This report focuses on the phase relations and transformations in a (Fe 0.05 Co 0.95 ) 89 Zr 7 B 4 meltspun alloy with an emphasis on crystallization and its effects on thermomagnetic properties. When as-spun ribbons are annealed at relatively low temperatures (near primary crystallization), the nucleation and growth of nonequilibrium body-centered-cubic (bcc) crystallites occurs in a residual amorphous matrix, as determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD). At intermediate temperatures, bcc crystallites continue to grow with the addition of a small volume fraction of the equilibrium face-centered-cubic (fcc) phase. It is expected that after the bcc nuclei are formed, the grains coarsen as bcc phase and do not transform to the more stable fcc phase at intermediate temperatures. At temperatures where the amorphous matrix phase dissociates into Zr intermetallics, the bcc phase is transformed into fcc and the grains coarsen significantly. Thermodynamic modeling has been used to support the nucleation of the nonequilibrium bcc phase during the early stages of crystallization. Thermomagnetic results show little reduction in the saturation magnetization as a function of annealing temperature up to the primary crystallization temperature (~420°C).

The martensite and magnetic transformations in Ni-Fe-Ga ferromagnetic shape memory alloys are very sensitive to both alloy chemistry and thermal history. A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X 2 YZ) were used to investigate how the martensite and magnetic transitions change with alloy composition and isothermal aging above and below the B2/L2 1 ordering temperature. Calorimetry and magnetometry were employed to measure the martensite transformation temperatures and Curie temperatures. Compositional variations of only a few atomic percent result in martensite start temperatures and Curie temperatures that differ by about 230 and 35 K, respectively. Aging a Ni 53 Fe 19 Ga 28 alloy for 3600 seconds at various temperatures shifts the martensite start temperature and the Curie temperature by almost 70 K. Transmission electron microscopy investigations were conducted on the aged Ni 53 Fe 19 Ga 28 alloy. The considerable variations in the martensite and magnetic transformations in these alloys are discussed in terms of microstructural differences resulting from alloy chemistry and aging treatments.

Fe-based nanocrystalline soft magnetic alloys for high-temperature applications Appl. Phys. Lett. 95, 222516 (2009); 10.1063/1.3268471 Cryogenic hysteretic loss analysis for (Fe,Co,Ni)-Zr-B-Cu nanocrystalline soft magnetic alloys Structure and magnetic properties of Co-rich nanocrystalline soft magnetic alloys with low coercivity

The present study compares the hysteretic losses of a series of eight nanocrystalline soft magnetic alloys with compositions (Fe,Co,Ni)-Zr-B-Cu. The alloys were produced by a single wheel melt spinning technique followed by isothermal annealing to promote primary crystallization. As determined by x-ray diffraction experiments, these samples consist of fcc and/or bcc crystallites with average grain diameters of less than 15nm. Vibrating sample magnetometry was employed to measure hysteresis loops at 110 and 300K. The integrated hysteresis loops were larger for the (Fe0.22Ni0.78)89−xZr7B4Cux alloys and nearly unchanged for the other alloys with one exception [i.e., (Fe0.75Co0.125Ni0.125)85.5Zr8.5B5Cu1]. Additional hysteresis measurements with varying degrees of maximum flux density (between 0.03 and 1.1T) were performed at 110 and 300K for the alloy with composition (Fe0.75Co0.125Ni0.125)85.5Zr8.5B5Cu1, annealed at 823K for 1h. A 50% reduction in hysteretic losses was observed for this sample when measured at 110K (compared to room temperature).

In this study, a series of five nanocrystalline soft magnetic alloys, with compositions equally spaced between (Co0.70Fe0.20Ni0.10)88Zr7B4Cu1 and (Co0.90Fe0.08N0.02)88Zr7B4Cu1, was fabricated by melt spinning and subsequent isothermal annealing. The alloys were annealed at 823 and 1023K for 3600s, and the resulting structure and magnetic properties are reported. X-ray diffraction indicates that 1h isothermal annealing at 823K results in body-centered cubic crystallites in the Fe∕Ni poor alloys and in a mixture of body-centered cubic and face-centered cubic crystallites in most Fe∕Ni rich alloy. The (Co0.90Fe0.08N0.02)88Zr7B4Cu1 alloy annealed at 823K has a low coercivity of 8A∕m and a relatively high saturation magnetization of 131.1Am2∕kg. The magnetic properties of these alloys are discussed in terms of their nanocrystalline microstructures.