A. Makino

Nanocrystalline soft magnetic Fe-M-B (M = Zr, Hf, Nb) alloys and their applications

Abstract This paper reviews our results on the development of a new type of soft magnetic material with high saturation magnetic flux density (Bs) above 1.5 T as well as excellent soft magnetic properties. A mostly single bcc structure composed of α-Fe grains with about 10–20 nm in size surrounded by a small amount of an intergranular amorphous layer was obtained by crystallization of amorphous alloys prepared by melt-spinning technique. The typical nanocrystalline bcc Fe 90 Zr 7 B 3 , Fe 89 Hf 7 B 4 and Fe 84 Nb 7 B 9 ternary alloys subjected to the optimum annealing exhibit high Bs above 1.5 T as well as high effective permeability (μe) at 1 kHz above 20000. Excellent soft magnetic properties of the nanocrystalline Fe-M-B based alloys can be obtained by the decrease in the bcc grain size, magnetostriction (λ) and the increase in Tc of the intergranular amorphous phase by optimizing the crystallization process, chemical composition and adding small amounts of elements. For example, the improved FeZrNbBCu alloy shows the high ue of 160000 combined with the high Bs of 1,57 T. This excellent μe is comparable to those of nanocrystalline Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 and the zero-magnetostrictive Co based amorphous alloys, and the high Bs is comparable to those of the Fe based amorphous alloys with rather good soft magnetic properties. The excellent characteristics of a power transformer, a common mode choke coil, a pulse-transformer and a flux gate magnetic detector made of ‘NANOPERM ™ ’ were found in agreement with its very low core losses, sufficient thermal stability and low stress-sensibility of magnetic properties. The nanocrystalline Fe-M-B based alloys ‘NANOPERM ™ ’ is therefore expected to be used for many kinds of magnetic parts and devices.

Wide supercooled liquid region and soft magnetic properties of Fe56Co7Ni7Zr0–10Nb (or Ta)0–10B20 amorphous alloys

An amorphous phase with a wide supercooled liquid region before crystallization was formed in Fe56Co7Ni7Zr10−xMxB20 (M=Nb or Ta, x=0–10 at. %) alloys by melt spinning. The glass transition temperature (Tg) and crystallization temperature (Tx) increase by the dissolution of 2% M and the degree of the increase is larger for Tx, leading to maximum ΔTx(=Tx−Tg) of 85 K at 2% Nb and 87 K at 2% Ta which are larger by about 20 K than the largest value for newly developed Fe–(Al, Ga)–(P,C,B,Si) amorphous alloys. The crystallization of the Nb-containing alloys occurs through two stages of amorphous (Am)→Am′+α-Fe+γ-Fe+Fe76Nb6B18 →α-Fe+γ-Fe+Fe76Nb6B18+Fe2Zr in the range less than about 6% Nb and Am→Am′+γ-Fe→γ-Fe+Co3Nb2B5+Ni8Nb in the range above 8% Nb. The change in the crystallization process with Nb content seems to reflect the easy precipitation of γ-Fe by the increase in the number of Fe–Nb pairs with weaker bonding nature as compared with the Fe–Zr pairs. The best soft magnetic properties were obtained at 2% Nb ...

Hard magnetic properties of Fe-Nd-B alloys containing intergranular amorphous phase

Fe-rich Fe-Nd-B amorphous alloys containing 88 to 90 at% Fe annealed for 60-300 s at 923-1023 K have the nanostructure consisting of bcc-Fe, Fe/sub 14/Nd/sub 2/B and remaining amorphous phases, and exhibit rather good hard magnetic properties, i.e., remanence (Br) of 1.28 T, coercive field (iHc) of 252 kA/m and maximum energy product ((BH)/sub max/) of 146 kJ/m/sup 3/ for Fe/sub 89/Nd/sub 7/B/sub 4/. The nanoscale Fe/sub 14/Nd/sub 2/B particles with a size of about 30 nm are surrounded by the bcc-Fe and amorphous phases which act as a magnetic exchange-coupled medium. The nanoscale coexistence of the three ferromagnetic phases is important for the achievement of the rather good hard magnetic properties. The simultaneous achievement of the high Br and (BH)/sub max/ values and the residual existence of the amorphous phase for the Fe-rich alloys containing about 90 at% Fe has significant engineering importance because of the expectations of high deformability and low cost.

