ORALS

SESSION: SISAMFriPM2-R3 F: Metastability & sustainability	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Fri Oct, 25 2019 / Room: Dr. Christian Bernard
Session Chairs: Michael J. Zehetbauer; Session Monitor: TBA

16:45: [SISAMFriPM211] Invited
Towards High Coercivities in Heavy Rare Earth Free Nd-Fe-B Ribbons
Marko Soderžnik¹ ; Matic Korent² ; Urska Ročnik³ ; Boris Saje⁴ ; Spomenka Kobe⁵ ; ¹Jožef Stefan Institute, Ljubljana, Slovenia; ²Jozzef Stefan Institute, LJUBLJANA, Slovenia; ³Department for Nanostructured Materials, Jožef Stefan Institute, Ljubljana, Slovenia; ⁴Kolektor Magnet Technology GmbH, Essen, Germany; ⁵Josef Stefan Institute, Ljubljana, Slovenia;
Paper Id: 367 [Abstract]

Reasonable magnetic performance to weight ratio makes polymer-bonded magnets indispensable in automotive applications [i]. The magnetic powders, used for bonded magnets are mainly produced by the gas atomization and melt-spinning [ii]. Several magnetic powders can be used for such purposes, namely ferrites, SmCo, Sm-Fe-N, Nd-Fe-B and/or combinations of all of them. Since the magnetic powder is blended with non-magnetic binder, the remanent magnetization is diluting as the volume percent of the binder is increasing. Therefore, they can be classified as medium-performance isotropic bonded magnets. The coercivity of the magnet, however, is not related to the magnetic powder/non-magnetic binder ratio but to the chemistry and microstructural features. Melt-spun ribbons of Nd-Fe-B material are composed of randomly oriented Nd₂Fe₁₄B grains within the size of single magnetic domain [iii]. Therefore, they have a huge potential for higher coercivity compared to sintered Nd-Fe-B magnets in which a typical grain size is measured in microns [iv]. There exist several ways to improve the coercivity of Nd-Fe-B magnets. One way is to decouple the Nd2Fe14B grains by infiltration of low eutectic Nd-based alloys which we propose within this study. Detailed microstructural analyses showed that non-ferromagnetic Nd₇₀Cu₃₀ was successfully infiltrated between the grains, which prevented the physical contact between the grains leading to weaker intergrain exchange coupling. The results of such a process show more than 20 % improvement in coercivity while the remanence is increased as expected due to the lower amount of the ferro-magnetic phase. Significant increase in coercivity compensates lower remanence, and the energy product is also increased. In comparison to the basic powder, the coercivity at 150 °C is significantly improved, which enables these magnets to be used at a higher temperature.

References:
[i] J. J. Croat, 8-Major applications for rapidly solidified NdFeB permanent magnets, Woodhead Publishing Series in Electronic and Optical Materials (2018) 325–361.\n[ii] G. Sarriegui, J. M. Martín, M. Ipatov, A. P. Zhukov, J. Gonzalez, Magnetic Properties of NdFeB Alloys Obtained by Gas Atomization Technique, IEEE Trans. Magn. 54 (2018) 2103105.\n[iii] J. D. Livingston, Magnetic domains in sintered Fe-Nd-B magnets, J. Appl. Phys. 57 (1985) 4137–4139.\n[iv] M. Soderžnik, M. Korent, K. Žagar Soderžnik, M. Katter, K. Üstüner, S. Kobe, Acta Mat. 115 (2016) 178–284.

SESSION: SISAMSatPM2-R3 H: Characterization cont.	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Sat Oct, 26 2019 / Room: Dr. Christian Bernard
Session Chairs: Petra Jenus; Session Monitor: TBA

16:45: [SISAMSatPM211]
Metal-Bonded Magnets Based on YCo5-Type Nanocrystals
Marko Soderžnik¹ ; Matic Korent² ; Kristina Zagar Soderznik³ ; Jean-marie Dubois⁴ ; Pelin Tozman⁵ ; M. Venkatesan⁶ ; Michael Coey⁷ ; Spomenka Kobe⁸ ; ¹Jožef Stefan Institute, Ljubljana, Slovenia; ²Jozzef Stefan Institute, LJUBLJANA, Slovenia; ³Jozef Stefan Institute, Ljubljana, Slovenia; ⁴JSI - K7 Dpt for Nanostructured Materials, Ljubljana, Slovenia; ⁵NIMS, Tsukuba, Japan; ⁶School of Physics and CRANN, Trinity College, Dublin, Ireland; ⁷School of Physics, Dublin, Ireland; ⁸Josef Stefan Institute, Ljubljana, Slovenia;
Paper Id: 342 [Abstract]

Metal-bonded magnets based on YCo₅-type nanocrystals [i] were produced by hot-compaction using a spark plasma-sintering device. Zn and Zn/Al metallic binders with a melting temperature of ̴ 420°C were employed to fabricate dense cylindrical magnets. Two different pressures were used for compaction. The pressure of 400 MPa provided a metal-bonded magnet with Vickers hardness (HV10) of 460 ± 20 Vickers. The temperature coefficients for remanence (α) and coercivity (β) were derived from magnetization vs. magnetic field measurements in the temperature range of 20°C – 150°C. Temperature coefficients α and β for the Zn/Al-bonded magnet pressed with 400 MPa were -0.055 %/°C and -0.201 %/°C, respectively. The field emission gun scanning electron microscope revealed a ‘core-shell’-type microstructure. The pure YCo_4.8Fe_0.2 phase was detected in the core region whereas the shell was enriched with non-ferromagnetic Zn or Zn/Al phases. The high-resolution transmission electron microscope revealed the presence of clusters with ̴ 20 nm YCo_4.8Fe_0.2 grains. In the Zn/Al-bonded magnet, fabricated at 400 MPa, the coercivity <i>µ₀H_ci</i>, remanent magnetization σ and energy product (BH)_max were 0.87 T, 39.3 Am²/kg and 23.4 kJ/m³, respectively.[ii]

References:
[i] P. Tozman, M. Venkatesan, J. M. D. Coey, Optimization of the magnetic properties of nanostructured Y-Co-Fe alloys for permanent magnets, AIP Adv. 6 (2016) 056016.\n[ii] M. Soderžnik, M. Korent, K. Žagar Soderžnik, J.-M. Dubois, P. Tozman, M. Venkatesan, J. M. D. Coey, S. Kobe, Hot-compaction of YCo4.8Fe0.2 nanocrystals for metal-bonded magnets, J. Mag. and Magn. Mat. 460 (2018) 401-408.