Abstract
AbstractElectrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare‐earth metals is an obstacle. Creating nanocomposites of rigidly exchange‐coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic‐phase material, is a promising route toward rare‐earth‐lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange‐spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random‐anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases.
Highlights
Electrification of vehicles and renewable energy is increasing the demand for permanent magnets, but the cost and scarcity of rare-earth metals is an obstacle
Multilayers and composites made using amorphases can, in addition, create an energy product, (BH)max, con- phous alloys have the advantage that undesirable effects from, siderably larger than for a single hard phase, since the strong for example, atomic steps at interfaces and other structural coercivity Hc of the hard phase is combined with the high saturation magnetization Ms of the soft phase.[7]
The samples under investigation consist of magnetically hard Sm15Co85 (SmCo) and soft Co85(Al70Zr30)15 (CoAlZr) layers deposited by magnetron sputtering on Si substrates
Summary
The samples under investigation consist of magnetically hard Sm15Co85 (SmCo) and soft Co85(Al70Zr30) (CoAlZr) layers deposited by magnetron sputtering on Si substrates. The single layer SmCo sample, on the other hand, exhibits two positive peaks and a large negative signal in the FORC diagram (Figure 4b) This is typical for magnetic materials with a quite broad distribution of switching fields and strong internal interactions.[18,28] We note that the single-phase amorphous materials are not homogeneous below the length scale of about 10 nm[29] and that the high resolution of the FORC protocol allows us to evidence the presence of two sub-populations of regions with slightly different coercivity. It is interesting that the distribution of switching fields is narrower in the hard/soft layered samples than for the single layer SmCo sample, since it indicates that the effect of the soft phase in the amorphous nanocomposites is to reduce the amount of rare-earth material and to increase the overall saturation magnetization, and to narrow down the switching field distribution
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