Effect of Ti, V, Cr, and Mn additions on the magnetic properties of a nanocrystalline soft magnetic Fe-Zr-B alloy with high magnetic flux density

The effect of the addition of Ti, V, Cr, and Mn on the magnetic properties of a nanocrystalline soft magnetic Fe–Zr–B alloy has been investigated. The addition of the elements increases both the crystallization temperature and the grain size of α-Fe. After crystallization, these elements are observed in both the α-Fe grains and the residual amorphous matrix. It has been found that V is a useful element to control magnetostriction by keeping the saturation magnetic flux density (Bs) high. The simultaneous addition of V and Mn increases Bs. The alloys with high Bs, above 1.75 T, show good soft magnetic properties as well; the Fe90V1Zr6B3 alloy exhibits high Bs of 1.75 T and high permeability (μe) of 31 000, and the Fe89.5V0.5Mn1Zr6B3 alloy exhibits high Bs of 1.78 T and high μe of 23 000. These high Bs values are almost the same as that of a Fe-6.5 wt % Si alloy. The alloys also exhibit low core loss. Therefore, nanocrystalline Fe–V–(Mn)–Zr–B alloys are expected to be applied to power electronic devices suc...

Structural and magnetic properties of nanocrystalline Fe-rich Fe-Nb-Nd-B sintered magnets produced by consolidating amorphous powders

Nanocrystalline bulk Fe/sub 88/Nb/sub 2/Nd/sub 5/B/sub 5/ and Fe/sub 86/Nb/sub 2/Nd/sub 7/B/sub 5/ alloys were made by consolidating amorphous powders with an electric-pulse-current sintering method and subsequent annealing. Bulk alloy made by consolidating amorphous powders has a higher density (the maximum density could reach 7.5 g/cm/sup 3/ consolidating at 873 K and 636 MPa) than that made by consolidating crystalline powders, presumably because the amorphous alloy softens around the crystallization temperature. The structure formed after annealing at 1023 K for 180 s shows a nanocrystalline composite consisting of bcc-Fe, Nd/sub 2/Fe/sub 14/B and Fe/sub 3/B or Fe/sub 2/B phases with grain sizes of 20-40 nm. The nanocrystalline bulk Fe/sub 88/Nb/sub 2/Nd/sub 5/B/sub 5/ alloy shows hard magnetic properties, remanence of 1.05 T, coercive force (H/sub cJ/) of 263 kA/m, maximum energy product ((BH)/sub max/) of 75 kJ/m/sup 3/.

Thermodynamic analysis of binary Fe85B15 to quinary Fe85Si2B8P4Cu1 alloys for primary crystallizations of α-Fe in nanocrystalline soft magnetic alloys

Fe-based Fe85B15, Fe84B15Cu1, Fe82Si2B15Cu1, Fe85Si2B12Cu1, and Fe85Si2B8P4Cu1 (NANOMET®) alloys were experimental and computational analyzed to clarify the features of NANOMET that exhibits high saturation magnetic flux density (Bs) nearly 1.9 T and low core loss than conventional nanocrystalline soft magnetic alloys. The X-ray diffraction analysis for ribbon specimens produced experimentally by melt spinning from melts revealed that the samples were almost formed into an amorphous single phase. Then, the as-quenched samples were analyzed with differential scanning calorimeter (DSC) experimentally for exothermic enthalpies of the primary and secondary crystallizations (ΔHx1 and ΔHx2) and their crystallization temperatures (Tx1 and Tx2), respectively. The ratio ΔHx1/ΔHx2 measured by DSC experimentally tended to be extremely high for the Fe85Si2B8P4Cu1 alloy, and this tendency was reproduced by the analysis with commercial software, Thermo-Calc, with database for Fe-based alloys, TCFE7 for Gibbs free energ...

