The phase transformation and magnetic properties of (Nd0.95La0.05)9.5FebalCo5Nb2B10.5 nanocomposite have been investigated systematically via thermomagnetic analysis, vibration sample magnetometer, x-ray diffraction, and conventional transmission electron microscopy. The Henkel plot was employed to quantify the strength of the exchange coupling between the hard and soft magnetic phases in the as-spun and the thermally treated samples. It was found that remanence Br, coercivity Hci, and maximum energy product BHmax obtained were affected by the magnetic phases present as well as the grain size of constituent phases and their distribution. The Henkel plot successfully interpreted the effect of the exchange coupling on Br, Hci, and BHmax obtained for samples treated below 750 °C. However, it became inadequate for samples treated above 750 °C. Although similar shapes of ΔM–H curves were obtained in the Henkel plot, severe degradation in Br, Hci, and BHmax was found when the thermal treatment temperature was increased from 750 to 850 °C. This degradation may be attributed to the grain growth of the main phases, from 45 to 68 nm, and the development of precipitates. In conjunction with the mass balance, the precipitated phases (presumably borides) may explain the increase in the Tc of Nd2(FeCo)14B and the decreased amount of α-Fe and Fe3B with increasing thermal processing temperature.

In this article, we report types of magnetic domain patterns caused by either dipolar coupling or exchange coupling inside a heat-treated boron-rich NdFeB melt-spun ribbon. The average grain size of the sample was about 38 nm. Single particle domains were commonly observed in Fresnel images all through the specimen, suggesting little exchange coupling among the grains in these regions. Snake-shaped long interactive domains consisting of chains of grains were found in many Foucault images at the regions where exchange coupling is weak. These domains are caused by dipolar coupling along the chains. Wider domains consisting of many grains were also observed by Fresnel images, although they were much less common than the single particle domains. The grains inside a wider domain are believed to be exchange coupled with each other. The magnetic properties of such boron-rich NdFeB composites are influenced more by the dipolar coupling than by exchange coupling between the nanocrystalline grains.

The phase transformation and the exchange coupling in (Ndo095Lao005)9.5FebaICOsNb 2BI05 have been investigated. Nanocomposites were obtained by treating amorphous precursors at temperatures ranging from 650TC to 9500C for 10 minutes. The magnetic properties were characterized via the vibrating sample magnetometer (VSM). X-ray diffraction (XRD), thermomagnetic analysis (TMA), and transmission electron microscopy (TEM) were used to perform phase identification, measure grain size, and analyze phase distribution. The strength of the exchange coupling between the magnetically hard and soft phases in the corresponding nanocomposite was analyzed via the AM-versus-H plot. It was found that the remanence (Br), coercivity (Hci), and maximum energy product (BHmax) obtained were affected by the magnetic phases present as well as the grain size of constituent phases and their distribution. The optimal magnetic performance, BHm, occurred between 700°C to 750°C, where the crystallization has completed without excessive grain growth. TMA and TEM indicated that the system was composed of three phases at this point, Nd2(Fe Co) 14B, ca-Fe, and Fe3B. The exchange coupling interaction among these phases was consistently described via the AM-versus-H plot up to 750°C. The Br, Hci, and BHmax degraded severely when the thermal treatment temperature increased from 750°C. This degradation may be attributed to the grain growth of the main phases, from 45 to 68nm, and the development of precipitates, which grew from 5nm at 750°C to 12nm at 850°C. Moreover, the amount of the precipitates was found to increase with the thermal treatment temperatures. The precipitates, presumably borides, may cause a decrease in the amount of the a-Fe and Fe 3B and result in a redistribution of the Co in the nanocomposites. The increase of the Co content in the Nd 2(Fe Co) 14B may explain the increase of its Curie temperature with the thermal treatment temperatures. In this paper, we examine the impacts of these factors on the magnetic properties of (Ndo 95Lao 05)9 5FebaICosNb2B10.5 nanocomposite.