Toshiro Tomida

Magnetic properties of fine crystalline Fe-P-C-Cu-X alloys

The crystallization process and magnetic properties of Fe–P–C–Cu–Ge–Si amorphous alloys were investigated. After annealing above the crystallization temperature, the bcc Fe particles, with nanoscale grain size, precipitated in the amorphous alloy for a wide P concentration range. The volume ratio of the bcc Fe phase to amorphous was about 30%. The mixed phase of these alloys shows a drastic decrease of coercive force (Hc) and particle diameter (d) as P concentration increases. The lowest Hc was obtained for Fe78P16C2Cu0.5Ge3Si0.5, and Hc and d were 1.8 A/m and 16 nm, respectively. Observation by in situ Lorentz scanning electron microscopy (SEM) revealed that the width of magnetic domains were 0.01 or 0.1 mm and the domain walls with smaller bcc Fe particles moved in a weaker magnetic field than those with larger ones. So the low Hc is attributed to the decrease of magnetocrystalline anisotropy caused by fine structures. The core loss of fine crystalline Fe–P–C–Cu–Si–Mo alloy, W14/50, was 0.22 W/kg after ...

Crystallization process of a rapidly quenched Fe-B-Nd nanocomposite magnet

Abstract Superior magnetic properties of Nd–Fe–B nanocomposite magnets rely on their nanoscaled structure composed of hard-magnetic Nd 2 Fe 14 B and soft-magnetic Fe 3 B phases, which results from a glassy state upon subsequent annealing. It has been known from X-ray diffraction (XRD) analysis that for this system, an addition of Cr is critical to control the crystallization route to produce the desired mixture of Nd 2 Fe 14 B and Fe 3 B phases. We have investigated the partitioning of Cr in a Nd 5 Fe 74.5 B 18 Cr 2.5 alloy throughout its crystallization process using atom probe field ion microscopy (APFIM). Cr is found to be enriched in Fe 3 B, up to 4.7 at.%, and the Cr concentration in Nd 2 Fe 14 B is determined to be 0.70 at.%. Together with the results of XRD, we have discussed the effect of Cr, based on the idea that Cr alters the phase decomposition route by stabilizing the Fe 3 B phase.

Origin of magnetic anisotropy formation in the HDDR-process of Nd2Fe14B-based alloys

To clarify the mechanism inducing magnetic anisotropy in the hydrogenation, disproportionation, desorption and recombination process of NdFeB-based alloys, the disproportionation of Nd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0 and its relation to the magnetic properties have been investigated. The disproportionated microstructure under optimum hydriding conditions for energy product mainly consists of the coarse-grained α-Fe and Fe.B involving two kinds of particle. One is NdH2 particles, and the other has been identified as “crystallographically aligned” Nd2Fe14B particles. The size of the Nd2Fe14B particles is less than 50 nm. The crystallographic orientation of the nano-scale Nd2Fe14B particles is almost the same as that of the original Nd2Fe14B. It is therefore most likely that this nano-scale Nd2Fe14B acts as a recombination center during the desorption leading to the magnetic anisotropy formation.

New aspects of Nd–Fe–B-based hydrogenation-disproportionation-desorption-recombination powders and anisotropic bonded magnets made from them: Microstructure and magnetic properties (invited)

Recent progress in the understanding of the texture formation mechanism in the hydrogenation-disproportionation-desorption-recombination (HDDR) process, improvements of stability with regard to thermal and structural losses, and the state-of-the-art performance of both compression and injection molded magnets made from the newly developed anisotropic HDDR powders are reported. Transmission electron microscopy observations of disproportionated Nd–Fe–Co–Ga–Zr–B alloys have revealed the existence of finely dispersed crystallites of Nd2(Fe,Co,Ga)14B which have a common crystallographic orientation. It is proposed that, upon removal of hydrogen, the hydrogen-disproportionated structure recombines from these crystallites to form textured submicron crystallites of the 2:14:1 phase. Using highly anisotropic HDDR powders, energy products (BH)max exceeding 170 kJ/m3 (21 MGOe) have been obtained on compression-molded resin-bonded magnets and 130 kJ/m3 (16 MGOe) on injection-molded ones. High coercivity HDDR powders ...

Cube-textured Si-steel sheets by oxide-separator-induced decarburization and growth mechanism of cube grains

Oxide-separator-induced decarburization causes a pronounced cube-texture development in Si-steel sheets. Cube grains nucleate prior to the decarburization, and they then selectively grow when a diffusion-induced transformation occurs. The 0.35 mm thick cube-textured strips show 2D magnetic properties with an almost ideal four-fold symmetry as well as surprisingly low core losses in the easy magnetizing directions.

