Kimiko Urushibata

The origin of coercivity enhancement in newly prepared high coercivity Dy-free Nd-Fe-B sintered magnets

Coercivity enhancement in Nd-Fe-B sintered magnets without substitution of Dy for Nd is an important research target in the field of permanent magnets. Our newly prepared Dy-free Nd-Fe-B sintered magnets with fine crystal grain sizes of approximately 1.9 μm showed high coercivities near 1.6 MA/m. The characteristic magnetization behavior of the magnets that we have not observed previously in other Nd-Fe-B sintered magnets, under applied fields of 1.4–2.4 MA/m, appears to be responsible for the appearance of the high coercivity. In this study, we examine the origin of the characteristic magnetization mechanism and conclude that it was caused by the strong interaction between the domain walls (DWs) and the grain boundaries (GBs). We introduce our novel step method and investigate the characteristic mechanism using the method. This method can assist in clarifying whether the characteristic magnetization mechanism results from the hopping of DWs from one GB to another, and/or by magnetic reversal appearing to...

A (Nd, Zr)(Fe, Co)11.5Ti0.5Nx compound as a permanent magnet material

We studied NdFe11TiNx compounds as permanent magnet materials. The (Nd0.7,Zr0.3)(Fe0.75Co0.25)11.5Ti0.5N0.52 powder that contained a limited amount of the α-(Fe, Co) phase shows fairly good magnetic properties, such as a saturation polarization (Js) of 1.68 T and an anisotropic field (Ha) of 2.88 (Law of approach to saturation) – 4.0 MA/m (Intersection of magnetization curves). Both properties are comparable to those of the Nd2Fe14B phase.

(Sm,Zr)(Fe,Co)11.0-11.5Ti1.0-0.5 compounds as new permanent magnet materials

We investigated (Sm,Zr)(Fe,Co)11.0-11.5Ti1.0-0.5 compounds as permanent magnet materials. Good magnetic properties were observed in (Sm0.8Zr0.2)(Fe0.75Co0.25)11.5Ti0.5powder containing a limited amount of the α-(Fe, Co) phase, including saturationpolarization (Js) of 1.63 T, an anisotropic field (Ha) of 5.90 MA/m at room temperature, and a Curie temperature (Tc) of about 880 K. Notably, Js and Ha remained above 1.5 T and 3.70 MA/m, respectively, even at 473 K. The high-temperature magnetic properties of (Sm0.8Zr0.2)(Fe0.75Co0.25)11.5Ti0.5 were superior to those of Nd2Fe14B.

The origin of unique initial magnetization curves in Dy-substituted (Nd1−x, Dyx)2Fe14B (x = 0−1) sintered magnets

The coercivities (Hc), saturation magnetizations (Js), and anisotropy constants K1 of (Nd1−x, Dyx)2Fe14B sintered magnets (x = 0 to 1.0) are determined using high magnetic field measurements up to about 8 MA/m. The Ha, Js, and K1 values of samples with x < 0.5 are similar to those obtained in previous studies using single crystals; the Hc values for the sintered magnets are reported here for the first time. The magnetization into the single-domain states (SDS) in Dy-substituted sintered magnets is completed in lower fields than with Dy-free magnets (for example, 0.64 MA/m in the x = 1.0 sample and 1.6 MA/m in the x = 0.25 sample). The volume fraction of magnetized SDS grains when applying fields less than the demagnetizing fields of the samples also increases with increasing Dy content, i.e., 22 vol. % for a Dy-free sample and 48 vol. % for a Nd-free sample. A characteristic magnetization behavior of large pinning-like magnetization curves appeared in samples that were initially magnetized in a direction ...

Influence of Zr substitution on the stabilization of ThMn12-type (Nd1−αZrα)(Fe0.75Co0.25)11.25Ti0.75N1.2−1.4 (α = 0–0.3) compounds

The influence of Zr substitution in ThMn12 compounds was investigated using strip casting alloys. It was found that Zr substitution stabilized (Nd1−αZrα)(Fe0.75Co0.25)11.25Ti0.75N1.2−1.4 (α = 0–0.3) compounds. Specifically, a reduction in the lattice constant along the a-axis was observed. Energy-dispersive X-ray spectroscopy mapping combined with Cs-corrected scanning transmission electron microscopy indicated that Zr atoms preferentially occupied Nd 2a sites. Both the magnetic anisotropy field and saturationpolarization were maximum at Zr substitution ratio α = 0.1. The (Nd1−αZrα)(Fe0.75Co0.25)11.25Ti0.75N1.2−1.4 (α = 0–0.3) compounds displayed higher saturationpolarization than Nd2Fe14B at high temperatures.

Magnetic properties of the surface layer and its magnetic interaction with the interior of Nd-Fe-B sintered magnets

The magnetization and demagnetization mechanisms in the mechanically polished surface layers (SL) of the c-plane and a-b plane of Nd-Fe-B sintered magnets were investigated. The magnetic interaction between the SL and the interior of the magnet was clarified by using vibrating sample magnetometer measurements of a whole sample and magneto-force microscopy observations of the domain structure of the SL layer. The polishing eliminated the Nd-rich grain boundary phases, which was only about 2 nm thick, from the SL crystal grains in the sintered magnets. The a-b plane polishing caused the independent magnetic reversal of the a-b plane SL, which was about 5.5 μm thick, as in the platy samples. The coercivities (μ0Hc) of the SL were less than 0.3 T. In contrast, the c-plane polishing did not produce independent magnetic reversal of the SL, although the coercivity of bulk samples was clearly decreased by the formation of the c-plane SL. The grains in the SL should form clusters that alter the demagnetizing facto...