Hard and soft magnetic properties of nanocrystalline Fe?Nd?Zr?B alloys containing intergranular amorphous phase (abstract)

The nanoscale crystalline and amorphous phases obtained by partial crystallization of an amorphous phase in rapidly solidified Fe90Nd7−xZrxB3 alloys were found to exhibit rather good hard magnetic properties in the composition range below 3 at. % Zr and good soft magnetic properties in the range above 4 at. % Zr. The hard magnetic alloys consist of nanoscale bcc–Fe and bct–Fe14Nd2B particles surrounded by the remaining amorphous phase, while the soft magnetic alloys are composed of bcc–Fe and remaining amorphous phases. The particle size is measured to be about 20 nm for the bcc–Fe phase and 15 nm for the Fe14Nd2B phase for a the former alloys and about 10 nm for the bcc–Fe phase for the latter alloys. The volume fraction of the remaining amorphous phase is evaluated to be about 20 to 30 at. % and the Nd and Zr contents are much higher than the nominal concentrations for the hard and soft magnetic alloys from the high‐resolution TEM images and nanobeam compositional analyses. The remanence (Br), intrinsic...

NANOMET ® and FINEMET ® : Investigation on the crystallization mechanism between different kinds of Fe-based soft magnetic nanocomposite alloys

The potential electrical applications for soft magnetic materials have spurred the research of Fe-based nano-crystalline alloys.

Miniaturized planar antenna with NANOMET powder cores for the VHF band application

In this paper, we present a meander line microstrip antenna with the NANOMET powder core (NPC) on the top of the antenna, thus essentially creating a magneto-dielectric substrate/superstrate for practical applications. X-ray diffraction (XRD) with Cu-Kα radiation was used to explore on nano-crystalline structure of the NANOMET powder core. The hysteresis loop of the NPC was measured with a vibrating sample magnetometer (VSM). The micrographs of the NANOMET powder and phenol resin can be observed in Fig . 1 . As shown in Fig . 1, a large frequency shift of the central resonant frequency of 10 MHz ~ 60 MHz and an enhanced bandwidth were obtained for the designed magnetic meander line antennas over the non-magnetic counterparts at 300 MHz, which shows great potential for applications in VHF band wireless communication systems.

Effects of metalloids in Fe-rich soft magnetic amorphous alloys on magnetization

A large amount of research efforts have been focused on the development of Fe-based amorphous alloys, a kind of soft magnetic materials that is promising in the potential application of motors, transformers and choke coils due to their excellent soft magnetic property. The extraordinarily low coercivity is caused by the disordered structure and the lack of micro-scale anisotropy. Generally, the inclusion of the minor alloying elements necessary for the formation of the amorphous structure can interfere with the Fe-Fe ferromagnetic exchange and reduce the maximum magnetization [1], which is a disadvantage for the efficiency and minimization of the produced devices. On the other hand, it is reported that some common alloying metalloids, such as B and P, can promote the Fe atoms in amorphous alloys into high spin state with larger magnetic moment [2]. The present study is to clarify and optimize the magnetic effect of the alloying elements in Fe-rich amorphous alloys. In this research work, ab initio molecular dynamics simulations were performed for Fe85Si2B8P-4Cu1, Fe76Si9B10P5 and Fe73.5Si13.5B9Nb3Cu1 amorphous alloys. Considering the electric charge transfer, electron structure as well as the cluster formation, it is clarified that minor inclusion of B and P can effectively absorb electrons from Fe atoms, making the radii of 3d orbitals of Fe decrease towards optimum ferromagnetic exchange between Fe-Fe atoms. However, with increasing B/P content, the replacement of Fe-Fe bonds by Fe-metalloids bonds makes severe magnetically inert p-d hybridization which reduces the spin polarization of 3d electrons as well as the magnetic moments [3]. Therefore, B and P have complicated magnetic effect in Fe-based amorphous alloys, which appears to promote magnetization with low concentration, but reduces it at larger concentration. Besides, it was found that Si shows no beneficial effect on increasing the magnetization of the amorphous alloys due to the hybridization between Si 3p and Fe 3d orbitals, although experimental data indicate that Si is good for amorphous formation or crystallization controllability [4].