Coercivity increase of the recycled HDDR Nd-Fe-B powders doped with DyF3 and processed via Spark Plasma Sintering & the effect of thermal treatments

Research output: Contribution to journalArticle


  • Awais Ikram
  • Muhammad Farhan Mehmood
  • Zoran Samardžija
  • Saso Sturm
  • Spomenka Kobe
  • Kristina Zuzek Rozman

Colleges, School and Institutes

External organisations

  • Jozef Stefan Institute, Ljubljana, Slovenia
  • Jožef Stefan Institute


The magnetic properties of the recycled HDDR Nd-Fe-B powder doped with a low weight fraction of DyF3 nanoparticles were investigated. Spark plasma sintering (SPS) was used to consolidate the recycled Nd-Fe-B powder blends containing 1, 2 and 5 wt. % of DyF3 grounded powder. Different post SPS sintering thermal treatment conditions (600, 750 and 900 OC) for a varying amount of time were studied in view of optimizing the magnetic properties and developing characteristic core-shell microstructure in the HDDR powder. As received recycled HDDR powder has coercivity (HCi) of 830 kA/m and as optimally as SPS-ed magnets reach 1160 kA/m after the thermal treatment. With only 1 – 2 wt. % blended DyF3, the HCi peaked to 1407 kA/m with the thermal treatment at 750 OC for 1 hour. The obtained HCi values of the blend magnet is 41% higher than the starting recycled HDDR powder and 17.5% higher than the SPS-ed processed magnet annealed at 750 OC for 1 hour. Prolonging the thermal treatment time to 6 hours and temperature conditions above 900 OC was detrimental to the magnetic properties. About ~2 wt. % DyF3 dopant was suitable to develop a uniform core-shell microstructure in the HDDR Nd-Fe-B powder. The Nd-rich phase in the HDDR powder has a slightly different and fluorine rich composition i.e. Nd-O-F2 than in the one reported in sintered magnets (Nd-O-F). The composition of reaction zone-phases after the thermal treatment and Dy diffusion was DyF4, which is more abundant in 5 wt. % doped samples. Further doping above 2 wt. % DyF3 is ineffective in augmenting the coercivity of the recycled HDDR powder due to the decomposition of the shell structure and formation of non-ferromagnetic rare earth based complex intermetallic compounds. The DyF3 doping is a very effective single step route in a controlled coercivity improvement of the recycled HDDR Nd-Fe-B powder from the end of life magnetic products.


Original languageEnglish
Article number1497
Issue number9
Publication statusPublished - 8 May 2019


  • HDDR Nd2Fe14B, Recycling, Rare Earth Permanent Magnets, Spark Plasma Sintering, Coercivity, Doping DyF3