Effect of Zr doping on the magnetic properties and FORC diagrams of (Nd0.8Ce0.2)1.6Fe12Co2B alloys

The microstructure and room temperature magnetic properties for (Nd0.8Ce0.2)1.6Fe12Co2BZrx (x = 0-5) nanocomposite alloys prepared by melt-spinning method and subsequent thermal annealing have been investigated. Zr addition has proved to result in relevant improvements in the microstructure and magnetic properties. The enhanced coercivity Hcj of 6.02 kOe and maximum energy products (BH)max of 15.2 MGOe have been obtained at the optimum temperature Ta with the Zr content at x = 2 and x = 3, respectively. The results of X-ray diffraction (XRD) and transmission electron microscope (TEM) indicate that a small amount of Zr addition can refine the grain size and cause a uniform distribution of soft magnetic α-Fe phase. A first-order-reversal curve (FORC) analysis is performed for the Zr-free (x = 0) sample and the Zr-doped (x = 3) sample. The FORC diagrams suggest the Zr-doped sample with a higher maximum ρ of the major peak and the flat surface is responsible for the better magnetic performance. The results of Kronmüller plot show that nucleation model is the dominating mechanism for the magnetization reversal in the Zr-free and Zr-doped alloys and give the evidence for the increase in microstructural parameter αex resulting in a drastic increase of coercivity in the Zr-doped alloy.