Structural and Magnetic Studies of Bulk Nanocomposite Magnets Derived from Rapidly Solidified Pr-(Fe,Co)-(Zr,Nb)-B Alloy

Abstract

In the present study, the phase constitution, microstructure and magnetic properties of the nanocrystalline magnets, derived from fully amorphous or partially crystalline samples by annealing, were analyzed and compared. The melt-spun ribbons (with a thickness of ~30 µm) and suction-cast 0.5 mm and 1 mm thick plates of the Pr9Fe50Co13Zr1Nb4B23 alloy were soft magnetic in the as-cast state. In order to modify their magnetic properties, the annealing process was carried out at various temperatures from 923K to 1033K for 5 min. The Rietveld refinement of X-ray diffraction patterns combined with the partial or no known crystal structures (PONKCS) method allowed one to quantify the component phases and calculate their crystalline grain sizes. It was shown that the volume fraction of constituent phases and their crystallite sizes for the samples annealed at a particular temperature, dependent on the rapid solidification conditions, and thus a presence or absence of the crystallization nuclei in the as-cast state. Additionally, a thermomagnetic analysis was used as a complementary method to confirm the phase constitution. The hysteresis loops have shown that most of the samples exhibit a remanence enhancement typical for the soft/hard magnetic nanocomposite. Moreover, for the plates annealed at the lowest temperatures, the highest coercivities up to ~1150 kA/m were measured.

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…The Rietveld refinement was performed based on the model that assumed a presence of hard magnetic Pr 2 (Fe, Co) 14 B, paramagnetic Pr 1 + x Fe 4 B 4 , and in some cases soft magnetic α-Fe crystalline phases. The detailed procedure used in the quantitative analysis was presented in [6,12]. Especially, the Rietveld-PONKCS studies allowed us to determine the phase constitution including the weight fractions of the amorphous and crystalline phases as well as to estimate the crystal sizes of the investigated rods.…”

“…We have shown in our previous studies on rapidly solidified plates of various thicknesses produced for Pr 9 Fe 50 + x Co 13 Zr 1 Nb 4 B 23 - x (x = 0, 2, 5, 8) alloys that boron content greatly influences the GFA. In the case of the Pr 9 Fe 50 Co 13 Zr 1 Nb 4 B 23 alloy, the 0.5-mm thick plates were fully amorphous while 1-mm plates were slightly crystalline and only one very low-intensity diffraction peak was detected [6,13]. However, for alloys of lower B content, the suction cast plates were all crystalline in as-cast state.…”

“…To obtain nanocrystalline samples doping of the base alloy with Zr, Ti, C, and Nb [2][3][4][5] was used. However, a more efficient approach to the tailoring of the microstructure and magnetic properties involves suitable annealing of the glassy precursor [6]. Two main factors determine the possibility of obtaining bulk glassy samples.…”

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GFA of the alloy [5][6][7]. Furthermore, doping with Zr and Nb causes the microstructure refinement of the RE-Fe-B magnets and, thus, can enhance the magnetic properties of the annealed specimens [8][9][10].

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Influence of W Addition on Phase Constitution, Microstructure and Magnetic Properties of the Nanocrystalline Pr9Fe65WxB26-x (Where: x = 2, 4, 6, 8) Alloy Ribbons

“…The most important advance in RE hard magnetic materials was made in 1984 when a new Nd 2 Fe 14 B ternary compound was announced by two independent groups-Sagawa et al [2] at Sumitomo Special Metals forming abilities. Subsequent annealing allowed us to tailor the magnetic properties of the bulk glassy samples [39].…”