Structure and some magnetic properties of amorphous and partially crystallized Fe-(Co)-Mn-Mo-B alloys09 Dec 2019 06:28
Microstructure, revealed by X-ray diffraction and transmission Mössbuaer spectroscopy, and some thermomagnetic properties of the amorphous Fe70-xCoxMn10Mo5B15 (x = 0, 0.25 and 0.5) alloys in the as-quenched state and after accumulative annealing at , , and for 0.5h have been studied. After the annealing at and then at the ribbons remain in the amorphous state, whereas after the final heat treatments at and they are partially crystallized. The grains of the hexagonal ε-Fe80Mn20 phase, 8 nm and 12 nm in size after the annealing at and for x=0 and 0.5, respectively, are paramagnetic at room temperature the first product of crystallization. After the final annealing at in samples containing Co (x=0.25 and x=0.5) α-Fe grains are also detected. X-ray diffraction studies are qualitatively very consistent with transmission Mössbauer spectra measurements. The Curie temperature () for x=0 decreases after the annealing at in comparison with the as-quenched state and then increases after the heat treatment at , whereas in the alloys containing Co atoms (x=0.25 and 0.5) only the increase of on annealing at and at is observed as compared to the as-quenched state. Isothermal magnetic entropy change is rather modest and reaches its peak value in the vicinity of the Curie temperature of the amorphous phase. The higher the larger peak value of the magnetic entropy change. An attempt to elucidate such behavior is undertaken.
Investigations of microstructure and some thermomagnetic properties in the amorphous and partially crystallized Fe70-xCoxMn10Mo5B15 (x = 0, 0.25 and 0.5) alloys have been performed. The samples annealed accumulatively at and then at for 0.5h remain in the amorphous state, whereas the specimens heat treated further at and are partially crystallized. The crystalline grains of the hexagonal ε-Fe80Mn20 phase 8 nm and 12 nm in size after the annealing at and , respectively, are the first product of crystallization in all samples studied. Moreover, in the specimens containing Co (x=0.25 and x=0.5) the crystalline grains of the α-Fe phase appear in the samples annealed finally at . X-ray diffraction studies are qualitatively very consistent with the transmission Mössbauer spectroscopy measurements. The Curie temperature depends on the thermal history of the samples. In the case of x=0 decreases after the annealing at as compared to the as-quenched state and then increases after the annealing at due to invar effect. of the samples containing Co atoms (x=0.25 and 0.5) increases only on annealing because cobalt hinders invar effect. The magnetic entropy change is rather modest and reaches its maximum in the vicinity of . The higher is the larger is the peak value of , although this relation is not systematic.