Structure and magnetic properties of (Fe0.5Co0.5)88Zr7B4Cu1 nanocrystalline alloys

Abstract

The development of Fe73.5Si13.5B9Nb3Cu1 (FINEMET) by Yoshizawa et al. and Fe88Zr7B4Cu1 (NANOPERM) by Inoue et al. have shown that nanocrystalline microstructures can play an important role in the production of materials with outstanding soft magnetic properties. The FINEMET and NANOPERM materials rely on nanocrystalline α-Fe3Si and α-Fe, respectively, for their soft magnetic properties. The magnetic properties of a new class of nanocrystalline magnets are described herein. These alloys with a composition of (Fe,Co)–M–B–Cu (where M=Zr and Hf) are based on the α- and α′-FeCo phases, have been named HITPERM magnets, and offer large magnetic inductions to elevated temperatures. This report focuses on thermomagnetic properties, alternating current (ac) magnetic response, and unambiguous evidence of α′-FeCo as the nanocrystalline ferromagnetic phase, as supported by synchrotron x-ray diffraction. Synchrotron data have distinguished between the HITPERM alloy, with nanocrystallites having a B2 structure from the FINEMET alloys, with the D03 structure, and NANOPERM alloys, with the A2 structure. Thermomagnetic data shows high magnetization to persist to the α→γ phase transformation at 980 °C. The room temperature ac permeability has been found to maintain a high value of 1800 up to a frequency of ∼2 kHz. The room temperature core loss has also been shown to be competitive with that of commercial high temperature alloys with a value of 1 W/g at BS=10 kG and f=1 kHz.

Partial substitution of Co and Ge for Fe and B in Fe–Zr–B–Cu alloys: microstructure and soft magnetic applicability at high temperature

“…This value is ~40-50 A/m for the Co20Ge5 alloy and ~10 A/m for the other alloys, values much lower than those obtained for alloys with a high Co concentration [6,9]. The higher values observed for the Co20Ge5 alloy cannot be explained in terms of the microstructure (similar values of X and <D> with respect to the other alloys, see fig.…”

“…Therefore, it is evidenced that a substitution of Co for Fe decreases the thermal stability of the initial amorphous alloy, as it was found for other nanocrystalline systems [6,7,13]. On the other hand, substitution of Ge for B also decreases the stability of the amorphous alloy, although the partial substitution of Ge for Fe was reported as not affecting the crystallization onset temperature [10].…”

“…From this point of view, although the partial substitution of Co for Fe is a good candidate to enhance the high temperature applications of nanocrystalline alloys, as it was shown for other nanocrystalline compositions [6,7,13], the partial substitution of Ge for B seems to be ineffective. However, as it was demonstrated elsewhere [36], the nanocrystalline state formed in Co5Ge5 alloy shows an enhancement of about 10 % of the saturation magnetization with respect to the Co5Ge0 alloy.…”

“…Although a high saturation magnetization was achieved in HITPERM alloys [6], as well as a wide temperature range of constant permeability [8], the coercivity at room temperature increases one or two orders of magnitude with respect to the Co-free alloys (from 1-10 A/m up to ~100 A/m [6,9]). Focusing on this problem, Suzuki et al recently proposed a small substitution of Ge for Fe as a more effective way to improve soft magnetic properties at high temperatures than the partial substitution of Co for Fe [10].…”

“…The maximum Co concentration studied in the alloys is 20 at. %, in order to search for a new showed that this parameter is seriously deteriorated for higher Co contents [6][7][8][9]. Although Ge is soluble in -Fe, the benefits of its addition to NANOPERM alloys would be due to its partition to the residual amorphous matrix [10], not producing a deleterious effect on the crystalline phase.…”