Magnetic and structural characterization of Mo-Hitperm alloys with different Fe/Co ratio

• Published in: Journal of alloys and compounds Vol. 509; no. 5; pp. 1994 - 2000
• Main Authors: Conde, C.F., Borrego, J.M., Blázquez, J.S., Conde, A., Švec, P., Janičkovič, D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 03.02.2011; Elsevier
• Subjects: Alloys; Cobalt base alloys; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Crystallization; Domain effects, magnetization curves, and hysteresis; Exact sciences and technology; Fe and its alloys; Ferrous alloys; HITPERM alloys; Magnetic properties and materials; Magnetization curves, magnetization reversal, hysteresis, barkhausen and related effects; Materials science; Microstructure; Mo containing alloys; Molybdenum base alloys; Nanocrystalline materials; Nanocrystalline microstructure; Nanocrystals; Nanoscale materials and structures: fabrication and characterization; Physics; Slopes; Soft magnets; Studies of specific magnetic materials; Nanocrystalline microstructure; Soft magnets; HITPERM alloys; Mo containing alloys; XRD; Nanostructures; Temperature effects; Nanocrystal; Saturation magnetization; Iron base alloys; Magnetic properties; Grain size; Curie point; Crystallization; Magnetic field effects; Magnetic hardness; Isomer shift; Crystallinity; Soft magnetic materials; Heat treatments; Boron alloys; Transmission electron microscopy; Copper alloys; Kinetics; Microstructure; Molybdenum alloys; Nanostructured materials; Cobalt alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2010.10.113

▶ Nanocrystallization kinetics results based on isothermal (TMG) and non-isothermal (DSC) experiments agree describing a strongly inhibited grain growth process. ▶ The crystalline volume fraction at the end of the nanocrystallization process is practically not affected with the increase of Co in the alloy, although it is lower than in the corresponding Co free alloy. The lattice parameter and the crystal size of the α-FeCo(Mo) phase nanocrystals decreases as the Co content in the alloy increases. ▶ Mössbauer spectra were analyzed in the frame of three different contributions: pure crystalline, interface and amorphous contribution. Comparison between TEM, XRD and Mössbauer data indicates that some Mo could be present inside the nanocrystals. ▶ Changing the Fe/Co ratio allows to increase the Curie temperature of the amorphous alloys for these compositions between room temperature and ∼800 K, and therefore, allows tuning the temperature at which the maximum magnetocaloric effect takes place opening a possibility for these alloys as potential low cost magnetic refrigerants. The influence of the Co content on the microstructure and magnetic behaviour of a series of amorphous and nanocrystalline (FeCo) 79Mo 8Cu 1B 12 alloys is reported. Changes in the magnetic properties provoked by the microstructural evolution upon different thermal treatments of as-cast samples are analyzed as well. Kinetics of nanocrystallization process can be described by an isokinetic approach. As the Co content in the alloy increases, the Curie temperature of the amorphous as-cast samples increases while the crystallization onset temperature decreases. The crystalline volume fraction as well as the mean grain size of the nanocrystals at the end of the nanocrystallization process are slightly higher for the lowest Co content alloy but smaller than in similar Hitperm Mo-free alloys. The average magnetic field and the average isomer shift of the as-cast samples show a linear increase with two slopes with the Co content of the alloy. The same tendency is found for the saturation magnetization. Combined TEM, XRD, and MS data indicate the presence of Mo atoms in the nanocrystals. At the end of the nanocrystallization process the softest magnetic behaviour corresponds to the lowest Co content alloy. The second crystallization process provokes a magnetic hardening of these alloys.