Ha. Davies et al., NANOCRYSTALLINITY AND MAGNETIC PROPERTY ENHANCEMENT IN MELT-SPUN IRON-RARE EARTH-BASE HARD MAGNETIC-ALLOYS, Journal of materials engineering and performance, 2(4), 1993, pp. 579-587
Refinement of the grain size below approximately 35 nm mean diameter i
n melt-spun FeNdB-base alloys leads to enhancement of remanent polariz
ation, J(r), above the level predicted by the Stoner-Wohlfarth theory
for an aggregate of independent, randomly oriented, and uniaxial magne
tic particles. This article summarizes the results of the recent syste
matic research on this phenomenon, including the influence of alloy co
mposition and processing conditions on the crystallite size, degree of
enhancement of J(r), and maximum energy product (BH)max. It has been
shown that the effect can also occur in ternary FeNdB alloys, without
the addition of silicon or aluminum, which was originally thought nece
ssary, providing the nanocrystallites are not magnetically decoupled b
y a paramagnetic second phase. Values of (BH)max above 160 kJ . m-3 ha
ve been achieved. The relationship between grain size, J(r), intrinsic
coercivity, (J)H(C), and (BH)max are discussed in terms of magnetic e
xchange coupling, anisotropy, and other parameters. Recent extension o
f this work to the enhancement of properties in Fe-Mischmetal-Boron-ba
se alloys and to bonded magnets with a nanocrystalline structure is al
so described.