Effect of Cr-doping on crystallization sequence and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets

Abstract Crystallization sequence starting from Nd x Fe 82 − x B 18 and Nd x Fe 79 − x Cr 3 B 18 (x = 3.5 – 5.5 at%) amorphous alloys has been investigated using X-ray diffractometer. In the alloys with Nd concentration around 5 at%, the intermediate compound Nd 2 Fe 23 B 3 first crystallizes along with Fe 3 B from the amorphous state. Then, the Nd 2 Fe 23 B 3 phase decomposes to form a mixture of Nd 2 Fe 14 B, Fe 3 B and αFe for the Cr-bearing systems, whereas it breaks up into another mixture of αFe and NdFe 4 B 4 for the Cr-free systems. Atom probe field ion microscopy analysis has revealed that Cr is preferentially partitioned into the Fe 3 B phase during the crystallization process, which may stabilize the Fe 3 B-containing mixture exhibited in the Cr-doped systems. We can conclude that a large fraction of Nd 2 Fe 14 B produced from the distinct decomposition scheme of the intermediate Nd 2 Fe 23 B 3 phase exhibited in the Cr-doped systems brings about the high coercivity materials.

ORIENTATIONAL MEMORY SITE IN HYDROGENATION DISPROPORTIONATION DESORPTION RECOMBINATION PROCESS OF ANISOTROPIC ND2FE14B-BASED MAGNETS

To clarify the orientational memory site in the hydrogen disproportionation desorption recombination process of Nd2Fe14B-based anisotropic magnets, high resolution transmission electron microscopy (HRTEM) characterization of hydrogen disproportionated structure of Nd13.0Fe67.9Co11.0Ga1.0Zr0.1B7.0 has been performed. In particular, crystallographic orientations of disproportionated products relative to that of parent or original Nd2Fe14B have been carefully analyzed using partially disproportionated samples. No apparent orientational coherency exists between the disproportionated products of α-Fe, Fe2B, and NdH2 and the parent Nd2Fe14B. However, nanoscale Nd2Fe14B particles of 10 to 100 nm in diameter have been detected by HRTEM to be densely present within the disproportionated mixture. Lattice fringe observation has also revealed that the crystallographic axes of the Nd2Fe14B particles are nearly parallel to those of the original Nd2Fe14B. It is thus suggested that these Nd2Fe14B particles be the orienta...

Development of a thermoelectric power generation system using reciprocating flow combustion in a porous FeSi2 element

A thermoelectric power generation system using reciprocating flow combustion in a porous thermoelectric conversion element has been developed and examined in its performance. Mn- (n-type) and Co- (p-type) doped FeSi2 powders were molded into the cylindrical element via a spark plasma sintering process, in which Mn- and Co-doped parts were separated by a thin insulator sheet exclusive of a terminus. The porous element consisted of two semicylindrical p/n couples, arranged electrically in series but thermally in parallel. A thermopower of 1.0–1.2 mV/K at 295–624 K and an apparent internal resistivity of 1.6×10−1 Ω cm at 556–624 K have been obtained for the element. A power generation system was then made using a pair of the elements, which were arranged lengthwise in a cylindrical combustion chamber. A reciprocatory flow of dilute fuel gas was introduced into the element, and it was ignited between the element. A steep temperature gradient of about 200 K/cm was formed lengthwise in both elements. The energy...

Magnetic properties and microstructure studies of NdFeB thin films

Abstract We have directly crystallized NdFeB magnetic thin films onto heated substrates by rf sputtering. The crystallographic texture, microstructure and phase composition of the films were investigated by XRD, SEM and TEM, and the magnetic properties were measured using a VSM. The main phase of the films is the Nd 2 Fe 14 B phase, whose tetragonal c -axis is aligned perpendicular to the film plane. The films also contain the B-rich Nd 1.1 Fe 4 B 4 phase, an amorphous phase and possibly the B-substituted NdO. For most of the films, the direction perpendicular to the film plane is the easy magnetization direction, along which the maximum coercive field obtained is 4.52 kOe and the remnant magnetization is more than 1 T after demagnetization field correction.

Structural studies of some hydrogen-treated materials related to the HDDR-process of Nd/sub 2/Fe/sub 14/B-based alloys

Hydrogen-treated Nd/sub 14.0/Fe/sub 66.9/Co/sub 11.0/Ga/sub 1.0/Zr/sub 0.1/B/sub 7.0/ alloys have been examined by means of powder X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to understand the mechanism of the development of magnetic anisotropy in the hydrogenation, decomposition, desorption, and recombination (HDDR) process of Nd/sub 2/Fe/sub 14/B-based alloys. It has been revealed that Nd/sub 2/Fe/sub 14/B phase can coexist in equilibrium with decomposed products, namely, /spl alpha/-Fe, NdH/sub 2/, and Fe/sub 2/B, in the presence of hydrogen of an atmospheric pressure over the temperature ranging 1113 to 1153 K. It was observed that Co and Ga condensed into a Nd/sub 2/Fe/sub 14/B phase during hydrogen-treatments, resulting in a thermodynamically stable Nd/sub 2/(Fe,Co,Ga)/sub 14/B compound. Well-developed anisotropic materials were obtained via the HDDR-process when the hydrogen-treatment was accomplished under such conditions that Nd/sub 2/(Fe,Co,Ga)/sub 14/B coexists with the decomposed products. All our results give a favorable support to the previous proposal that the crystallographic orientation of the original alloy can be conveyed via the undecomposed Nd/sub 2/Fe/sub 14/B particles through-out HDDR processing.