National University of Science and Technology “MISiS”, Moscow, Russia:

V. P. Tarasov, Professor, Head of a Chair of Non-ferrous Metals and Gold
A. V. Kutepov, Leading Engineer of Industrial Technologies Engineering Center
O. V. Khokhlova, Engineer of a Chair of Non-ferrous Metals and Gold, e-mail: hohlova.oksana.v@gmail.com
A. V. Ryabova, Master's Degree Student of a Chair of Non-ferrous Metals and Gold

R – Fe – B alloys (R = rare-earth metals Nd and Pr) with main phase R₂Fe₁₄B are of a great scientific and practical importance for the manufacture of magnetic materials and production of permanent magnets. There are numerous papers on study of these alloys, and various methods of formation of a highcoercivity state in the alloy. The main disadvantage of hard magnetic materials (HMM) of system Nd – Fe – B is their low thermal stability. The temperature coefficient of inductance (TCI) of these materials is approximately at –0.1%/^oC. This paper shows that the substitution of Nd by Pr not only reduces the amount of harmful boron phases, but can lead to its complete disappearance. However, there are other phases remaining in the material that greatly affect the magnetic properties and the fabrication parameters of material. In this study, the effect of Pr₆O₁₁ and Tb₄O₇ oxides on the magnetic parameters of hard-magnetic material Pr15B7.2Fe (rest) at concentrations ranging up to 2.2% (weight) of Pr₆O₁₁ and 0.8% (weight) of Tb₄O₇ was investigated. During sintering of HMM Pr – Fe – B, containing Pr₆O₁₁, the oxide interacts with a high-praseodymium oxide phase forming a domain wall and destructing with formation of oxide Pr₂O₃. As a result, the domain wall is weakened, and the coercive force of magnetization H_C^I falls on 12% (for 2.2% Pr₆O₁₁). While doping the HMM Pr – Fe – B with an oxide Tb₄O₇ the oxide particles are located along the grain boundaries of Pr₂Fe₁₄B main magnetic phase, strengthening them. As a result, the coercive force of magnetization H_C^I increases on 18% (for 0.8% Tb₄O₇).
This work was carried out within the agreement between the National University of Science and Technology “MISiS” and JSC “Magneton” (Moscow, Russia) No. 1/2015 (28.07.2015), realized with the financial support by the governmental order of Russian Federation No. 218, 09.04.2010.

1. Wei L., Long J., Dewen W., Tianduo S., Jinghan Z. Rare-earth-transitionmetal-boron permanent magnets with smaller temperature coefficients. Journal of Less-Common Metals. 1986. Vol. 126. pp. 95–100.
2. Kablov E. N., Petrakov A. F., Piskorskiy V. P. Magnets Nd – Fe – B with high temperature stability. The 13-th International conference on constant magnets : thesis of report. Suzdal, 2000. p. 64.
3. Tarasov V. P., Ignatov A. S. Research and choice of the most efficient alloying additions for improvement of magnetic characteristics of hard magnetic materials Nd – Fe – B. Tsvetnye Metally. 2015. No. 3. pp. 24–26.
4. Melnikov S. A., Piskorskiy V. P., Belyaev I. V. et al. Temperature dependences of magnetic properties of sintered alloys Nd – Fe – B, alloyed by the alloys of rare-earth metals with transition metals. Perspektivnye materialy. 2011. No. 11. pp. 201–207.
5. Maikov V. V., Ermakov A. E. et al. The effects of mechanical grinding on the structural and magnetic properties of Dy₂Fe₁₄B_1–xC_x alloys. JMMM. 1995. Vol. 151. pp. 167–172.

6. Kablov E. N., Petrakov A. F., Piskorskiy V. P. et al. Influence of praseodymium on magnetic properties and phase composition of material Nd – Pr – Dy – Fe – Co – B. Metallovedenie i termoobrabotka metallov. 2005. No. 6. pp. 12–16.
7. Cornejo D. R., Peixoto T. R. F., Reboh S. First-order-reversal-curve analysis of Pr – Fe – B-based nanocomposites. Journal of Magnetism and Magnetic Materials. 2010. Vol. 322, No. 7. pp. 827–831.
8. Shield J. E., Liu Y., Marr R., Chen Z., Ma B. M. The effect of transition metal additions on the microstructure and properties of nanocomposite Pr – Fe – B permanent magnets. IEEE Transactions on Magnetics. 2004. Vol. 40, No. 4. pp. 2901–2903.
9. Kablov E. N., Piskorskiy V. P., Burkhanov G. S. et al. Thermal-stable ring-shaped magnets with radial texture on the basis of Nd(Pr) – Dy – Fe – Co — B. Fizika i khimiya obrabotki materialov. 2011. No. 3. pp. 43– 47.
10. Kablov E. N., Ospennikova O. G., Piskorskiy V. P. et al. Phase composition of the Pr – Dy – Fe – Co – B sintered materials. Aviatsionnye materialy i tekhnologii. 2015. No. 52 (39). pp. 5–10.
11. Valiev R. Z. Structure and mechanical properties of ultrafine-grained metals. Materials Science Engineering. 1997. Vol. 59. pp. 234–236.
12. Benabderrahmane С., Berteaud P. Nd₂Fe₁₄B and Pr₂Fe₁₄B magnets characterisation and modelling for cryogenic permanent magnet undulator applications. Nuclear Instruments and Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2012. Vol. 669. pp. 1–6.
13. Kim A. S. Effect of oxygen on magnetic properties of Nd – Fe – B magnets. Journal of Applied Physics. 2012. Vol. 64, No. 8. pp. 3571–3573.
14. Kaihong D., Hogzhu X. Nd – Fe – B magnets by low oxygen process. Proceeding of the 21st International workshop on Rare-Earth magnets and Their Applications. Bled, 2010. pp. 183–186.
15. Wil F. et al. Development of sintered NdFeB magnets are the highest. Proceedings of the 22^nd International Workshop on Rare Earth Magnets & Their Applications. Nagasaki, Japan, 2012. pp. 421–425.
16. Ding K. et al. High-energy and high-coercivity sintered NdFeB magnets are produced by oxygen-free technology. Proceedings of the 22^nd International Workshop on Rare Earth Magnets & Their Applications. Nagasaki, Japan, 2012. pp. 183–186.
17. Cui X., Cheng X. N. Effect of Dy₂O₃ intergranular addition on thermal stability and corrosion resistance of Nd – Fe – B magnets. Intermetallics. 2014. Vol. 55. pp. 118–122.
18. Skulj I., Douvalis A. P., Harris I. R. Characterisation of oxidation products of modified Nd – Fe – B type magnets. Journal of Alloys and Compounds. 2006. Vol. 407, No. 1. pp. 304–313.