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.
Highlights
Hard magnetic materials have proven to be indispensable in modern technology
They can be characterized by few macroscopic parameters, including: (i) the coercivity field (J Hc )—which refers to the maximum reversed magnetic field up to which the hard magnetic specimen resist demagnetization; (ii) the polarization remanence (Jr )—the value of magnetic polarization measured at zero external magnetic field for the initially magnetically saturated specimen; (iii) maximum magnetic energy product (BH)max —the amount of magnetic energy that can be stored in the magnet and (iv) the
The high efficiency of miniature magnetic components of various devices is caused by the presence of the RE2 Fe14 B phase, that reveals high magnetic anisotropy, leading to high coercivity (J Hc ) and maximum magnetic energy product (BH)max
Summary
Hard magnetic materials have proven to be indispensable in modern technology. They can be characterized by few macroscopic parameters, including: (i) the coercivity field (J Hc )—which refers to the maximum reversed magnetic field up to which the hard magnetic specimen resist demagnetization;. The second, and definitely novel approach, is the devitrification annealing of bulk glassy precursors, that can by produced by injection-casting or suction-casting techniques [25,26] in various forms, for example rods, tubes or plates The advantages of this approach are: (i) much higher corrosion resistance, due to the formation of a fully dense structure, (ii) a lack of dilution of magnetic phase within the binding polymer (which results in the reduction of Jr and (BH)max ) and (iii) reduction of the processing time, a reduction of the final costs of the product. Our current studies are focused on the investigations of the phase constitution, microstructure and magnetic properties of the melt-spun ribbons, and suction-cast plates of this alloy, subjected to annealing at various temperatures
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