Melt-spun alloys of Pr3(Fe0.7Co0.3)27.5Ti1.5, Pr3(Fe0.6Co0.4)27.5Ti1.5, and Pr3(Fe0.5Ga0.1Co0.4)27.5Ti1.5 prepared at linear wheel speeds of 20, 30, and 40m∕s were found to contain nanocrystalline, a mixture of nanocrystalline and amorphous, and mostly amorphous phases, respectively. Grain sizes of <10nm were observed for the crystalline phases. Annealed alloys showed an increase in grain size to 15–20nm. The Curie temperature (TC) values observed in melt-spun alloys were lower than those observed in fully crystalline alloys. A reduction of ∼55°C in TC was observed for the Pr3(Fe0.7Co0.3)27.5Ti1.5 composition compared to ∼15°C for Pr3(Fe0.6Co0.4)27.5Ti1.5. For the Ga substituted alloy with Co=0.4, a large difference of ∼50°C in TC was noted. MS values of 41 and 35emu∕g were observed in alloys with Co=0.4 and Ga=0.1, and Co=0.4, respectively, at room temperature. Ga substitution increased the anisotropy field value, HA, but lowered the intrinsic coercivity value, Hci. In the alloys with Co=0.4 and Ga=0.1, and Co=0.4, spin reorientation transitions (TSR) were observed at 220 and 140K respectively. The low values of Hci observed in melt-spun ribbons are attributed to large amounts of a soft α-Fe phase.
Superconductivity in the (YBa2Cu3)1-xNaxO7-δ System. -In the system (YBa2Cu3)1-xNaxO7-δ (x = 0.0 to 0.8) Na incorporation x ≤ 0.26 enhances the bulk superconductivity. The superconducting critical transition temp., Tc remains unchanged and the crystal keeps the orthorhombic structure of the undoped YBa2Cu3O7-. delta. with a slightly smaller unit cell. Na doping increases the sintering and grain growth kinetics which results in a higher superconducting phase volume and an improved Meissner effect even at lower processing temperature. Na-doping also enables the orthorhombic lattice to bear more oxygen at elevated temp. and increases the temp. for transition from the orthorhombic to the tetragonal phase. -(CHEN, C. H.; KUMAR, B.; J. Am. Ceram. Soc. 77 (1994) 4, 1025-1031; Grad. Mater. Eng., Univ. Dayton Res. Inst., Univ. Dayton, Dayton, OH 45469-0170, USA; EN)
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