Effective high-energy ball milling in air of Fe65Co35 alloys

Abstract

Fe65Co35 alloys are technologically relevant, especially in magnetic storage and composite permanent magnets, due to the fact that they present higher saturation magnetization per volume than any other material. Out of the various approaches undertaken for its production, mechanical ball milling remains the most common and efficient method, especially considering the large industrial scale of the applications. With the development of cost-efficient processing in mind, the influence of performing the synthesis of the FeCo alloys in air instead of the standard argon atmosphere is studied. The structural and magnetic characterization, along with the study of the oxygen content of the samples, proves that synthesizing FeCo alloys in air produce materials with nearly identical magnetic performance as their argon-milled counterpart, with the oxidation extent of the materials consisting almost exclusively of the oxide passivating layer located at the surface. In addition, no aging effect was observed in the saturation magnetization up to 6 months. It is concluded that the use of argon atmospheres, desiccators and/or glove boxes may be entirely removed from the process without affecting the magnetic properties.

FeCo Nanowire–Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products

“…As a comparison, recent reports found M s = 240–248 Am 2 /kg for Fe 65 Co 35 NWs, , although it is important to point out that NWs were fully metallic in those cases wherein the template was not removed and the NWs were not exposed to air. The M s value for 50 nm FeCo NWs is in agreement with the fact that the sample is composed of 71 wt % FeCo, which is known to have M s ≈ 210–220 Am 2 /kg. , The Co–Fe oxide shell thus has a small contribution to the overall M s . This can be explained by the fact that, on the one hand, Co ferrite with a 1:1 Fe/Co ratio has a significantly smaller M s , around 40–50 Am 2 /kg, than stoichiometric CoFe 2 O 4 , around 80 Am 2 /kg .…”

“…A small amount of Co ferrite at the shell and/or metallic Co at the core could explain the observation. Coercivity is in any case considerably higher than the normal values for FeCo isotropic particles H c ≈ 8 kA/m . It is true that, assuming a diameter-independent passivating layer thickness, as will be evidenced later in the manuscript, the oxide concentration increases as the diameter decreases, and Co ferrite is known to present a large H c .…”

Ultrafast Particle Size Reduction of Fe73.9Si15.5Cu1Nb3B6.6 by High-Energy Milling: Nb2O5 as a Marker of Permeability Enhancement and Magnetic Hardening

“…This procedure can be accomplished by ball milling processes in a controlled atmosphere. For that, most studies employ planetary milling, with low impact energy (<750 rpm) − and long execution times (tens of hours) − to reduce both particle distribution and sizes, attempting to keep the physical properties of the starting material from being devalued. However, during these processes, the permeability, the coercivity, and the saturation magnetization are highly modified mainly because of the absence of shape anisotropy of the ribbons, the occurrence of undesirable phases such as FeB and/or the excessive crystallization of the α-Fe 3 Si compound which reduces the exchange coupling due to the reduction of the amount of the amorphous matrix .…”

FeCo/ZnO composites with enhancing microwave absorbing properties: effect of hydrothermal temperature and time

“…Among all the candidates, FeCo alloys can be used as an ideal candidate because of their high saturation magnetization, high magnetic loss ability as well as high Curie temperature (T c ). 11,12 So, in this study, an FeCo/ZnO composite has been prepared by a simple one-step hydrothermal method. Furthermore, the reaction temperature and the time have an important effect on the value of the minimum reection loss and the effective frequency width.…”