Magnetism in amorphous materials

The large atomic disorder and the absence of lattice periodicity in amorphous solids will in general lead to magnetic properties that are different from those found in their crystalline counterparts. The undelying reason is that some magnetic properties are particularly structure sensitive. Disorder in amorphous materials encompasses both structural and chemical disorder, which is indeed responsible for a variety of magnetic structures in amorphous materials. Kondo-effect, superparamagnetism, spin glass behaviour, soft and hard magnetic properties, in principle these all can be accomplished in amorphous materials by choosing an apposite route of production. In general, amorphous materials show excellent soft magnetic properties due to the lack of magnetocrystalline anisotropy and microstructural defects (grain boundaries, dislocations or precipitates) on which domain walls could be pinned. However, by controlled crystallization and microstructural development combined with local anisotropy of rare-earths, a wide range of coercivity values can be achieved. Figure 1 shows one of such prototypes: Nd₆₀Fe₁₀Co₂₀Al₁₀ alloys prepared by splat quenching, melt spinning, and mold-casting show superparamagnetic, soft, and hard magnetic behaviour at room temperature, respectively. Currently, we are investigating two different systems of alloys.

1. Nd-based binary (NdFe), ternary (NdFeAl), quaternary (NdFeCoAl) alloys:hard magnetic

2. (Fe-Co)-(Al, Ga, Si)-(B,C,D) alloys:soft magnetic

Fig.1 : The Nd60Fe10Co20Al10 alloys prepared by splat quenching, melt spinning, and mold casting.