. applied field data at 5 K show a directional preference to some extent and therefore smaller non-collinear magnetization behavior compared to Co11Zr2 reported in the literature due to exchange frustration and transverse spin freezing owing to the presence of smaller Zr content. The decay of magnetization as a function of temperature along the easy axis of magnetization of all the eutectic compositions can be described fairly well by the spin wave excitation equation ΔM/M(0) = BT3/2 + CT5/2.